Documentation-spi-pxa2xx.txt

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Documentation-spi-pxa2xx.txt的中文翻译

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中文版维护者： 马建刚 majg <1519014266@qq.com>

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1 PXA2xx SPI on SSP driver HOWTO

-SSP 上的PXA2XX SPI驱动HOWTO

2 ===================================================

3 This a mini howto on the pxa2xx_spi driver. The driver turns a PXA2xx

4 synchronous serial port into a SPI master controller

5 (see Documentation/spi/spi-summary). The driver has the following features

-这是一个微型的HOWTO上pxa2xx_spi驱动。驱动转动一个PXA2XX的同步串行端口

到一个SPI主控制器（见Documentation/spi/spi-summary）。该驱动器具有以下功能

6

7 - Support for any PXA2xx SSP

8 - SSP PIO and SSP DMA data transfers.

9 - External and Internal (SSPFRM) chip selects.

10 - Per slave device (chip) configuration.

11 - Full suspend, freeze, resume support.

12

13 The driver is built around a "spi_message" fifo serviced by workqueue and a

14 tasklet. The workqueue, "pump_messages", drives message fifo and the tasklet

15 (pump_transfer) is responsible for queuing SPI transactions and setting up and

16 launching the dma/interrupt driven transfers.

-该驱动程序是围绕一个“spi_message”先进先出服务工作队列和一个tasklet。

工作队列“pump_messages”，带动消息FIFO和这个tasklet（pump_transfer）

排队SPI交易负责建立和启动DMA /中断驱动的传输。

17

18 Declaring PXA2xx Master Controllers

-声明PXA2XX主控制器

19 -----------------------------------

20 Typically a SPI master is defined in the arch/.../mach-*/board-*.c as a

21 "platform device". The master configuration is passed to the driver via a table

22 found in include/linux/spi/pxa2xx_spi.h:

-通常情况下，SPI定义在arch/.../mach-*/board-*.c视为一个“platform device”。

主配置被传递到驱动程序通过一个表在include/linux/spi/pxa2xx_spi.h：

23

24 struct pxa2xx_spi_master {

25 u32 clock_enable;

26 u16 num_chipselect;

27 u8 enable_dma;

28 };

29

30 The "pxa2xx_spi_master.clock_enable" field is used to enable/disable the

31 corresponding SSP peripheral block in the "Clock Enable Register (CKEN"). See

32 the "PXA2xx Developer Manual" section "Clocks and Power Management".

-的“pxa2xx_spi_master.clock_enable”字段用于启用/禁用相应的SSP外设模块中的

“时钟使能寄存器（CKEN”）。请参阅“PXA2XX开发手册”一节“时钟和电源管理”。

33

34 The "pxa2xx_spi_master.num_chipselect" field is used to determine the number of

35 slave device (chips) attached to this SPI master.

-"pxa2xx_spi_master.num_chipselect"字段用于确定连接到SPI主从设备的数量（筹）。

36

37 The "pxa2xx_spi_master.enable_dma" field informs the driver that SSP DMA should

38 be used. This caused the driver to acquire two DMA channels: rx_channel and

39 tx_channel. The rx_channel has a higher DMA service priority the tx_channel.

40 See the "PXA2xx Developer Manual" section "DMA Controller".

-“pxa2xx_spi_master.enable_dma”字段通知SSP DMA的驱动程序应该被使用。

这导致驱动购入两个DMA通道：rx_channel和tx_channel。 rx_channel具有

更高的DMA服务优先tx_channel。请参阅的“PXA2XX开发者手册”一节中的“DMA控制器”。

41

42 NSSP MASTER SAMPLE

43 ------------------

44 Below is a sample configuration using the PXA255 NSSP.

-下面是一个使用PXA255的NSSP的示例配置。

45

46 static struct resource pxa_spi_nssp_resources[] = {

47 [0] = {

48 .start = __PREG(SSCR0_P(2)), /* Start address of NSSP */

49 .end = __PREG(SSCR0_P(2)) + 0x2c, /* Range of registers */

50 .flags = IORESOURCE_MEM,

51 },

52 [1] = {

53 .start = IRQ_NSSP, /* NSSP IRQ */

54 .end = IRQ_NSSP,

55 .flags = IORESOURCE_IRQ,

56 },

57 };

58

59 static struct pxa2xx_spi_master pxa_nssp_master_info = {

60 .clock_enable = CKEN_NSSP, /* NSSP Peripheral clock */

61 .num_chipselect = 1, /* Matches the number of chips attached to NSSP */

62 .enable_dma = 1, /* Enables NSSP DMA */

63 };

64

65 static struct platform_device pxa_spi_nssp = {

66 .name = "pxa2xx-spi", /* MUST BE THIS VALUE, so device match driver */

67 .id = 2, /* Bus number, MUST MATCH SSP number 1..n */

68 .resource = pxa_spi_nssp_resources,

69 .num_resources = ARRAY_SIZE(pxa_spi_nssp_resources),

70 .dev = {

71 .platform_data = &pxa_nssp_master_info, /* Passed to driver */

72 },

73 };

74

75 static struct platform_device *devices[] __initdata = {

76 &pxa_spi_nssp,

77 };

78

79 static void __init board_init(void)

80 {

81 (void)platform_add_device(devices, ARRAY_SIZE(devices));

82 }

83

84 Declaring Slave Devices

-声明从设备

85 -----------------------

86 Typically each SPI slave (chip) is defined in the arch/.../mach-*/board-*.c

87 using the "spi_board_info" structure found in "linux/spi/spi.h". See

88 "Documentation/spi/spi-summary" for additional information.

