ARM Linux 3.x 的设备树（Device Tree）之DTB、DTS
2016-07-05 11:25
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1、ARM Device Tree起源
Linus Torvalds在2011年3月17日的ARM Linux邮件列表宣称“this whole ARM thing is a f*cking pain in the ass”，引发ARM Linux社区的地震，随后ARM社区进行了一系列的重大修正。在过去的ARM Linux中，arch/arm/plat-xxx和arch/arm/mach-xxx中充斥着大量的垃圾代码，相当多数的代码只是在描述板级细节，而这些板级细节对于内核来讲，不过是垃圾，如板上的platform设备、resource、i2c_board_info、spi_board_info以及各种硬件的platform_data。读者有兴趣可以统计下常见的s3c2410、s3c6410等板级目录，代码量在数万行。社区必须改变这种局面，于是PowerPC等其他体系架构下已经使用的Flattened Device Tree（FDT）进入ARM社区的视野。Device Tree是一种描述硬件的数据结构，它起源于 OpenFirmware (OF)。在Linux 2.6中，ARM架构的板极硬件细节过多地被硬编码在arch/arm/plat-xxx和arch/arm/mach-xxx，采用Device Tree后，许多硬件的细节可以直接透过它传递给Linux，而不再需要在kernel中进行大量的冗余编码。
Device Tree由一系列被命名的结点（node）和属性（property）组成，而结点本身可包含子结点。所谓属性，其实就是成对出现的name和value。在Device Tree中，可描述的信息包括（原先这些信息大多被hard code到kernel中）：
CPU的数量和类别
内存基地址和大小
总线和桥
外设连接
中断控制器和中断使用情况
GPIO控制器和GPIO使用情况
Clock控制器和Clock使用情况
它基本上就是画一棵电路板上CPU、总线、设备组成的树，Bootloader会将这棵树传递给内核，然后内核可以识别这棵树，并根据它展开出Linux内核中的platform_device、i2c_client、spi_device等设备，而这些设备用到的内存、IRQ等资源，也被传递给了内核，内核会将这些资源绑定给展开的相应的设备。
2、Device Tree组成和结构
整个Device Tree牵涉面比较广，即增加了新的用于描述设备硬件信息的文本格式，又增加了编译这一文本的工具，同时Bootloader也需要支持将编译后的Device Tree传递给Linux内核。DTS (device tree source)
.dts文件是一种ASCII 文本格式的Device Tree描述，此文本格式非常人性化，适合人类的阅读习惯。基本上，在ARM Linux在，一个.dts文件对应一个ARM的machine，一般放置在内核的arch/arm/boot/dts/目录。由于一个SoC可能对应多个machine（一个SoC可以对应多个产品和电路板），势必这些.dts文件需包含许多共同的部分，Linux内核为了简化，把SoC公用的部分或者多个machine共同的部分一般提炼为.dtsi，类似于C语言的头文件。其他的machine对应的.dts就include这个.dtsi。譬如，对于VEXPRESS而言，vexpress-v2m.dtsi就被vexpress-v2p-ca9.dts所引用，
vexpress-v2p-ca9.dts有如下一行：
/include/ “vexpress-v2m.dtsi”
当然，和C语言的头文件类似，.dtsi也可以include其他的.dtsi，譬如几乎所有的ARM SoC的.dtsi都引用了skeleton.dtsi。
.dts（或者其include的.dtsi）基本元素即为前文所述的结点和属性：
<code class="hljs applescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">/ {
node1 {
a-<span class="hljs-type" style="box-sizing: border-box;">string</span>-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"A string"</span>;
a-<span class="hljs-type" style="box-sizing: border-box;">string</span>-<span class="hljs-type" style="box-sizing: border-box;">list</span>-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"first string"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"second string"</span>;
a-byte-data-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x01</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x23</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x34</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x56</span>];
child-node1 {
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">first</span>-child-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span>;
<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">second</span>-child-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>>;
a-<span class="hljs-type" style="box-sizing: border-box;">string</span>-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Hello, world"</span>;
};
child-node2 {
};
};
node2 {
an-empty-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span>;
a-cell-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">property</span> = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>>; /* each <span class="hljs-type" style="box-sizing: border-box;">number</span> (cell) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> a uint32 */
child-node1 {
};
};
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>上述.dts文件并没有什么真实的用途，但它基本表征了一个Device Tree源文件的结构：
1个root结点”/”；
root结点下面含一系列子结点，本例中为”node1” 和 “node2”；
结点”node1”下又含有一系列子结点，本例中为”child-node1” 和 “child-node2”；
各结点都有一系列属性。这些属性可能为空，如” an-empty-property”；可能为字符串，如”a-string-property”；可能为字符串数组，如”a-string-list-property”；可能为Cells（由u32整数组成），如”second-child-property”，可能为二进制数，如”a-byte-data-property”。
下面以一个最简单的machine为例来看如何写一个.dts文件。假设此machine的配置如下：
1个双核ARM Cortex-A9 32位处理器；
ARM的local bus上的内存映射区域分布了2个串口（分别位于0x101F1000 和 0x101F2000）、GPIO控制器（位于0x101F3000）、SPI控制器（位于0x10170000）、中断控制器（位于0x10140000）和一个external bus桥；
External bus桥上又连接了SMC SMC91111 Ethernet（位于0x10100000）、I2C控制器（位于0x10160000）、64MB NOR Flash（位于0x30000000）；
External bus桥上连接的I2C控制器所对应的I2C总线上又连接了Maxim DS1338实时钟（I2C地址为0x58）。
其对应的.dts文件为：
<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">/</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,coyotes-revenge"</span>;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupt<span class="hljs-attribute" style="box-sizing: border-box;">-parent</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><&</span>intc<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
cpus {
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
cpu@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,cortex-a9"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
cpu@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,cortex-a9"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
};
serial@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span>f0000 {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl011"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f0000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
serial@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span>f2000 {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl011"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f2000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
gpio@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span>f3000 {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl061"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f3000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x101f4000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x0010</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
intc: interrupt<span class="hljs-attribute" style="box-sizing: border-box;">-controller</span>@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10140000</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl190"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10140000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupt<span class="hljs-attribute" style="box-sizing: border-box;">-controller</span>;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#interrupt</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
spi@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10115000</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl022"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10115000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
external<span class="hljs-attribute" style="box-sizing: border-box;">-bus</span> {
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
ranges <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10100000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 1, Ethernet</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10160000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 2, i2c controller</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x30000000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 3, NOR Flash</span>
