linux SPI驱动——spi core（四）

一：

SPI核心，就是指/drivers/spi/目录下spi.c文件中提供给其他文件的函数，首先看下spi核心的初始化函数spi_init(void)。

1: static int __init spi_init(void) 2: { 3: int status; 4:   5: buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL); /* 初始化缓存 */ 6: if (!buf) { 7: status = -ENOMEM; 8: goto err0; 9: } 10:   11: status = bus_register(&spi_bus_type); /* 注册spi总线,此步骤之后就会在/sys/bus目录下生成spi子目录 */ 12: if (status < 0) 13: goto err1; 14:   15: status = class_register(&spi_master_class);;/* 注册spi类,此步骤之后就会在/sys/class目录下生成spi_master子目录 */ 16: if (status < 0) 17: goto err2; 18: return 0; 19:   20: err2: 21: bus_unregister(&spi_bus_type); 22: err1: 23: kfree(buf); 24: buf = NULL; 25: err0: 26: return status; 27: }

1: struct bus_type spi_bus_type = { 2: .name = "spi", 3: .dev_attrs = spi_dev_attrs, 4: .match = spi_match_device, 5: .uevent = spi_uevent, 6: .pm = &spi_pm, 7: };

1: static struct class spi_master_class = { 2: .name = "spi_master", 3: .owner = THIS_MODULE, 4: .dev_release = spi_master_release, 5: };

1: postcore_initcall(spi_init); /* 注册 */

说明：
        1) 由postcore_initcall(spi_init);可以看出，此宏在系统初始化时是先于module_init()执行的。

2) 申请的buf空间用于在spi数据传输中。

3) 接下来是总线注册和类注册。

二：

此函数是半双工的形式写then读

1: int spi_write_then_read(struct spi_device *spi,

2: const void *txbuf, unsigned n_tx,

3: void *rxbuf, unsigned n_rx)

4: {

5: static DEFINE_MUTEX(lock);

6:  

7: int status;

8: struct spi_message message;

9: struct spi_transfer x[2];

10: u8 *local_buf;

11:  

12: /* Use preallocated DMA-safe buffer. We can't avoid copying here,

13: * (as a pure convenience thing), but we can keep heap costs

14: * out of the hot path ...

15: */

16: if ((n_tx + n_rx) > SPI_BUFSIZ)

17: return -EINVAL;

18:  

19: spi_message_init(&message);

20: memset(x, 0, sizeof x);

21: if (n_tx) {

22: x[0].len = n_tx;

23: spi_message_add_tail(&x[0], &message);

24: }

25: if (n_rx) {

26: x[1].len = n_rx;

27: spi_message_add_tail(&x[1], &message);

28: }

29:  

30: /* ... unless someone else is using the pre-allocated buffer */

31: if (!mutex_trylock(&lock)) {

32: local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);

33: if (!local_buf)

34: return -ENOMEM;

35: } else

36: local_buf = buf;

37:  

38: memcpy(local_buf, txbuf, n_tx);

39: x[0].tx_buf = local_buf;

40: x[1].rx_buf = local_buf + n_tx;

41:  

42: /* do the i/o */

43: status = spi_sync(spi, &message);

44: if (status == 0)

45: memcpy(rxbuf, x[1].rx_buf, n_rx);

46:  

47: if (x[0].tx_buf == buf)

48: mutex_unlock(&lock);

49: else

50: kfree(local_buf);

51:  

52: return status;

53: }

1: 对master操作的加锁与解锁

2: int spi_bus_lock(struct spi_master *master)

3: {

4: unsigned long flags;

5:  

6: mutex_lock(&master->bus_lock_mutex);

7:  

8: spin_lock_irqsave(&master->bus_lock_spinlock, flags);

9: master->bus_lock_flag = 1;

10: spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);

11:  

12: /* mutex remains locked until spi_bus_unlock is called */

13:  

14: return 0;

15: }

16: int spi_bus_unlock(struct spi_master *master)

