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。