ethernet@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"smc,smc91c111"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">5</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
i2c@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,a1234-i2c-bus"</span>;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#address</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">#size</span><span class="hljs-attribute" style="box-sizing: border-box;">-cells</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">6</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
rtc@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"maxim,ds1338"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
};
flash@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,k8f1315ebm"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"cfi-flash"</span>;
reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x4000000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
};
};
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li><li style="box-sizing: border-box; padding: 0px 5px;">49</li><li style="box-sizing: border-box; padding: 0px 5px;">50</li><li style="box-sizing: border-box; padding: 0px 5px;">51</li><li style="box-sizing: border-box; padding: 0px 5px;">52</li><li style="box-sizing: border-box; padding: 0px 5px;">53</li><li style="box-sizing: border-box; padding: 0px 5px;">54</li><li style="box-sizing: border-box; padding: 0px 5px;">55</li><li style="box-sizing: border-box; padding: 0px 5px;">56</li><li style="box-sizing: border-box; padding: 0px 5px;">57</li><li style="box-sizing: border-box; padding: 0px 5px;">58</li><li style="box-sizing: border-box; padding: 0px 5px;">59</li><li style="box-sizing: border-box; padding: 0px 5px;">60</li><li style="box-sizing: border-box; padding: 0px 5px;">61</li><li style="box-sizing: border-box; padding: 0px 5px;">62</li><li style="box-sizing: border-box; padding: 0px 5px;">63</li><li style="box-sizing: border-box; padding: 0px 5px;">64</li><li style="box-sizing: border-box; padding: 0px 5px;">65</li><li style="box-sizing: border-box; padding: 0px 5px;">66</li><li style="box-sizing: border-box; padding: 0px 5px;">67</li><li style="box-sizing: border-box; padding: 0px 5px;">68</li><li style="box-sizing: border-box; padding: 0px 5px;">69</li><li style="box-sizing: border-box; padding: 0px 5px;">70</li><li style="box-sizing: border-box; padding: 0px 5px;">71</li><li style="box-sizing: border-box; padding: 0px 5px;">72</li><li style="box-sizing: border-box; padding: 0px 5px;">73</li><li style="box-sizing: border-box; padding: 0px 5px;">74</li><li style="box-sizing: border-box; padding: 0px 5px;">75</li><li style="box-sizing: border-box; padding: 0px 5px;">76</li><li style="box-sizing: border-box; padding: 0px 5px;">77</li><li style="box-sizing: border-box; padding: 0px 5px;">78</li><li style="box-sizing: border-box; padding: 0px 5px;">79</li><li style="box-sizing: border-box; padding: 0px 5px;">80</li><li style="box-sizing: border-box; padding: 0px 5px;">81</li><li style="box-sizing: border-box; padding: 0px 5px;">82</li><li style="box-sizing: border-box; padding: 0px 5px;">83</li></ul>上述.dts文件中,root结点”/”的compatible 属性compatible = “acme,coyotes-revenge”;定义了系统的名称，它的组织形式为：,。Linux内核透过root结点”/”的compatible 属性即可判断它启动的是什么machine。
在.dts文件的每个设备，都有一个compatible 属性，compatible属性用户驱动和设备的绑定。compatible 属性是一个字符串的列表，列表中的第一个字符串表征了结点代表的确切设备，形式为”,”，其后的字符串表征可兼容的其他设备。可以说前面的是特指，后面的则涵盖更广的范围。如在arch/arm/boot/dts/vexpress-v2m.dtsi中的Flash结点：
<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">flash<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@0</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">00000000</span> {
compatible = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,vexpress-flash"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"cfi-flash"</span>;
reg = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x00000000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x04000000</span>>,
<<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x00000000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x04000000</span>>;
bank-width = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span>>;
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li></ul>compatible属性的第2个字符串”cfi-flash”明显比第1个字符串”arm,vexpress-flash”涵盖的范围更广。
再比如，Freescale MPC8349 SoC含一个串口设备，它实现了国家半导体（National Semiconductor）的ns16550 寄存器接口。则MPC8349串口设备的compatible属性为compatible = “fsl,mpc8349-uart”, “ns16550”。其中，fsl,mpc8349-uart指代了确切的设备， ns16550代表该设备与National Semiconductor 的16550 UART保持了寄存器兼容。
接下来root结点”/”的cpus子结点下面又包含2个cpu子结点，描述了此machine上的2个CPU，并且二者的compatible 属性为”arm,cortex-a9”。
注意cpus和cpus的2个cpu子结点的命名，它们遵循的组织形式为：[@]，<>中的内容是必选项，[]中的则为可选项。name是一个ASCII字符串，用于描述结点对应的设备类型，如3com Ethernet适配器对应的结点name宜为ethernet，而不是3com509。如果一个结点描述的设备有地址，则应该给出@unit-address。多个相同类型设备结点的name可以一样，只要unit-address不同即可，如本例中含有cpu@0、cpu@1以及serial@101f0000与serial@101f2000这样的同名结点。设备的unit-address地址也经常在其对应结点的reg属性中给出。ePAPR标准给出了结点命名的规范。
可寻址的设备使用如下信息来在Device Tree中编码地址信息：
reg
#address-cells
#size-cells
其中reg的组织形式为reg =
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> ranges = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10100000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 1, Ethernet</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10160000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x10000</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 2, i2c controller</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x30000000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000000</span>>; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// Chipselect 3, NOR Flash</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li></ul>
ranges是地址转换表，其中的每个项目是一个子地址、父地址以及在子地址空间的大小的映射。映射表中的子地址、父地址分别采用子地址空间的#address-cells和父地址空间的#address-cells大小。对于本例而言，子地址空间的#address-cells为2，父地址空间的#address-cells值为1，因此0 0 0x10100000 0x10000的前2个cell为external-bus后片选0上偏移0，第3个cell表示external-bus后片选0上偏移0的地址空间被映射到CPU的0x10100000位置，第4个cell表示映射的大小为0x10000。ranges的后面2个项目的含义可以类推。
Device Tree中还可以中断连接信息，对于中断控制器而言，它提供如下属性：
interrupt-controller – 这个属性为空，中断控制器应该加上此属性表明自己的身份；
interrupt-cells – 与#address-cells 和 #size-cells相似，它表明连接此中断控制器的设备的interrupts属性的cell大小。
在整个Device Tree中，与中断相关的属性还包括：
interrupt-parent – 设备结点透过它来指定它所依附的中断控制器的phandle，当结点没有指定interrupt-parent 时，则从父级结点继承。对于本例而言，root结点指定了interrupt-parent = <&intc>;其对应于intc: interrupt-controller@10140000，而root结点的子结点并未指定interrupt-parent，因此它们都继承了intc，即位于0x10140000的中断控制器。
interrupts – 用到了中断的设备结点透过它指定中断号、触发方法等，具体这个属性含有多少个cell，由它依附的中断控制器结点的#interrupt-cells属性决定。而具体每个cell又是什么含义，一般由驱动的实现决定，而且也会在Device Tree的binding文档中说明。譬如，对于ARM GIC中断控制器而言，#interrupt-cells为3，它3个cell的具体含义Documentation/devicetree/bindings/arm/gic.txt就有如下文字说明：
