Linux下DM644x設備驅動I2C之總線驅動

Linux DM6441下I2C設備驅動的開發 和常用的Linux I2C的驅動開發一樣，主要包括總線Bus驅動，以及相應的設備驅動開發。 總線驅動和CPU的關系較為密切，涉及到相關硬件的操作。 本文以Linux2.6.1和Dm6441簡單解析一下整個驅動的編寫架構。 1. 總線驅動 涉及到總線驅動的相關代碼在drivers/i2c/bussses下面，該目錄下是各CPU的I2C模塊涉及到的內容，這裡我們選擇i2c-davinci.c文件 總線驅動中Init函數i2c_davinci_init如下：

1. static int __init i2c_davinci_init(void)
2. {
3. int status;
4. struct device *dev = NULL;
6. DEB0("%s %s", __TIME__, __DATE__);
8. DEB1("i2c_davinci_init()");
10. #if 0
11. if (i2c_davinci_busFreq > 200)
12. i2c_davinci_busFreq = 400; /*Fast mode */
13. else
14. i2c_davinci_busFreq = 100; /*Standard mode */
15. #endif
17. i2c_clock = clk_get (dev, "I2CCLK"); //獲取I2C輸入時鐘批頻率27MHz
19. if (IS_ERR(i2c_clock))
20. return -1;
22. clk_use (i2c_clock);
23. clk_enable (i2c_clock);
24. i2c_davinci_inputClock = clk_get_rate (i2c_clock); //獲取I2C輸入時鐘批頻率27MHz
26. DEB1 ("IP CLOCK = %ld", i2c_davinci_inputClock);
28. memset(&i2c_davinci_dev, 0, sizeof(i2c_davinci_dev));
29. init_waitqueue_head(&i2c_davinci_dev.cmd_wait);
31. i2c_davinci_dev.regs = (davinci_i2cregsovly)I2C_BASE; //I2C控制器相關寄存器所在地址
33. status = (int)request_region(I2C_BASE, I2C_IOSIZE, MODULE_NAME); //申請一塊IO輸入輸出區域#define MODULE_NAME "DaVinci I2C"
34. if (!status) {
35. i2c_err("I2C is already in use\n");
36. return -ENODEV;
37. }
39. status = request_irq(IRQ_I2C, i2c_davinci_isr, 0, "i2c",
40. &i2c_davinci_dev); //申請I2C中斷號IRQ_I2C=39
41. if (status) {
42. i2c_err("failed to request I2C IRQ");
43. goto do_release_region;
44. }
46. i2c_set_adapdata(&i2c_davinci_adap, &i2c_davinci_dev); //adap設備的驅動程序私有數據i2c_davinci_adap->dev->driver_data =i2c_davinci_dev
47. status = i2c_add_adapter(&i2c_davinci_adap); //I2C上添加adapter
48. if (status) {
49. i2c_err("failed to add adapter");
50. goto do_free_irq;
51. }
53. i2c_davinci_reset(&i2c_davinci_dev); //完成I2C相關寄存器的初始化
55. if (driver_register(&davinci_i2c_driver) != 0) // I2C驅動注冊
56. printk(KERN_ERR "Driver register failed for davinci_i2c\n");
57. if (platform_device_register(&davinci_i2c_device) != 0) {
58. printk(KERN_ERR "Device register failed for i2c\n");
59. driver_unregister(&davinci_i2c_driver);
60. }
62. return 0;
64. do_free_irq:
65. free_irq(IRQ_I2C, &i2c_davinci_dev);
66. do_release_region:
67. release_region(I2C_BASE, I2C_IOSIZE);
69. return status;
70. }