-通常，每个SPI从器件（芯片）在aarch/.../mach-*/board-*.c使用 "spi_board_info"

发现"linux/spi/spi.h"结构。请参阅“文档/ SPI/ SPI摘要”​​的其他信息。

89

90 Each slave device attached to the PXA must provide slave specific configuration

91 information via the structure "pxa2xx_spi_chip" found in

92 "include/linux/spi/pxa2xx_spi.h". The pxa2xx_spi master controller driver

93 will uses the configuration whenever the driver communicates with the slave

94 device. All fields are optional.

-每个从设备必须连接到PXA提供从具体的配置信息通过结构“pxa2xx_spi_chip”中发现“include/linux/spi/pxa2xx_spi.h”。

pxa2xx_spi主控制器驱动程序将使用配置时，从设备驱动程序通信。所有字段是可选的。

95

96 struct pxa2xx_spi_chip {

97 u8 tx_threshold;

98 u8 rx_threshold;

99 u8 dma_burst_size;

100 u32 timeout;

101 u8 enable_loopback;

102 void (*cs_control)(u32 command);

103 };

104

105 The "pxa2xx_spi_chip.tx_threshold" and "pxa2xx_spi_chip.rx_threshold" fields are

106 used to configure the SSP hardware fifo. These fields are critical to the

107 performance of pxa2xx_spi driver and misconfiguration will result in rx

108 fifo overruns (especially in PIO mode transfers). Good default values are

-“pxa2xx_spi_chip.tx_threshold”和的“pxa2xx_spi_chip.rx_threshold”字段是用来配置SSP的硬件fifo。

这些领域是至关重要的性能的pxa2xx_spi驱动程序和配置错误会导致在RX FIFO溢出（尤其是在PIO模式传输）。

良好的默认值是

109

110 .tx_threshold = 8,

111 .rx_threshold = 8,

112

113 The range is 1 to 16 where zero indicates "use default".

-范围是1到16，其中零表示"use default"。

114

115 The "pxa2xx_spi_chip.dma_burst_size" field is used to configure PXA2xx DMA

116 engine and is related the "spi_device.bits_per_word" field. Read and understand

117 the PXA2xx "Developer Manual" sections on the DMA controller and SSP Controllers

118 to determine the correct value. An SSP configured for byte-wide transfers would

119 use a value of 8. The driver will determine a reasonable default if

120 dma_burst_size == 0.

-“pxa2xx_spi_chip.dma_burst_size”字段是用来配置PXA2XX DMA引擎是有关在“spi_device.bits_per_word字段。

阅读并理解“PXA2XX开发者手册”章节DMA控制器和SSP控制器，以确定正确的值。字节宽的传输配置一个SSP将使

用值8。如果dma_burst_size== 0驱动程序将确定一个合理的默认情况。

121

122 The "pxa2xx_spi_chip.timeout" fields is used to efficiently handle

123 trailing bytes in the SSP receiver fifo. The correct value for this field is

124 dependent on the SPI bus speed ("spi_board_info.max_speed_hz") and the specific

125 slave device. Please note that the PXA2xx SSP 1 does not support trailing byte

126 timeouts and must busy-wait any trailing bytes.

-“pxa2xx_spi_chip.timeout”字段是用来有效地处理尾随字节在SSP接收FIFO。

此字段的正确值依赖于SPI总线速度（的“spi_board_info.max_speed_hz”）和

特定的从设备。请注意SSP1 PXA2XX不支持尾随字节超时，必须忙等待任何尾随字节。

127

128 The "pxa2xx_spi_chip.enable_loopback" field is used to place the SSP porting

129 into internal loopback mode. In this mode the SSP controller internally

130 connects the SSPTX pin to the SSPRX pin. This is useful for initial setup

131 testing.

-“pxa2xx_spi_chip.enable_loopback”字段是用来放置SSP进入内部环回模式移植。

在这种模式下SSP控制器内部连接SSPTX的的针到SSPRX引脚。初始设置测试是非常有用的。

132

133 The "pxa2xx_spi_chip.cs_control" field is used to point to a board specific

134 function for asserting/deasserting a slave device chip select. If the field is

135 NULL, the pxa2xx_spi master controller driver assumes that the SSP port is

136 configured to use SSPFRM instead.

-“pxa2xx_spi_chip.cs_control”字段是用来指向板子特定功能的asserting/deasserting从器件芯片选择。

如果该字段是NULL，pxa2xx_spi的主控制器驱动程序假定SSP端口的配置为使用SSPFRM。

137

138 NOTE: the SPI driver cannot control the chip select if SSPFRM is used, so the

139 chipselect is dropped after each spi_transfer. Most devices need chip select

140 asserted around the complete message. Use SSPFRM as a GPIO (through cs_control)

141 to accommodate these chips.