<code class="hljs applescript has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">01</span> The <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>st cell <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt type; <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> SPI interrupts, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> PPI <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">02</span> interrupts. <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">03</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">04</span> The <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span>nd cell <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">contains</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt <span class="hljs-type" style="box-sizing: border-box;">number</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt type. <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">05</span> SPI interrupts are <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> range [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">987</span>]. PPI interrupts are <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">in</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">06</span> range [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span>]. <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">07</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">08</span> The <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>rd cell <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> flags, encoded <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">as</span> follows: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">09</span> bits[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] trigger type <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">and</span> level flags. <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">10</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> = low-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span>-high edge triggered <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span> = high-<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span>-low edge triggered <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">12</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span> = active high level-sensitive <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">13</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span> = active low level-sensitive <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">14</span> bits[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span>] PPI interrupt cpu mask. Each bit corresponds <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> each <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">of</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">8</span> possible cpus attached <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> GIC. A bit <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">set</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> '<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>' indicated <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">16</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">the</span> interrupt <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">is</span> wired <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">to</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">that</span> CPU. Only valid <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">for</span> PPI interrupts.</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>
另外，值得注意的是，一个设备还可能用到多个中断号。对于ARM GIC而言，若某设备使用了SPI的168、169号2个中断，而言都是高电平触发，则该设备结点的interrupts属性可定义为：interrupts = <0 168 4>, <0 169 4>;
除了中断以外，在ARM Linux中clock、GPIO、pinmux都可以透过.dts中的结点和属性进行描述。
3、DTC (device tree compiler)
将.dts编译为.dtb的工具。DTC的源代码位于内核的scripts/dtc目录，在Linux内核使能了Device Tree的情况下，编译内核的时候主机工具dtc会被编译出来，对应scripts/dtc/Makefile中的“hostprogs-y := dtc”这一hostprogs编译target。在Linux内核的arch/arm/boot/dts/Makefile中，描述了当某种SoC被选中后，哪些.dtb文件会被编译出来，如与VEXPRESS对应的.dtb包括：
<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;">dtb<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-</span>$(CONFIG_ARCH_VEXPRESS) <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">+=</span> vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca5s</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">\</span> vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca9</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">\</span> vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca15</span><span class="hljs-attribute" style="box-sizing: border-box;">-tc1</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">\</span> vexpress<span class="hljs-attribute" style="box-sizing: border-box;">-v2p</span><span class="hljs-attribute" style="box-sizing: border-box;">-ca15_a7</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">\</span> xenvm<span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">-</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4.2</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">.</span>dtb</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>
在Linux下，我们可以单独编译Device Tree文件。当我们在Linux内核下运行make dtbs时，若我们之前选择了ARCH_VEXPRESS，上述.dtb都会由对应的.dts编译出来。因为arch/arm/Makefile中含有一个dtbs编译target项目。
4、Device Tree Blob (.dtb)
.dtb是.dts被DTC编译后的二进制格式的Device Tree描述，可由Linux内核解析。通常在我们为电路板制作NAND、SD启动image时，会为.dtb文件单独留下一个很小的区域以存放之，之后bootloader在引导kernel的过程中，会先读取该.dtb到内存。Binding
对于Device Tree中的结点和属性具体是如何来描述设备的硬件细节的，一般需要文档来进行讲解，文档的后缀名一般为.txt。这些文档位于内核的Documentation/devicetree/bindings目录，其下又分为很多子目录。
5、Bootloader
Uboot mainline 从 v1.1.3开始支持Device Tree，其对ARM的支持则是和ARM内核支持Device Tree同期完成。为了使能Device Tree，需要编译Uboot的时候在config文件中加入#define CONFIG_OF_LIBFDT
在Uboot中，可以从NAND、SD或者TFTP等任意介质将.dtb读入内存，假设.dtb放入的内存地址为0x71000000，之后可在Uboot运行命令fdt addr命令设置.dtb的地址，如：
U-Boot> fdt addr 0x71000000
fdt的其他命令就变地可以使用，如fdt resize、fdt print等。
对于ARM来讲，可以透过bootz kernel_addr initrd_address dtb_address的命令来启动内核，即dtb_address作为bootz或者bootm的最后一次参数，第一个参数为内核映像的地址，第二个参数为initrd的地址，若不存在initrd，可以用 -代替。
6、Device Tree引发的BSP和驱动变更
有了Device Tree后，大量的板级信息都不再需要，譬如过去经常在arch/arm/plat-xxx和arch/arm/mach-xxx实施的如下事情：1. 注册platform_device，绑定resource，即内存、IRQ等板级信息。
透过Device Tree后，形如
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">90</span> static struct resource xxx_resources[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">91</span> [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">92</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span> = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">93</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.end</span> = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">94</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.flags</span> = IORESOURCE_MEM,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">95</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">96</span> [<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">97</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.start</span> = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">98</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.end</span> = …,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">99</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.flags</span> = IORESOURCE_IRQ,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">102</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">103</span> static struct platform_device xxx_device = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">104</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"xxx"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">105</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.id</span> = -<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">106</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dev</span> = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">107</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.platform</span>_data = &xxx_data,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">108</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">109</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.resource</span> = xxx_resources,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">110</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.num</span>_resources = ARRAY_SIZE(xxx_resources),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">111</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li></ul>之类的platform_device代码都不再需要，其中platform_device会由kernel自动展开。