和菜鸟一起学linux总线驱动之初识spi驱动数据传输流程

 对于SPI的一些结构体都有所了解之后呢，那么再去瞧瞧SPI的那些长见的操作的函数了。

首先看一下本人画的比较挫的数据流了，仅供参考，如有不对，不吝赐教

 

 

接下来看看各个函数吧还是：

 

SPI write

 

/**
 * spi_write - SPI synchronous write
 * @spi: device to which data will be written
 * @buf: data buffer
 * @len: data buffer size
 * Context: can sleep
 *
 * This writes the buffer and returns zero or a negative error code.
 * Callable only from contexts that can sleep.
 */
static inline int
spi_write(struct spi_device *spi, const void *buf, size_t len)
{
       struct spi_transfer   t = {
                     .tx_buf           = buf,
                     .len         = len,
              };
       struct spi_message  m;

       spi_message_init(&m);
       spi_message_add_tail(&t, &m);
       return spi_sync(spi, &m);

}

SPI发送函数，数据放在buf中，然后把要发送的数据放在工作队列中

 

SPI  read

 

/**
 * spi_read - SPI synchronous read
 * @spi: device from which data will be read
 * @buf: data buffer
 * @len: data buffer size
 * Context: can sleep
 *
 * This reads the buffer and returns zero or a negative error code.
 * Callable only from contexts that can sleep.
 */
static inline int
spi_read(struct spi_device *spi, void *buf, size_t len)
{
       struct spi_transfer   t = {
                     .rx_buf           = buf,
                     .len         = len,
              };
       struct spi_message  m;

       spi_message_init(&m);
       spi_message_add_tail(&t, &m);
       return spi_sync(spi, &m);
}

SPI接收函数，数据放在buf中，然后把要发送的数据放在工作队列中，发送出去

 

SPI write 8 bits read 8 bits

 

/* this copies txbuf and rxbuf data; for small transfers only! */
extern int spi_write_then_read(struct spi_device *spi,
              const void *txbuf, unsigned n_tx,
              void *rxbuf, unsigned n_rx);
/**
 * spi_w8r8 - SPI synchronous 8 bit write followed by 8 bit read
 * @spi: device with which data will be exchanged
 * @cmd: command to be written before data is read back
 * Context: can sleep
 *
 * This returns the (unsigned) eight bit number returned by the
 * device, or else a negative error code.  Callable only from
 * contexts that can sleep.
 */
static inline ssize_t spi_w8r8(struct spi_device *spi, u8 cmd)
{
       ssize_t                   status;
       u8                  result;
       status = spi_write_then_read(spi, &cmd, 1, &result, 1);

       /* return negative errno or unsigned value */
       return (status < 0) ? status : result;
}

 

 

SPI write 8 bit read 16 bits

 

/**
 * spi_w8r16 - SPI synchronous 8 bit write followed by 16 bit read
 * @spi: device with which data will be exchanged
 * @cmd: command to be written before data is read back
 * Context: can sleep
 *
 * This returns the (unsigned) sixteen bit number returned by the
 * device, or else a negative error code.  Callable only from
 * contexts that can sleep.
 *
 * The number is returned in wire-order, which is at least sometimes
 * big-endian.
 */
static inline ssize_t spi_w8r16(struct spi_device *spi, u8 cmd)
{
       ssize_t                   status;
       u16                result;

       status = spi_write_then_read(spi, &cmd, 1, (u8 *) &result, 2);

       /* return negative errno or unsigned value */
       return (status < 0) ? status : result;
}

 

int spi_write_then_read(struct spi_device *spi,
              const void *txbuf, unsigned n_tx,
              void *rxbuf, unsigned n_rx)
{
       static DEFINE_MUTEX(lock);

       int                 status;
       struct spi_message  message;
       struct spi_transfer   x[2];
       u8                  *local_buf;

       /* Use preallocated DMA-safe buffer.  We can't avoid copying here,
        * (as a pure convenience thing), but we can keep heap costs
        * out of the hot path ...
        */
       if ((n_tx + n_rx) > SPI_BUFSIZ)
              return -EINVAL;

       spi_message_init(&message);
       memset(x, 0, sizeof x);
       if (n_tx) {
              x[0].len = n_tx;
              spi_message_add_tail(&x[0], &message);
       }
       if (n_rx) {
              x[1].len = n_rx;
              spi_message_add_tail(&x[1], &message);
       }

