static struct platform_device spi_platform_dev = {
.name = "s3c24xx-spi-gpio", /* [cgw]: 设置平台设备名，和平台驱动名对应 */
.id = -1,
.dev = {
.release = spi_dev_release,
.platform_data = (void *)&spi_dev, /* [cgw]: 通过platform_data传递spi_dev给平台驱动
* 平台驱动可以访问spi_dev
*/
},
};
static int spi_dev_init(void)
{
/* [cgw]: 注册spi_platform_dev平台设备 */
platform_device_register(&spi_platform_dev);
return 0;
}
spi_bitbang.c提供了spi底层一些实现细节，注册工作队列（SPI数据的传送最终是通过调用工作队列实现的），spi工作模式，工作频率等。
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) {
/* [cgw]: spi驱动指定几位数据模式，和传送速度 */
bits_per_word = t->bits_per_word;
hz = t->speed_hz;
} else {
bits_per_word = 0;
hz = 0;
}
/* [cgw]: 根据spi位数，选择合适的时序 */
/* 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;
/* [cgw]: 设置SCLK的时钟频率 */
/* 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;
}
int spi_bitbang_setup(struct spi_device *spi)
{
struct spi_bitbang_cs *cs = spi->controller_state;
struct spi_bitbang *bitbang;
int retval;
bitbang = spi_master_get_devdata(spi->master);
/* REVISIT: some systems will want to support devices using lsb-first
* bit encodings on the wire. In pure software that would be trivial,
* just bitbang_txrx_le_cphaX() routines shifting the other way, and
* some hardware controllers also have this support.
*/
/* [cgw]: 默认不支持LSB模式，要想使用LSB模式，只要bitbang_txrx_le_cphaX()改变移位的方向即可 */
if ((spi->mode & SPI_LSB_FIRST) != 0)
return -EINVAL;
if (!cs) {
cs = kzalloc(sizeof *cs, GFP_KERNEL);
if (!cs)
return -ENOMEM;
spi->controller_state = cs;
}
/* [cgw]: 设置spi的默认位数 */
if (!spi->bits_per_word)
spi->bits_per_word = 8;
/* per-word shift register access, in hardware or bitbanging */
/* [cgw]: 设置spi的工作模式，四种 */
cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
if (!cs->txrx_word)
return -EINVAL;
/* [cgw]: 调用spi_bitbang_setup_transfer */
retval = bitbang->setup_transfer(spi, NULL);
if (retval < 0)
return retval;
dev_dbg(&spi->dev, "%s, mode %d, %u bits/w, %u nsec/bit\n",
__FUNCTION__, spi->mode & (SPI_CPOL | SPI_CPHA),
spi->bits_per_word, 2 * cs->nsecs);