操作主要圍繞以下4個結構體展開：

1. static struct i2c_algorithm i2c_davinci_algo = { //主要涉及相關的I2C通信協議以及數據的傳輸和接受
2. .name = "DAVINCI I2C algorithm",
3. .id = I2C_ALGO_EXP,
4. .master_xfer = i2c_davinci_xfer,
5. .smbus_xfer = NULL,
6. .slave_send = NULL,
7. .slave_recv = NULL,
8. .algo_control = NULL,
9. .functionality = i2c_davinci_func,
10. };
12. static struct i2c_adapter i2c_davinci_adap = { //對I2C通信協議的封裝，定義的適配器實例
13. .owner = THIS_MODULE,
14. .name = "DAVINCI I2C adapter",
15. .id = I2C_ALGO_EXP,
16. .algo = &i2c_davinci_algo,
17. .algo_data = NULL,
18. .client_register = NULL,
19. .client_unregister = NULL,
20. };
22. static struct device_driver davinci_i2c_driver = { //達芬奇的設備驅動
23. .name = "davinci_i2c",
24. .bus = &platform_bus_type,
25. .remove = davinci_i2c_remove,
26. };
28. static struct platform_device davinci_i2c_device = { //定義的達芬奇平台設備
29. .name = "i2c",
30. .id = -1,
31. .dev = {
32. .driver = &davinci_i2c_driver,
33. .release = davinci_i2c_device_release,
34. },
35. };

結合以上兩段代碼，可以知道以下內容

1 .在模塊初始化函數中完成適配器與設備。的連接了設備驅動davinci_i2c_driver和平台設備davinci_i2c_device的注冊

2.獲取I2C相關端口的申請，I2C相應寄存器的物理首地址0x01C21000，完成了I2C模塊初始化操作以及IRQ_I2C=39的中斷申請。

在這裡對I2C模塊的初始化進行解析，內容如下：

1. static int i2c_davinci_reset(struct i2c_davinci_device *dev)
2. {
3. u16 psc;
4. u32 clk;
6. DEB1("i2c: reset called");
8. /* put I2C into reset */
9. dev->regs->icmdr &= ~DAVINCI_I2C_ICMDR_IRS_MASK; //首先需復位I2C模塊
11. /* NOTE: I2C Clock divider programming info
12. * As per I2C specs the following formulas provide prescalar
13. * and low/high divider values
14. *
15. * input clk --> PSC Div -----------> ICCL/H Div --> output clock
16. * module clk
17. *
18. * output clk = module clk / (PSC + 1) [ (ICCL + d) + (ICCH + d) ]
19. *
20. * Thus,
21. * (ICCL + ICCH) = clk = (input clk / ((psc +1) * output clk)) - 2d;
22. *
23. * where if PSC == 0, d = 7,
24. * if PSC == 1, d = 6
25. * if PSC > 1 , d = 5
26. */
28. psc = 26; /* To get 1MHz clock */
30. clk = ((i2c_davinci_inputClock/(psc + 1)) / (i2c_davinci_busFreq * 1000)) - 10; //i2c_davinci_busFreq=20
32. dev->regs->icpsc = psc; //PSC寄存器寫26，即預分頻數27
33. dev->regs->icclkh = (50 * clk) / 100; /* duty cycle should be 50% */
34. dev->regs->icclkl = (clk - dev->regs->icclkh); //高低電平配置內容
36. DEB1("CLK = %d", clk);
37. DEB1("PSC = %d", dev->regs->icpsc);
38. DEB1("CLKL = %d", dev->regs->icclkl);
39. DEB1("CLKH = %d", dev->regs->icclkh);
41. /* Set Own Address: */
42. dev->regs->icoar = i2c_davinci_own_addr; //oxa
44. /* Enable interrupts */
45. dev->regs->icimr = I2C_DAVINCI_INTR_ALL; //所有中斷都使能
47. /* Take the I2C module out of reset: */
48. dev->regs->icmdr |= DAVINCI_I2C_ICMDR_IRS_MASK; //使能I2C模塊
50. return 0;
51. }