       /* ... unless someone else is using the pre-allocated buffer */
       if (!mutex_trylock(&lock)) {
              local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
              if (!local_buf)
                     return -ENOMEM;
       } else
              local_buf = buf;

       memcpy(local_buf, txbuf, n_tx);
       x[0].tx_buf = local_buf;
       x[1].rx_buf = local_buf + n_tx;
       /* do the i/o */
       status = spi_sync(spi, &message);
       if (status == 0)
              memcpy(rxbuf, x[1].rx_buf, n_rx);

       if (x[0].tx_buf == buf)
              mutex_unlock(&lock);
       else
              kfree(local_buf);

       return status;
}

 

 

SPI sync

读写都会调用到spi_sync

int spi_sync(struct spi_device *spi, struct spi_message *message)
{
       return __spi_sync(spi, message, 0);
}

 

接着调用了__spi_sync

 

static int __spi_sync(struct spi_device *spi, struct spi_message *message,
                    int bus_locked)
{
       DECLARE_COMPLETION_ONSTACK(done);
       int status;
       struct spi_master *master = spi->master;

       message->complete = spi_complete;
       message->context = &done;

       if (!bus_locked)
              mutex_lock(&master->bus_lock_mutex);
        status = spi_async_locked(spi, message);

       if (!bus_locked)
              mutex_unlock(&master->bus_lock_mutex);

       if (status == 0) {
              wait_for_completion(&done);
              status = message->status;
       }
       message->context = NULL;
       return status;
}

 

 

然后就是spi_async

int spi_async(struct spi_device *spi, struct spi_message *message)
{
       struct spi_master *master = spi->master;
       int ret;
       unsigned long flags;

       spin_lock_irqsave(&master->bus_lock_spinlock, flags);

       if (master->bus_lock_flag)
              ret = -EBUSY;
       else
              ret = __spi_async(spi, message);

       spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);

       return ret;
}

 

最后调用__spi_async

static int __spi_async(struct spi_device *spi, struct spi_message *message)
{
       struct spi_master *master = spi->master;

       /* Half-duplex links include original MicroWire, and ones with
        * only one data pin like SPI_3WIRE (switches direction) or where
        * either MOSI or MISO is missing.  They can also be caused by
        * software limitations.
        */
       if ((master->flags & SPI_MASTER_HALF_DUPLEX)
                     || (spi->mode & SPI_3WIRE)) {
              struct spi_transfer *xfer;
              unsigned flags = master->flags;

              list_for_each_entry(xfer, &message->transfers, transfer_list) {
                     if (xfer->rx_buf && xfer->tx_buf)
                            return -EINVAL;
                     if ((flags & SPI_MASTER_NO_TX) && xfer->tx_buf)
                            return -EINVAL;
                     if ((flags & SPI_MASTER_NO_RX) && xfer->rx_buf)
                            return -EINVAL;
              }
       }

       message->spi = spi;
       message->status = -EINPROGRESS;
       return master->transfer(spi, message);
}

 

返回了master->transfer(spi, message);那么就是控制器里去工作了。

 

我用的是gpio模拟的spi，所以那用gpio模拟的那个控制器去看控制器的处理了。

先还是看一下probe函数

 

static int __init spi_gpio_probe(struct platform_device *pdev)

{

       int                        status;

       struct spi_master           *master;

       struct spi_gpio                     *spi_gpio;

       struct spi_gpio_platform_data       *pdata;

       u16 master_flags = 0;



       pdata = pdev->dev.platform_data;

#ifdef GENERIC_BITBANG

       if (!pdata || !pdata->num_chipselect)

              return -ENODEV;

#endif



       status = spi_gpio_request(pdata, dev_name(&pdev->dev), &master_flags);

       if (status < 0)

              return status;



       master = spi_alloc_master(&pdev->dev, sizeof *spi_gpio);

       if (!master) {

              status = -ENOMEM;

              goto gpio_free;

       }

       spi_gpio = spi_master_get_devdata(master);

       platform_set_drvdata(pdev, spi_gpio);



       spi_gpio->pdev = pdev;

       if (pdata)

              spi_gpio->pdata = *pdata;



       master->flags = master_flags;

       master->bus_num = pdev->id;

       master->num_chipselect = SPI_N_CHIPSEL;

       master->setup = spi_gpio_setup;

       master->cleanup = spi_gpio_cleanup;



       spi_gpio->bitbang.master = spi_master_get(master);

       spi_gpio->bitbang.chipselect = spi_gpio_chipselect;



       if ((master_flags & (SPI_MASTER_NO_TX | SPI_MASTER_NO_RX)) == 0) {

              spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;

              spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;

              spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;

              spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;