而这些resource实际来源于.dts中设备结点的reg、interrupts属性。典型地，大多数总线都与“simple_bus”兼容，而在SoC对应的machine的.init_machine成员函数中，调用of_platform_bus_probe(NULL, xxx_of_bus_ids, NULL);即可自动展开所有的platform_device。譬如，假设我们有个XXX SoC，则可在arch/arm/mach-xxx/的板文件中透过如下方式展开.dts中的设备结点对应的platform_device：
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">18</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> of_device_id xxx_of_bus_ids[] __initdata = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">19</span> { <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.compatible</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"simple-bus"</span>, },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">20</span> {},
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">21</span> };
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">23</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> __init xxx_mach_init(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">24</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">25</span> of_platform_bus_probe(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>, xxx_of_bus_ids, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">26</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">32</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">33</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#ifdef CONFIG_ARCH_XXX</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">38</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">39</span> DT_MACHINE_START(XXX_DT, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Generic XXX (Flattened Device Tree)"</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">41</span> …
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">45</span> <span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.init_machine</span> = xxx_mach_init,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">46</span> …
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">49</span> MACHINE_END
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">50</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#endif</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>注册i2c_board_info，指定IRQ等板级信息。
形如
<code class="hljs cs has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">145</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> i2c_board_info __initdata afeb9260_i2c_devices[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">146</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">147</span> I2C_BOARD_INFO(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"tlv320aic23"</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1a</span>),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">148</span> }, {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">149</span> I2C_BOARD_INFO(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"fm3130"</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x68</span>),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">150</span> }, {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">151</span> I2C_BOARD_INFO(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"24c64"</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x50</span>),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">152</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">153</span> };</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>之类的i2c_board_info代码，目前不再需要出现，现在只需要把tlv320aic23、fm3130、24c64这些设备结点填充作为相应的I2C controller结点的子结点即可，类似于前面的
<code class="hljs ruby has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"> i2c<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@1</span>,<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> {
compatible = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,a1234-i2c-bus"</span>;
…
rtc<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">@58</span> {
compatible = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"maxim,ds1338"</span>;
reg = <<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">58</span>>;
interrupts = < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">7</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">3</span> >;
};
};</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>Device Tree中的I2C client会透过I2C host驱动的probe()函数中调用of_i2c_register_devices(&i2c_dev->adapter);被自动展开。
3. 注册spi_board_info，指定IRQ等板级信息。
形如
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">79</span> static struct spi_board_info afeb9260_spi_devices[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span> { <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* DataFlash chip */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">81</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.modalias</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"mtd_dataflash"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">82</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.chip</span>_select = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">83</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.max</span>_speed_hz = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">15</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span> * <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1000</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">84</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.bus</span>_num = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">85</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">86</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>之类的spi_board_info代码，目前不再需要出现，与I2C类似，现在只需要把mtd_dataflash之类的结点，作为SPI控制器的子结点即可，SPI host驱动的probe函数透过spi_register_master()注册master的时候，会自动展开依附于它的slave。
4. 多个针对不同电路板的machine，以及相关的callback。
过去，ARM Linux针对不同的电路板会建立由MACHINE_START和MACHINE_END包围起来的针对这个machine的一系列callback，譬如：
