【linux设备模型】之platform设备驱动

一、platform总线、设备和驱动platform是一种虚拟总线，相应的设备称为platform_device，相应的驱动称为platform_driver。platform_device定义在<linux/platform_device.h>中：

1 struct platform_device {
2     const char    * name;
3     int        id;
4     struct device    dev;
5     u32        num_resources;
6     struct resource    * resource;
7
8     const struct platform_device_id    *id_entry;
9
10     /* arch specific additions */
11     struct pdev_archdata    archdata;
12 };

其中的resource是platform驱动用到的资源，它是定义在<include/linux/ioport.h>中：

1 struct resource {
2     resource_size_t start;
3     resource_size_t end;
4     const char *name;
5     unsigned long flags;
6     struct resource *parent, *sibling, *child;
7 };

platform_driver定义在<linux/platform_device.h>中：

1 struct platform_driver {
2     int (*probe)(struct platform_device *);
3     int (*remove)(struct platform_device *);
4     void (*shutdown)(struct platform_device *);
5     int (*suspend)(struct platform_device *, pm_message_t state);
6     int (*resume)(struct platform_device *);
7     struct device_driver driver;
8     const struct platform_device_id *id_table;
9 };

系统中为platform总线定义了一个实例platform_bus_type，在<linux/platform_device.h>进行了声明：

extern struct bus_type platform_bus_type;
定义在drivers/base/platform.c中：

1 struct bus_type platform_bus_type = {
2     .name        = "platform",
3     .dev_attrs    = platform_dev_attrs,
4     .match        = platform_match,
5     .uevent        = platform_uevent,
6     .pm        = &platform_dev_pm_ops,
7 };
8 EXPORT_SYMBOL_GPL(platform_bus_type);

二、具体实现

1、platform_match函数的实现（定义在drivers/base/platform.c中）：

1 static const struct platform_device_id *platform_match_id(
2             const struct platform_device_id *id,
3             struct platform_device *pdev)
4 {
5     while (id->name[0]) {
6         if (strcmp(pdev->name, id->name) == 0) {
7             pdev->id_entry = id;
8             return id;
9         }
10         id++;
11     }
12     return NULL;
13 }
14
15 /**
16  * platform_match - bind platform device to platform driver.
17  * @dev: device.
18  * @drv: driver.
19  *
20  * Platform device IDs are assumed to be encoded like this:
21  * "<name><instance>", where <name> is a short description of the type of
22  * device, like "pci" or "floppy", and <instance> is the enumerated
23  * instance of the device, like '0' or '42'.  Driver IDs are simply
24  * "<name>".  So, extract the <name> from the platform_device structure,
25  * and compare it against the name of the driver. Return whether they match
26  * or not.
27  */
28 static int platform_match(struct device *dev, struct device_driver *drv)
29 {
30     struct platform_device *pdev = to_platform_device(dev);
31     struct platform_driver *pdrv = to_platform_driver(drv);
32
33     /* Attempt an OF style match first */
34     if (of_driver_match_device(dev, drv))
35         return 1;
36
37     /* Then try to match against the id table */
38     if (pdrv->id_table)
39         return platform_match_id(pdrv->id_table, pdev) != NULL;
40
41     /* fall-back to driver name match */
42     return (strcmp(pdev->name, drv->name) == 0);
43 }

是通过device的name和driver的name进行匹配的。

2、platform_device的定义和注册

（platform_add_devices定义在drivers/base/platform.c中）

1 /**
2  * platform_add_devices - add a numbers of platform devices
3  * @devs: array of platform devices to add
4  * @num: number of platform devices in array
5  */
6 int platform_add_devices(struct platform_device **devs, int num)
7 {
8     int i, ret = 0;
9
10     for (i = 0; i < num; i++) {
11         ret = platform_device_register(devs[i]);
12         if (ret) {
13             while (--i >= 0)
14                 platform_device_unregister(devs[i]);
15             break;
16         }
17     }
18
19     return ret;
20 }
21 EXPORT_SYMBOL_GPL(platform_add_devices);

对于一个指定的板子来说，比如对于ldd6410的globalfifo驱动来说，要在mach-ldd6410.c中定义platform_device globalfifo_device,并将globalfifo_device放入ldd6410_devices数组中，代码如下所示。

3、platform_driver的操作

platform_driver的定义和注册在相应驱动文件中实现，下面是《linux驱动开发详解》一书中globalfifo的例子的部分代码：

4、platform设备资源和数据

（1）、resource的定义（<linux/ioport.h>）

1 struct resource {

2     resource_size_t start;
3     resource_size_t end;
4     const char *name;
5     unsigned long flags;
6     struct resource *parent, *sibling, *child;
7 };