       } else {

              spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;

              spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;

              spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;

              spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;

       }

       spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;

       spi_gpio->bitbang.flags = SPI_CS_HIGH;



       status = spi_bitbang_start(&spi_gpio->bitbang);

       if (status < 0) {

              spi_master_put(spi_gpio->bitbang.master);

gpio_free:

              if (SPI_MISO_GPIO != SPI_GPIO_NO_MISO)

                     gpio_free(SPI_MISO_GPIO);

              if (SPI_MOSI_GPIO != SPI_GPIO_NO_MOSI)

                     gpio_free(SPI_MOSI_GPIO);

              gpio_free(SPI_SCK_GPIO);

              spi_master_put(master);

       }



       return status;

}

 

主要看下下面三个函数

spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;

spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;

status = spi_bitbang_start(&spi_gpio->bitbang);

 

spi_gpio_txrx_word_mode0;就是最后调用到的先放一边，spi_bitbang_start，看一下这个函数

 

int spi_bitbang_start(struct spi_bitbang *bitbang)

{

       int   status;



       if (!bitbang->master || !bitbang->chipselect)

              return -EINVAL;



       INIT_WORK(&bitbang->work, bitbang_work);

       spin_lock_init(&bitbang->lock);

       INIT_LIST_HEAD(&bitbang->queue);



       if (!bitbang->master->mode_bits)

              bitbang->master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;



       if (!bitbang->master->transfer)

              bitbang->master->transfer = spi_bitbang_transfer;

       if (!bitbang->txrx_bufs) {

              bitbang->use_dma = 0;

              bitbang->txrx_bufs = spi_bitbang_bufs;

              if (!bitbang->master->setup) {

                     if (!bitbang->setup_transfer)

                            bitbang->setup_transfer =

                                    spi_bitbang_setup_transfer;

                     bitbang->master->setup = spi_bitbang_setup;

                     bitbang->master->cleanup = spi_bitbang_cleanup;

              }

       } else if (!bitbang->master->setup)

              return -EINVAL;

       if (bitbang->master->transfer == spi_bitbang_transfer &&

                     !bitbang->setup_transfer)

              return -EINVAL;



       /* this task is the only thing to touch the SPI bits */

       bitbang->busy = 0;

       bitbang->workqueue = create_singlethread_workqueue(

                     dev_name(bitbang->master->dev.parent));

       if (bitbang->workqueue == NULL) {

              status = -EBUSY;

              goto err1;

       }



       /* driver may get busy before register() returns, especially

        * if someone registered boardinfo for devices

        */

       status = spi_register_master(bitbang->master);

       if (status < 0)

              goto err2;



       return status;



err2:

       destroy_workqueue(bitbang->workqueue);

err1:

       return status;

}

 

看到这个函数指针了吧：

if (!bitbang->master->transfer)

              bitbang->master->transfer = spi_bitbang_transfer;

那么设备驱动调用的master->transfer(spi, message);就是调用到了spi_bitbang_transfer了，

 

/**

 * spi_bitbang_transfer - default submit to transfer queue

 */

int spi_bitbang_transfer(struct spi_device *spi, struct spi_message *m)

{

       struct spi_bitbang   *bitbang;

       unsigned long        flags;

       int                 status = 0;



       m->actual_length = 0;

       m->status = -EINPROGRESS;



       bitbang = spi_master_get_devdata(spi->master);



       spin_lock_irqsave(&bitbang->lock, flags);

       if (!spi->max_speed_hz)

              status = -ENETDOWN;

       else {

              list_add_tail(&m->queue, &bitbang->queue);

              queue_work(bitbang->workqueue, &bitbang->work);

       }

       spin_unlock_irqrestore(&bitbang->lock, flags);



       return status;

}

这里是把信息加到了bitbang->workqueue，然后在bitbang->work里处理

 

再来看下bitbang->work做了什么

static void bitbang_work(struct work_struct *work)

