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，linux的SPI的数据传输就到这里了。