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 intspi_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 intspi_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 u32bitbang_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，linux的SPI的数据传输就到这里了。