17: {

18: master->bus_lock_flag = 0;

19:  

20: mutex_unlock(&master->bus_lock_mutex);

21:  

22: return 0;

23: }

同步数据交互

1: int spi_sync(struct spi_device *spi, struct spi_message *message) 2: { 3: return __spi_sync(spi, message, 0); 4: } 5: int spi_sync_locked(struct spi_device *spi, struct spi_message *message) 6: { 7: return __spi_sync(spi, message, 1); 8: }

 

异步数据交互

1: int spi_async(struct spi_device *spi, struct spi_message *message) 2: { 3: struct spi_master *master = spi->master; 4: int ret; 5: unsigned long flags; 6:   7: spin_lock_irqsave(&master->bus_lock_spinlock, flags); 8:   9: if (master->bus_lock_flag) 10: ret = -EBUSY; 11: else 12: ret = __spi_async(spi, message); 13:   14: spin_unlock_irqrestore(&master->bus_lock_spinlock, flags); 15:   16: return ret; 17: } 18:   19: int spi_async_locked(struct spi_device *spi, struct spi_message *message) 20: { 21: struct spi_master *master = spi->master; 22: int ret; 23: unsigned long flags; 24:   25: spin_lock_irqsave(&master->bus_lock_spinlock, flags); 26:   27: ret = __spi_async(spi, message); 28:   29: spin_unlock_irqrestore(&master->bus_lock_spinlock, flags); 30:   31: return ret; 32:   33: }

 

//创建master

1: struct spi_master *spi_alloc_master(struct device *dev, unsigned size) 2: { 3: struct spi_master *master; 4:   5: if (!dev) 6: return NULL; 7:   8: master = kzalloc(size + sizeof *master, GFP_KERNEL); 9: if (!master) 10: return NULL; 11:   12: device_initialize(&master->dev); 13: master->dev.class = &spi_master_class; 14: master->dev.parent = get_device(dev); 15: spi_master_set_devdata(master, &master[1]); 16:   17: return master; 18: }

//spi_register_master

1: int spi_register_master(struct spi_master *master) 2: { 3: static atomic_t dyn_bus_id = ATOMIC_INIT((1<<15) - 1); 4: struct device *dev = master->dev.parent; 5: struct boardinfo *bi; 6: int status = -ENODEV; 7: int dynamic = 0; 8:   9: if (!dev) 10: return -ENODEV; 11:   12: /* even if it's just one always-selected device, there must 13: * be at least one chipselect 14: */ 15: if (master->num_chipselect == 0) 16: return -EINVAL; 17:   18: /* convention: dynamically assigned bus IDs count down from the max */ 19: if (master->bus_num < 0) { 20: /* FIXME switch to an IDR based scheme, something like 21: * I2C now uses, so we can't run out of "dynamic" IDs 22: */ 23: master->bus_num = atomic_dec_return(&dyn_bus_id); 24: dynamic = 1; 25: } 26:   27: spin_lock_init(&master->bus_lock_spinlock); 28: mutex_init(&master->bus_lock_mutex); 29: master->bus_lock_flag = 0; 30:   31: /* register the device, then userspace will see it. 32: * registration fails if the bus ID is in use. 33: */ 34: dev_set_name(&master->dev, "spi%u", master->bus_num); 35: status = device_add(&master->dev); 36: if (status < 0) 37: goto done; 38: dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev), 39: dynamic ? " (dynamic)" : ""); 40:   41: mutex_lock(&board_lock); 42: list_add_tail(&master->list, &spi_master_list); 43: list_for_each_entry(bi, &board_list, list) 44: spi_match_master_to_boardinfo(master, &bi->board_info); 45: mutex_unlock(&board_lock); 46:   47: status = 0; 48:   49: /* Register devices from the device tree */ 50: of_register_spi_devices(master); 51: done: 52: return status; 53: }

分析以上spi_register_master代码：

1.  spi_match_master_to_boardinfo会将master和每个注册进来的device board联系起来