{

       struct spi_bitbang   *bitbang =

              container_of(work, struct spi_bitbang, work);

       unsigned long        flags;



       spin_lock_irqsave(&bitbang->lock, flags);

       bitbang->busy = 1;

       while (!list_empty(&bitbang->queue)) {

              struct spi_message  *m;

              struct spi_device     *spi;

              unsigned         nsecs;

              struct spi_transfer   *t = NULL;

              unsigned         tmp;

              unsigned         cs_change;

              int                 status;

              int                 do_setup = -1;



              m = container_of(bitbang->queue.next, struct spi_message,

                            queue);

              list_del_init(&m->queue);

              spin_unlock_irqrestore(&bitbang->lock, flags);



              /* FIXME this is made-up ... the correct value is known to

               * word-at-a-time bitbang code, and presumably chipselect()

               * should enforce these requirements too?

               */

              nsecs = 100;



              spi = m->spi;

              tmp = 0;

              cs_change = 1;

              status = 0;



              list_for_each_entry (t, &m->transfers, transfer_list) {



                     /* override speed or wordsize? */

                     if (t->speed_hz || t->bits_per_word)

                            do_setup = 1;



                     /* init (-1) or override (1) transfer params */

                     if (do_setup != 0) {

                            status = bitbang->setup_transfer(spi, t);

                            if (status < 0)

                                   break;

                            if (do_setup == -1)

                                   do_setup = 0;

                     }



                     /* set up default clock polarity, and activate chip;

                      * this implicitly updates clock and spi modes as

                      * previously recorded for this device via setup().

                      * (and also deselects any other chip that might be

                      * selected ...)

                      */

                     if (cs_change) {

                            bitbang->chipselect(spi, BITBANG_CS_ACTIVE);

                            ndelay(nsecs);

                     }

                     cs_change = t->cs_change;

                     if (!t->tx_buf && !t->rx_buf && t->len) {

                            status = -EINVAL;

                            break;

                     }



                     /* transfer data.  the lower level code handles any

                      * new dma mappings it needs. our caller always gave

                      * us dma-safe buffers.

                      */

                     if (t->len) {

                            /* REVISIT dma API still needs a designated

                             * DMA_ADDR_INVALID; ~0 might be better.

                             */

                            if (!m->is_dma_mapped)

                                   t->rx_dma = t->tx_dma = 0;

                            status = bitbang->txrx_bufs(spi, t);

                     }

                     if (status > 0)

                            m->actual_length += status;

                     if (status != t->len) {

                            /* always report some kind of error */

                            if (status >= 0)

                                   status = -EREMOTEIO;

                            break;

                     }

                     status = 0;



                     /* protocol tweaks before next transfer */

                     if (t->delay_usecs)

                            udelay(t->delay_usecs);



                     if (!cs_change)

                            continue;

                     if (t->transfer_list.next == &m->transfers)

                            break;



                     /* sometimes a short mid-message deselect of the chip

                      * may be needed to terminate a mode or command

                      */

                     ndelay(nsecs);

                     bitbang->chipselect(spi, BITBANG_CS_INACTIVE);

                     ndelay(nsecs);

              }



              m->status = status;

              m->complete(m->context);



              /* normally deactivate chipselect ... unless no error and

               * cs_change has hinted that the next message will probably

               * be for this chip too.

               */

              if (!(status == 0 && cs_change)) {

                     ndelay(nsecs);

                     bitbang->chipselect(spi, BITBANG_CS_INACTIVE);

                     ndelay(nsecs);

              }



              spin_lock_irqsave(&bitbang->lock, flags);

       }

       bitbang->busy = 0;

       spin_unlock_irqrestore(&bitbang->lock, flags);

}

 

当队列非空的时候就一直去取队列的数据，然后会执行到

status = bitbang->setup_transfer(spi, t);

这个函数，因为在spi_bitbang_start中

if (!bitbang->txrx_bufs) {

              bitbang->use_dma = 0;

              bitbang->txrx_bufs = spi_bitbang_bufs;

              if (!bitbang->master->setup) {

                     if (!bitbang->setup_transfer)

                            bitbang->setup_transfer =

                                    spi_bitbang_setup_transfer;

                     bitbang->master->setup = spi_bitbang_setup;

                     bitbang->master->cleanup = spi_bitbang_cleanup;

              }

       }

所以就调用了spi_bitbang_setup_transfer;

 

 

int spi_bitbang_setup_transfer(struct spi_device *spi, struct spi_transfer *t)