当flags是IORESOURCE_MEM时，start和end分别是资源的起始地址和结束地址；

当flags是IORESOURCE_IRQ时，start和end分别是资源的起始中断号和结束中断号；

#define IORESOURCE_TYPE_BITS    0x00001f00    /* Resource type */
#define IORESOURCE_IO         0x00000100
#define IORESOURCE_MEM        0x00000200
#define IORESOURCE_IRQ        0x00000400
#define IORESOURCE_DMA        0x00000800
#define IORESOURCE_BUS        0x00001000

对于同种类型的资源可以有两份或多份。

（2）、获得资源

对resource的定义通常在板文件中，而驱动通过platform_get_resource获得资源（driver/base/platform.c）：

1 /**
2  * platform_get_resource - get a resource for a device
3  * @dev: platform device
4  * @type: resource type
5  * @num: resource index
6  */
7 struct resource *platform_get_resource(struct platform_device *dev,
8                        unsigned int type, unsigned int num)
9 {
10     int i;
11
12     for (i = 0; i < dev->num_resources; i++) {
13         struct resource *r = &dev->resource[i];
14
15         if (type == resource_type(r) && num-- == 0)
16             return r;
17     }
18     return NULL;
19 }
20 EXPORT_SYMBOL_GPL(platform_get_resource);

三、platform驱动的一个例子

以linux-2.6.38内核的dm9000驱动为例说明平台驱动的定义和资源获取。

1、platform_device和resource的定义（mach-mini6410.c）

 1 /* DM9000AEP 10/100 ethernet controller */2 /*dm9000的资源*/3 static struct resource mini6410_dm9k_resource[] = {4     [0] = {5         .start    = S3C64XX_PA_XM0CSN1,6         .end    = S3C64XX_PA_XM0CSN1 + 1,7         .flags    = IORESOURCE_MEM8     },9     [1] = {10         .start    = S3C64XX_PA_XM0CSN1 + 4,11         .end    = S3C64XX_PA_XM0CSN1 + 5,12         .flags    = IORESOURCE_MEM13     },14     [2] = {15         .start    = S3C_EINT(7),16         .end    = S3C_EINT(7),17         .flags    = IORESOURCE_IRQ | IORESOURCE_IRQ_HIGHLEVEL18     }19 };20 /*dm9000_plat_data定义在<linux/dm9000.h>*/21 static struct dm9000_plat_data mini6410_dm9k_pdata = {22     .flags        = (DM9000_PLATF_16BITONLY | DM9000_PLATF_NO_EEPROM),23 };2425 static struct platform_device mini6410_device_eth = {26     .name        = "dm9000",27     .id        = -1,28     .num_resources    = ARRAY_SIZE(mini6410_dm9k_resource),29     .resource    = mini6410_dm9k_resource,30     .dev        = {31         .platform_data    = &mini6410_dm9k_pdata,32     },33 };3435 /*所有的设备存放在这个数组里，最后通过platform_add_devices进行注册*/36 static struct platform_device *mini6410_devices[] __initdata = {37     &mini6410_device_eth,38     &s3c_device_hsmmc0,39     &s3c_device_hsmmc1,40     &s3c_device_ohci,41     &s3c_device_nand,42     &s3c_device_fb,43     &mini6410_lcd_powerdev,44     &s3c_device_adc,45     &s3c_device_ts,46 };

2、platform_driver的定义和注册（dm9000.c）

 1 static struct platform_driver dm9000_driver = {2     .driver    = {3         .name    = "dm9000",4         .owner     = THIS_MODULE,5         .pm     = &dm9000_drv_pm_ops,6     },7     .probe   = dm9000_probe,8     .remove  = __devexit_p(dm9000_drv_remove),9 };1011 static int __init12 dm9000_init(void)13 {14     printk(KERN_INFO "%s Ethernet Driver, V%s\n", CARDNAME, DRV_VERSION);1516     return platform_driver_register(&dm9000_driver);17 }1819 static void __exit20 dm9000_cleanup(void)21 {22     platform_driver_unregister(&dm9000_driver);23 }

dm9000驱动获得定义在板文件中的platform_data的方法：

struct platform_device *pdev

struct  dm9000_plat_data *pdata = pdev->dev.platform_data;

db->addr_res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

db->data_res = platform_get_resource(pdev, IORESOURCE_MEM, 1);

db->irq_res  = platform_get_resource(pdev, IORESOURCE_IRQ, 0);

platform_get_resource函数定义在drivers/base/platform.c中：

1 /**
2  * platform_get_resource - get a resource for a device
3  * @dev: platform device
4  * @type: resource type
5  * @num: resource index
6  */
7 struct resource *platform_get_resource(struct platform_device *dev,
8                        unsigned int type, unsigned int num)
9 {
10     int i;
11
12     for (i = 0; i < dev->num_resources; i++) {
13         struct resource *r = &dev->resource[i];
14
15         if (type == resource_type(r) && num-- == 0)
16             return r;
17     }
18     return NULL;
19 }
20 EXPORT_SYMBOL_GPL(platform_get_resource);

参考：《linux驱动开发详解》