基於S3C2440的嵌入式Linux驅動——SPI子系統解讀（一）

本文將介紹SPI子系統。內核版本為2.6.30。如有錯誤歡迎指正。

預備知識要求：1.SPI總線

2. platfrom平台

3. sysfs子系統

4. 閱讀過LDD3第3，5，6，7，9，10，11章的內容。

NOTE：如果沒有看過LDD3的相關內容，直接看內核源碼將非常吃力！！！

PC主機：Ubuntu 和 RedHat 9.0

目標板：TQ2440開發板 cpu:s3c2440 linux內核:2.6.30

0.引言

本系列文章對Linux設備模型中的SPI子系統進行講解。SPI子系統的講解將分為4個部分。

第一部分，即本篇文章，將對SPI子系統整體進行描述，同時給出SPI的相關數據結構，最後描述SPI總線的注冊。

第二部分，該文將對SPI的主控制器(master)驅動進行描述。
基於S3C2440的嵌入式Linux驅動——SPI子系統解讀（二）http://www.linuxidc.com/Linux/2012-08/68404.htm

第三部分，該文將對SPI設備驅動，也稱protocol 驅動，進行講解。
基於S3C2440的嵌入式Linux驅動——SPI子系統解讀（三）http://www.linuxidc.com/Linux/2012-08/68405.htm

第四部分，通過SPI設備驅動留給用戶層的API，我們將從上到下描述數據是如何通過SPI的protocol 驅動，由bitbang中轉，最後由master驅動將數據傳輸出去。

基於S3C2440的嵌入式Linux驅動——SPI子系統解讀（四）http://www.linuxidc.com/Linux/2012-08/68406.htm

1.SPI子系統綜述

SPI子系統從上到下分為：spi設備驅動層，核心層和master驅動層。其中master驅動抽象出spi控制器的相關操作，而spi設備驅動層抽象出了用戶空間API。

platform_device結構中描述了SPI控制器的相關資源，同時在板級信息中將會添加spi設備的相關信息。master驅動將以platform_driver形式體現出來，也就是說

在主控制器(master)和主控制器驅動將掛載到platform總線上。platform_driver的probe函數中將注冊spi_master，同時將會獲取在板級信息中添加的spi設備，將該

信息轉換成spi_device，然後注冊spi_device到spi總線上。spi_driver結構用於描述spi設備驅動，也將掛載到spi總線上。連同spi_driver一起注冊的是字符設備，該

字符設備將提供5個API給用戶空間。通過API，用戶空間可以執行半雙工讀、半雙工寫和全雙工讀寫。

2. SPI的相關數據結構

這裡將介紹內核所用到的關鍵數據結構，還有些結構將在用到時加以說明。

2.1 spi_master

該結構用於描述SOC的SPI控制器，S3C2440共有兩個SPI控制器。

1. /**
2. * struct spi_master - interface to SPI master controller
3. * @dev: device interface to this driver
4. * @bus_num: board-specific (and often SOC-specific) identifier for a
5. * given SPI controller.
6. * @num_chipselect: chipselects are used to distinguish individual
7. * SPI slaves, and are numbered from zero to num_chipselects.
8. * each slave has a chipselect signal, but it's common that not
9. * every chipselect is connected to a slave.
10. * @dma_alignment: SPI controller constraint on DMA buffers alignment.
11. * @setup: updates the device mode and clocking records used by a
12. * device's SPI controller; protocol code may call this. This
13. * must fail if an unrecognized or unsupported mode is requested.
14. * It's always safe to call this unless transfers are pending on
15. * the device whose settings are being modified.
16. * @transfer: adds a message to the controller's transfer queue.
17. * @cleanup: frees controller-specific state
18. *
19. * Each SPI master controller can communicate with one or more @spi_device
20. * children. These make a small bus, sharing MOSI, MISO and SCK signals
21. * but not chip select signals. Each device may be configured to use a
22. * different clock rate, since those shared signals are ignored unless
23. * the chip is selected.
24. *
25. * The driver for an SPI controller manages access to those devices through
26. * a queue of spi_message transactions, copying data between CPU memory and
27. * an SPI slave device. For each such message it queues, it calls the
28. * message's completion function when the transaction completes.
29. */
30. struct spi_master {
31. struct device dev;
33. /* other than negative (== assign one dynamically), bus_num is fully
34. * board-specific. usually that simplifies to being SOC-specific.
35. * example: one SOC has three SPI controllers, numbered 0..2,
36. * and one board's schematics might show it using SPI-2. software
37. * would normally use bus_num=2 for that controller.
38. */
39. s16 bus_num;
41. /* chipselects will be integral to many controllers; some others
42. * might use board-specific GPIOs.
43. */
44. u16 num_chipselect; //該值不能為0，否則會注冊失敗
46. /* some SPI controllers pose alignment requirements on DMAable
47. * buffers; let protocol drivers know about these requirements.
48. */
49. u16 dma_alignment;
51. /* Setup mode and clock, etc (spi driver may call many times).
52. *
53. * IMPORTANT: this may be called when transfers to another
54. * device are active. DO NOT UPDATE SHARED REGISTERS in ways
55. * which could break those transfers.
56. */
57. int (*setup)(struct spi_device *spi);
59. /* bidirectional bulk transfers
60. *
61. * + The transfer() method may not sleep; its main role is
62. * just to add the message to the queue.
63. * + For now there's no remove-from-queue operation, or
64. * any other request management
65. * + To a given spi_device, message queueing is pure fifo
66. *
67. * + The master's main job is to process its message queue,
68. * selecting a chip then transferring data
69. * + If there are multiple spi_device children, the i/o queue
70. * arbitration algorithm is unspecified (round robin, fifo,
71. * priority, reservations, preemption, etc)
72. *
73. * + Chipselect stays active during the entire message
74. * (unless modified by spi_transfer.cs_change != 0).
75. * + The message transfers use clock and SPI mode parameters
76. * previously established by setup() for this device
77. */
78. int (*transfer)(struct spi_device *spi,
79. struct spi_message *mesg);
81. /* called on release() to free memory provided by spi_master */
82. void (*cleanup)(struct spi_device *spi);
83. };