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">373</span> MACHINE_START(VEXPRESS, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ARM-Versatile Express"</span>) <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">374</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.atag</span>_offset = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x100</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">375</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.smp</span> = smp_ops(vexpress_smp_ops), <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">376</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>_io = v2m_map_io, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">377</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_early = v2m_init_early, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">378</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_irq = v2m_init_irq, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">379</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.timer</span> = &v2m_timer, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">380</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.handle</span>_irq = gic_handle_irq, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">381</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_machine = v2m_init, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">382</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.restart</span> = vexpress_restart, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">383</span> MACHINE_END</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>
这些不同的machine会有不同的MACHINE ID，Uboot在启动Linux内核时会将MACHINE ID存放在r1寄存器，Linux启动时会匹配Bootloader传递的MACHINE ID和MACHINE_START声明的MACHINE ID，然后执行相应machine的一系列初始化函数。
引入Device Tree之后，MACHINE_START变更为DT_MACHINE_START，其中含有一个.dt_compat成员，用于表明相关的machine与.dts中root结点的compatible属性兼容关系。如果Bootloader传递给内核的Device Tree中root结点的compatible属性出现在某machine的.dt_compat表中，相关的machine就与对应的Device Tree匹配，从而引发这一machine的一系列初始化函数被执行。
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">489</span> static const char * const v2m_dt_match[] __initconst = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">490</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,vexpress"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">491</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"xen,xenvm"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">492</span> NULL,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">493</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">495</span> DT_MACHINE_START(VEXPRESS_DT, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"ARM-Versatile Express"</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">496</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dt</span>_compat = v2m_dt_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">497</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.smp</span> = smp_ops(vexpress_smp_ops),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">498</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>_io = v2m_dt_map_io,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">499</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_early = v2m_dt_init_early,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">500</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_irq = v2m_dt_init_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">501</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.timer</span> = &v2m_dt_timer,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">502</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_machine = v2m_dt_init,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">503</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.handle</span>_irq = gic_handle_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">504</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.restart</span> = vexpress_restart,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">505</span> MACHINE_END</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>Linux倡导针对多个SoC、多个电路板的通用DT machine，即一个DT machine的.dt_compat表含多个电路板.dts文件的root结点compatible属性字符串。之后，如果的电路板的初始化序列不一样，可以透过int of_machine_is_compatible(const char *compat) API判断具体的电路板是什么。
譬如arch/arm/mach-exynos/mach-exynos5-dt.c的EXYNOS5_DT machine同时兼容”samsung,exynos5250”和”samsung,exynos5440”：
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">158</span> static char const *exynos5_dt_compat[] __initdata = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">159</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5250"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">160</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5440"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">161</span> NULL
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">162</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">163</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">177</span> DT_MACHINE_START(EXYNOS5_DT, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"SAMSUNG EXYNOS5 (Flattened Device Tree)"</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">178</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* Maintainer: Kukjin Kim <kgene.kim@samsung.com> */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">179</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_irq = exynos5_init_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">180</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.smp</span> = smp_ops(exynos_smp_ops),
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">181</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.map</span>_io = exynos5_dt_map_io,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">182</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.handle</span>_irq = gic_handle_irq,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">183</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_machine = exynos5_dt_machine_init,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">184</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.init</span>_late = exynos_init_late,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">185</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.timer</span> = &exynos4_timer,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">186</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.dt</span>_compat = exynos5_dt_compat,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">187</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.restart</span> = exynos5_restart,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">188</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.reserve</span> = exynos5_reserve,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">189</span> MACHINE_END</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>它的.init_machine成员函数就针对不同的machine进行了不同的分支处理：
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">126</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> __init exynos5_dt_machine_init(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">127</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">128</span> …