{

       struct spi_bitbang_cs      *cs = spi->controller_state;

       u8                  bits_per_word;

       u32                hz;



       if (t) {

              bits_per_word = t->bits_per_word;

              hz = t->speed_hz;

       } else {

              bits_per_word = 0;

              hz = 0;

       }



       /* spi_transfer level calls that work per-word */

       if (!bits_per_word)

              bits_per_word = spi->bits_per_word;

       if (bits_per_word <= 8)

              cs->txrx_bufs = bitbang_txrx_8;

       else if (bits_per_word <= 16)

              cs->txrx_bufs = bitbang_txrx_16;

       else if (bits_per_word <= 32)

              cs->txrx_bufs = bitbang_txrx_32;

       else

              return -EINVAL;



       /* nsecs = (clock period)/2 */

       if (!hz)

              hz = spi->max_speed_hz;

       if (hz) {

              cs->nsecs = (1000000000/2) / hz;

              if (cs->nsecs > (MAX_UDELAY_MS * 1000 * 1000))

                     return -EINVAL;

       }



       return 0;

}

 

这里主要是根据bits_per_word选择传输的方式，分8、16,、32三种模式，ads7843touchscreen是用bits_per_word默认没有，选择bitbang_txrx_8的。

 

static unsigned bitbang_txrx_8(

       struct spi_device     *spi,

       u32                (*txrx_word)(struct spi_device *spi,

                                   unsigned nsecs,

                                   u32 word, u8 bits),

       unsigned         ns,

       struct spi_transfer   *t

) {

       unsigned         bits = t->bits_per_word ? : spi->bits_per_word;

       unsigned         count = t->len;

       const u8         *tx = t->tx_buf;

       u8                  *rx = t->rx_buf;



       while (likely(count > 0)) {

              u8           word = 0;



              if (tx)

                     word = *tx++;

              word = txrx_word(spi, ns, word, bits);

              if (rx)

                     *rx++ = word;

              count -= 1;

       }

       return t->len - count;

}

这里word = txrx_word(spi, ns, word, bits);会调用到哪里呢？，首先看下这个函数的指针指向哪里。

在spi_bitbang_start中，bitbang->master->setup = spi_bitbang_setup;

然后在spi_bitbang_setup 中有

cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];

所以，这个最终还是调用到了spi_gpio.c文件中的spi_gpio_spec_txrx_word_mode0

static u32 spi_gpio_spec_txrx_word_mode0(struct spi_device *spi,

              unsigned nsecs, u32 word, u8 bits)

{

       unsigned flags = spi->master->flags;

       return bitbang_txrx_be_cpha0(spi, nsecs, 0, flags, word, bits);

}

然后这个函数就调用了bitbang_txrx_be_cpha0，这个函数在spi-bitbang-txrx.h中

 

static inline u32

bitbang_txrx_be_cpha0(struct spi_device *spi,

              unsigned nsecs, unsigned cpol, unsigned flags,

              u32 word, u8 bits)

{

       /* if (cpol == 0) this is SPI_MODE_0; else this is SPI_MODE_2 */



       /* clock starts at inactive polarity */

       for (word <<= (32 - bits); likely(bits); bits--) {



              /* setup MSB (to slave) on trailing edge */

              if ((flags & SPI_MASTER_NO_TX) == 0)

                     setmosi(spi, word & (1 << 31));

              spidelay(nsecs);      /* T(setup) */



              setsck(spi, !cpol);

              spidelay(nsecs);



              /* sample MSB (from slave) on leading edge */

              word <<= 1;

              if ((flags & SPI_MASTER_NO_RX) == 0)

                     word |= getmiso(spi);

              setsck(spi, cpol);

       }

       return word;

}

这里就是gpio模拟的spi总线的协议过程了。这样，从最上面设备程序调用到控制器的整个数据流就结束了。

 

注：这里有一个很恶心的东东，就是在bitbang_txrx_16，bitbang_txrx_32中的

const u8         *tx = t->tx_buf;

u8                  *rx = t->rx_buf;

这里是强制转换的，由于大小端的问题，可能导致数据相反，从而传输会出现问题的，如果是8bit的，那么就没有任何问题了。

一段小插曲，也是用逻辑分析仪抓到的数据才发现的，如果没有这玩意儿，估计现在还纠结着。

OK，至此，的SPI的数据传输就到这里了。