主要完成Dm6441上I2C的總線時鐘的配置。以及做一些中斷使能的初始化。在這裡都是對dev->regs這個結構體指針的內容

該結構體的實際內容如下：

1. typedef struct {
2. u16 icoar;
3. u8 rsvd0[2];
4. u16 icimr;
5. u8 rsvd1[2];
6. u16 icstr;
7. u8 rsvd2[2];
8. u16 icclkl;
9. u8 rsvd3[2];
10. u16 icclkh;
11. u8 rsvd4[2];
12. u16 iccnt;
13. u8 rsvd5[2];
14. u16 icdrr;
15. u8 rsvd6[2];
16. u16 icsar;
17. u8 rsvd7[2];
18. u16 icdxr;
19. u8 rsvd8[2];
20. u16 icmdr;
21. u8 rsvd9[2];
22. u16 icivr;
23. u8 rsvd10[2];
24. u16 icemdr;
25. u8 rsvd11[2];
26. u16 icpsc;
27. u8 rsvd12[2];
28. u16 icpid1;
29. u8 rsvd13[2];
30. u16 icpid2;
31. u8 rsvd14[14];
32. u32 ipcfunc;
33. u32 icpdir;
34. u32 icpdin;
35. u32 icpdout;
36. u32 icpdset;
37. u32 icpdclr;
38. } davinci_i2cregs;
40. /**************************************************************************\
41. * Overlay structure typedef definition
42. \**************************************************************************/
43. typedef volatile davinci_i2cregs *davinci_i2cregsovly;

涉及的內容是DM6441 I2C模塊的相關寄存器。在獲取寄存器的物理首地址之後，就可以直接對這個結構體實例的內容寫數值，該結構體被包含在以下結構體中

1. struct i2c_davinci_device {
2. int cmd_complete, cmd_err;
3. wait_queue_head_t cmd_wait;
4. u8 *buf;
5. size_t buf_len;
6. davinci_i2cregsovly regs;
7. };

這裡的另一塊內容是添加適配器到I2C驅動中使用i2c_add_adapter函數完成i2c_davinci_adap（該結構體實例內容見上述代碼）

1. int i2c_add_adapter(struct i2c_adapter *adap)
2. {
3. int id, res = 0;
4. struct list_head *item;
5. struct i2c_driver *driver;
7. down(&core_lists);
9. if (idr_pre_get(&i2c_adapter_idr, GFP_KERNEL) == 0) {
10. res = -ENOMEM;
11. goto out_unlock;
12. }
14. res = idr_get_new(&i2c_adapter_idr, NULL, &id);
15. if (res < 0) {
16. if (res == -EAGAIN)
17. res = -ENOMEM;
18. goto out_unlock;
19. }
21. adap->nr = id & MAX_ID_MASK;
22. init_MUTEX(&adap->bus_lock);
23. init_MUTEX(&adap->clist_lock);
24. list_add_tail(&adap->list,&adapters);
25. INIT_LIST_HEAD(&adap->clients);
27. /* Add the adapter to the driver core.
28. * If the parent pointer is not set up,
29. * we add this adapter to the host bus.
30. */
31. if (adap->dev.parent == NULL)
32. adap->dev.parent = &platform_bus;
33. sprintf(adap->dev.bus_id, "i2c-%d", adap->nr);
34. adap->dev.driver = &i2c_adapter_driver; //適配器的設備驅動指向i2c_adapter_driver
35. adap->dev.release = &i2c_adapter_dev_release;
36. device_register(&adap->dev); //適配器設備注冊
37. device_create_file(&adap->dev, &dev_attr_name);
39. /* Add this adapter to the i2c_adapter class */
40. memset(&adap->class_dev, 0x00, sizeof(struct class_device));
41. adap->class_dev.dev = &adap->dev;
42. adap->class_dev.class = &i2c_adapter_class;
43. strlcpy(adap->class_dev.class_id, adap->dev.bus_id, BUS_ID_SIZE);
44. class_device_register(&adap->class_dev);
46. /* inform drivers of new adapters */
47. list_for_each(item,&drivers) {
48. driver = list_entry(item, struct i2c_driver, list);
49. if (driver->flags & I2C_DF_NOTIFY)
50. /* We ignore the return code; if it fails, too bad */
51. driver->attach_adapter(adap);
52. }
54. dev_dbg(&adap->dev, "registered as adapter #%d\n", adap->nr);
56. out_unlock:
57. up(&core_lists);
58. return res;
59. }

在該函數內主要完成適配器結構體中成員變量設備dev的初始化，緊接著完成適配器這個抽象設備的注冊，再完成適配器設備類的注冊以及相關設備節點的生成。