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">149</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">150</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_machine_is_compatible(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5250"</span>))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">151</span> of_platform_populate(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>, of_default_bus_match_table,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">152</span> exynos5250_auxdata_lookup, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">153</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">else</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_machine_is_compatible(<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"samsung,exynos5440"</span>))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">154</span> of_platform_populate(<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>, of_default_bus_match_table,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">155</span> exynos5440_auxdata_lookup, <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">156</span> }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li></ul>使用Device Tree后，驱动需要与.dts中描述的设备结点进行匹配，从而引发驱动的probe()函数执行。对于platform_driver而言，需要添加一个OF匹配表，如前文的.dts文件的”acme,a1234-i2c-bus”兼容I2C控制器结点的OF匹配表可以是：
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">436</span> static const struct of_device_id a1234_i2c_of_match[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">437</span> { <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.compatible</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"acme,a1234-i2c-bus "</span>, },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">438</span> {},
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">439</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">440</span> MODULE_DEVICE_TABLE(of, a1234_i2c_of_match)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">441</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">442</span> static struct platform_driver i2c_a1234_driver = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">443</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.driver</span> = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">444</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"a1234-i2c-bus "</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">445</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.owner</span> = THIS_MODULE,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">449</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.of</span>_match_table = a1234_i2c_of_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">450</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">451</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.probe</span> = i2c_a1234_probe,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">452</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.remove</span> = i2c_a1234_remove,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">453</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">454</span> module_platform_driver(i2c_a1234_driver)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>对于I2C和SPI从设备而言，同样也可以透过of_match_table添加匹配的.dts中的相关结点的compatible属性，如sound/soc/codecs/wm8753.c中的：
<code class="hljs avrasm has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1533</span> static const struct of_device_id wm8753_of_match[] = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1534</span> { <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.compatible</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wlf,wm8753"</span>, },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1535</span> { }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1536</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1537</span> MODULE_DEVICE_TABLE(of, wm8753_of_match)<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1587</span> static struct spi_driver wm8753_spi_driver = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1588</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.driver</span> = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1589</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wm8753"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1590</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.owner</span> = THIS_MODULE,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1591</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.of</span>_match_table = wm8753_of_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1592</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1593</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.probe</span> = wm8753_spi_probe,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1594</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.remove</span> = wm8753_spi_remove,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1595</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1640</span> static struct i2c_driver wm8753_i2c_driver = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1641</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.driver</span> = {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1642</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.name</span> = <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"wm8753"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1643</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.owner</span> = THIS_MODULE,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1644</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.of</span>_match_table = wm8753_of_match,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1645</span> },
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1646</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.probe</span> = wm8753_i2c_probe,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1647</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.remove</span> = wm8753_i2c_remove,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1648</span> <span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">.id</span>_table = wm8753_i2c_id,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1649</span> }<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">;</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li></ul>不过这边有一点需要提醒的是，I2C和SPI外设驱动和Device Tree中设备结点的compatible 属性还有一种弱式匹配方法，就是别名匹配。compatible 属性的组织形式为,，别名其实就是去掉compatible 属性中逗号前的manufacturer前缀。关于这一点，可查看drivers/spi/spi.c的源代码，函数spi_match_device()暴露了更多的细节，如果别名出现在设备spi_driver的id_table里面，或者别名与spi_driver的name字段相同，SPI设备和驱动都可以匹配上：