-注意：SPI驱动程序无法控制芯片选择如果使用SSPFRM，所以片选后，每个spi_transfer下降。

大多数设备需要芯片选择断言围绕完整的消息。使用SSPFRM作为一个GPIO（通过cs_control）以适应这些芯片。

142

143

144 NSSP SLAVE SAMPLE

145 -----------------

146 The pxa2xx_spi_chip structure is passed to the pxa2xx_spi driver in the

147 "spi_board_info.controller_data" field. Below is a sample configuration using

148 the PXA255 NSSP.

-pxa2xx_spi_chip结构被传递给在pxa2xx_spi驱动所在的“spi_board_info.controller_data”字段。

下面是一个使用PXA255的NSSP示例配置。

149

150 /* Chip Select control for the CS8415A SPI slave device */

151 static void cs8415a_cs_control(u32 command)

152 {

153 if (command & PXA2XX_CS_ASSERT)

154 GPCR(2) = GPIO_bit(2);

155 else

156 GPSR(2) = GPIO_bit(2);

157 }

158

159 /* Chip Select control for the CS8405A SPI slave device */

160 static void cs8405a_cs_control(u32 command)

161 {

162 if (command & PXA2XX_CS_ASSERT)

163 GPCR(3) = GPIO_bit(3);

164 else

165 GPSR(3) = GPIO_bit(3);

166 }

167

168 static struct pxa2xx_spi_chip cs8415a_chip_info = {

169 .tx_threshold = 8, /* SSP hardward FIFO threshold */

170 .rx_threshold = 8, /* SSP hardward FIFO threshold */

171 .dma_burst_size = 8, /* Byte wide transfers used so 8 byte bursts */

172 .timeout = 235, /* See Intel documentation */

173 .cs_control = cs8415a_cs_control, /* Use external chip select */

174 };

175

176 static struct pxa2xx_spi_chip cs8405a_chip_info = {

177 .tx_threshold = 8, /* SSP hardward FIFO threshold */

178 .rx_threshold = 8, /* SSP hardward FIFO threshold */

179 .dma_burst_size = 8, /* Byte wide transfers used so 8 byte bursts */

180 .timeout = 235, /* See Intel documentation */

181 .cs_control = cs8405a_cs_control, /* Use external chip select */

182 };

183

184 static struct spi_board_info streetracer_spi_board_info[] __initdata = {

185 {

186 .modalias = "cs8415a", /* Name of spi_driver for this device */

187 .max_speed_hz = 3686400, /* Run SSP as fast a possbile */

188 .bus_num = 2, /* Framework bus number */

189 .chip_select = 0, /* Framework chip select */

190 .platform_data = NULL; /* No spi_driver specific config */

191 .controller_data = &cs8415a_chip_info, /* Master chip config */

192 .irq = STREETRACER_APCI_IRQ, /* Slave device interrupt */

193 },

194 {

195 .modalias = "cs8405a", /* Name of spi_driver for this device */

196 .max_speed_hz = 3686400, /* Run SSP as fast a possbile */

197 .bus_num = 2, /* Framework bus number */

198 .chip_select = 1, /* Framework chip select */

199 .controller_data = &cs8405a_chip_info, /* Master chip config */

200 .irq = STREETRACER_APCI_IRQ, /* Slave device interrupt */

201 },

202 };

203

204 static void __init streetracer_init(void)

205 {

206 spi_register_board_info(streetracer_spi_board_info,

207 ARRAY_SIZE(streetracer_spi_board_info));

208 }

209

210

211 DMA and PIO I/O Support

212 -----------------------

213 The pxa2xx_spi driver supports both DMA and interrupt driven PIO message

214 transfers. The driver defaults to PIO mode and DMA transfers must be enabled

215 by setting the "enable_dma" flag in the "pxa2xx_spi_master" structure. The DMA

216 mode supports both coherent and stream based DMA mappings.

-pxa2xx_spi驱动程序支持DMA和中断驱动的PIO传输信息。这个驱动程序默认为PIO模式和DMA传输，

必须启用通过“pxa2xx_spi_master”结构的“enable_dma”标志设置。DMA模式的支持连贯和基于流DMA映射。

217

218 The following logic is used to determine the type of I/O to be used on

219 a per "spi_transfer" basis:

-使用以下逻辑I / O的每一个的“spi_transfer”基础上使用的类型来确定：

220

221 if !enable_dma then

222 always use PIO transfers

223

224 if spi_message.len > 8191 then

225 print "rate limited" warning

226 use PIO transfers

227

228 if spi_message.is_dma_mapped and rx_dma_buf != 0 and tx_dma_buf != 0 then

229 use coherent DMA mode

230

231 if rx_buf and tx_buf are aligned on 8 byte boundary then

232 use streaming DMA mode

233

234 otherwise

235 use PIO transfer

236

237 THANKS TO

238 ---------

239

240 David Brownell and others for mentoring the development of this driver.

241