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">90</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> spi_match_device(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device *dev, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_driver *drv)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">91</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">92</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device *spi = to_spi_device(dev);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">93</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_driver *sdrv = to_spi_driver(drv);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">94</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">95</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* Attempt an OF style match */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">96</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_driver_match_device(dev, drv))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">97</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">98</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">99</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">/* Then try ACPI */</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">100</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (acpi_driver_match_device(dev, drv))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">101</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">102</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">103</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (sdrv->id_table)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">104</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> !!spi_match_id(sdrv->id_table, spi);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">105</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">106</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> strcmp(spi->modalias, drv->name) == <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">107</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">71</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device_id *spi_match_id(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device_id *<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">72</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> spi_device *sdev)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">73</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">74</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">while</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>->name[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>]) {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">75</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!strcmp(sdev->modalias, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>->name))
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">76</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">77</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>++;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">78</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">79</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">80</span> }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li></ul>
7、 常用OF API
在Linux的BSP和驱动代码中，还经常会使用到Linux中一组Device Tree的API,这些API通常被冠以of_前缀，它们的实现代码位于内核的drivers/of目录。这些常用的API包括：int of_device_is_compatible(const struct device_node *device,const char *compat);
判断设备结点的compatible 属性是否包含compat指定的字符串。当一个驱动支持2个或多个设备的时候，这些不同.dts文件中设备的compatible 属性都会进入驱动 OF匹配表。因此驱动可以透过Bootloader传递给内核的Device Tree中的真正结点的compatible 属性以确定究竟是哪一种设备，从而根据不同的设备类型进行不同的处理。如drivers/pinctrl/pinctrl-sirf.c即兼容于”sirf,prima2-pinctrl”，又兼容于”sirf,prima2-pinctrl”，在驱动中就有相应分支处理：
<code class="hljs bash has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1682</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_device_is_compatible(np, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"sirf,marco-pinctrl"</span>)) <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1683</span> is_marco = <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>
struct device_node *of_find_compatible_node(struct device_node *from,
const char *type, const char *compatible);
根据compatible属性，获得设备结点。遍历Device Tree中所有的设备结点，看看哪个结点的类型、compatible属性与本函数的输入参数匹配，大多数情况下，from、type为NULL。
int of_property_read_u8_array(const struct device_node *np,
const char *propname, u8 *out_values, size_t sz);
int of_property_read_u16_array(const struct device_node *np,
const char *propname, u16 *out_values, size_t sz);
int of_property_read_u32_array(const struct device_node *np,
const char *propname, u32 *out_values, size_t sz);
int of_property_read_u64(const struct device_node *np, const char
*propname, u64 *out_value);
读取设备结点np的属性名为propname，类型为8、16、32、64位整型数组的属性。对于32位处理器来讲，最常用的是of_property_read_u32_array()。如在arch/arm/mm/cache-l2x0.c中，透过如下语句读取L2 cache的”arm,data-latency”属性：
<code class="hljs haskell has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">534</span> of_property_read_u32_array(np, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,data-latency"</span>, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">535</span> <span class="hljs-typedef" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">data</span>, <span class="hljs-type" style="box-sizing: border-box; color: rgb(102, 0, 102);">ARRAY_SIZE</span><span class="hljs-container" style="box-sizing: border-box;">(<span class="hljs-title" style="box-sizing: border-box;">data</span>)</span>);</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li></ul>
在arch/arm/boot/dts/vexpress-v2p-ca9.dts中，含有”arm,data-latency”属性的L2 cache结点如下：
<code class="hljs lasso has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">137</span> L2: <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">cache</span><span class="hljs-attribute" style="box-sizing: border-box;">-controller</span>@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1e00</span>a000 {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">138</span> compatible <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"arm,pl310-cache"</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">139</span> reg <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1e00a000</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0x1000</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">140</span> interrupts <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">43</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">4</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">141</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">cache</span><span class="hljs-attribute" style="box-sizing: border-box;">-level</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">142</span> arm,<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">data</span><span class="hljs-attribute" style="box-sizing: border-box;">-latency</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">143</span> arm,<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">tag</span><span class="hljs-attribute" style="box-sizing: border-box;">-latency</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">=</span> <span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;"><</span><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span><span class="hljs-subst" style="color: rgb(0, 0, 0); box-sizing: border-box;">></span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">144</span> }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>有些情况下，整形属性的长度可能为1，于是内核为了方便调用者，又在上述API的基础上封装出了更加简单的读单一整形属性的API，它们为int of_property_read_u8()、of_property_read_u16()等，实现于include/linux/of.h：
<code class="hljs rust has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">513</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> inline <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> of_property_read_u8(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">514</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *propname,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">515</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">u8</span> *out_value)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">516</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">517</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> of_property_read_u8_array(np, propname, out_value, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">518</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">519</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">520</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> inline <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> of_property_read_u16(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">521</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *propname,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">522</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">u16</span> *out_value)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">523</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">524</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> of_property_read_u16_array(np, propname, out_value, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">525</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">526</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">527</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> inline <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> of_property_read_u32(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">528</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *propname,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">529</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">u32</span> *out_value)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">530</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">531</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> of_property_read_u32_array(np, propname, out_value, <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">532</span> }</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li></ul>int of_property_read_string(struct device_node *np, const char
*propname, const char **out_string);
int of_property_read_string_index(struct device_node *np, const char
*propname, int index, const char **output);
前者读取字符串属性，后者读取字符串数组属性中的第index个字符串。如drivers/clk/clk.c中的of_clk_get_parent_name()透过of_property_read_string_index()遍历clkspec结点的所有”clock-output-names”字符串数组属性。
<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-radius: 0px; word-wrap: normal; background: transparent;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1759</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *of_clk_get_parent_name(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> device_node *np, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> index)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1760</span> {
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1761</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> of_phandle_args clkspec;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1762</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> *clk_name;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1763</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> rc;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1764</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1765</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (index < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1766</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1767</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1768</span> rc = of_parse_phandle_with_args(np, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"clocks"</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"#clock-cells"</span>, index,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1769</span> &clkspec);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1770</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (rc)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1771</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">NULL</span>;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1772</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1773</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (of_property_read_string_index(clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.np</span>, <span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"clock-output-names"</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1774</span> clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.args_count</span> ? clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.args</span>[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>] : <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>,
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1775</span> &clk_name) < <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>)
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1776</span> clk_name = clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.np</span>->name;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1777</span>
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1778</span> of_node_put(clkspec<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.np</span>);
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1779</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> clk_name;
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1780</span> }
<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1781</span> EXPORT_SYMBOL_GPL(of_clk_get_parent_name);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right; background-color: rgb(238, 238, 238);"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li></ul>static inline bool of_property_read_bool(const struct device_node *np,
const char *propname);
如果设备结点np含有propname属性，则返回true，否则返回false。一般用于检查空属性是否存在。
void __iomem *of_iomap(struct device_node *node, int index);
通过设备结点直接进行设备内存区间的 ioremap()，index是内存段的索引。若设备结点的reg属性有多段，可通过index标示要ioremap的是哪一段，只有1段的情况，index为0。采用Device Tree后，大量的设备驱动通过of_iomap()进行映射，而不再通过传统的ioremap。
unsigned int irq_of_parse_and_map(struct device_node *dev, int index);
透过Device Tree或者设备的中断号，实际上是从.dts中的interrupts属性解析出中断号。若设备使用了多个中断，index指定中断的索引号。
还有一些OF API，这里不一一列举，具体可参考include/linux/of.h头文件。
8、总结
ARM社区一贯充斥的大量垃圾代码导致Linus盛怒，因此社区在2011年到2012年进行了大量的工作。ARM Linux开始围绕Device Tree展开，Device Tree有自己的独立的语法，它的源文件为.dts，编译后得到.dtb，Bootloader在引导Linux内核的时候会将.dtb地址告知内核。之后内核会展开Device Tree并创建和注册相关的设备，因此arch/arm/mach-xxx和arch/arm/plat-xxx中大量的用于注册platform、I2C、SPI板级信息的代码被删除，而驱动也以新的方式和.dts中定义的设备结点进行匹配。
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