为了加深对linux下驱动架构的理解，研究一下SPI子系统的驱动。
2.6.18内核下已经添加了完整的spi子系统了，参考mtd的分析，将从下到上层，再从上到下层的对其进行分析。
以下先从下到上的进行分析：
driver/spi下有两个底层相关的spi驱动程序：
spi_s3c24xx.c和spi_s3c24xx_gpio.c
其中spi_s3c24xx.c是基于s3c24xx下相应的spi接口的驱动程序，spi_s3c24xx_gpio.c允许用户指定3个gpio口，分别充当spi_clk、spi_mosi和spi_miso接口，模拟标准的spi总线。
s3c2410自带了两个spi接口(spi0和spi1)，在此我只研究基于s3c2410下spi接口的驱动程序spi_s3c24xx.c。
首先从spi驱动的检测函数进行分析：
static int s3c24xx_spi_probe(struct platform_device *pdev)
{
struct s3c24xx_spi *hw;
struct spi_master *master;
struct spi_board_info *bi;
struct resource *res;
int err = 0;
int i;
/* pi_alloc_master函数申请了struct spi_master+struct s3c24xx_spi大小的数据，
* spi_master_get_devdata和pi_master_get分别取出struct s3c24xx_spi和struct spi_master结构指针
*/
master = spi_alloc_master(&pdev->dev, sizeof(struct s3c24xx_spi));
if (master == NULL) {
dev_err(&pdev->dev, "No memory for spi_master\n");
err = -ENOMEM;
goto err_nomem;
}
/* 填充struct spi_master结构 */
hw = spi_master_get_devdata(master);
memset(hw, 0, sizeof(struct s3c24xx_spi));
hw->master = spi_master_get(master);
hw->pdata = pdev->dev.platform_data;
hw->dev = &pdev->dev;
if (hw->pdata == NULL) {
dev_err(&pdev->dev, "No platform data supplied\n");
err = -ENOENT;
goto err_no_pdata;
}
platform_set_drvdata(pdev, hw);//dev_set_drvdata(&pdev->dev, hw)
init_completion(&hw->done);
/* setup the state for the bitbang driver */
/* 填充hw->bitbang结构(hw->bitbang结构充当一个中间层，相当与input system的input_handle struct) */
hw->bitbang.master = hw->master;
hw->bitbang.setup_transfer = s3c24xx_spi_setupxfer;
hw->bitbang.chipselect = s3c24xx_spi_chipsel;
hw->bitbang.txrx_bufs = s3c24xx_spi_txrx;
hw->bitbang.master->setup = s3c24xx_spi_setup;
dev_dbg(hw->dev, "bitbang at %p\n", &hw->bitbang);
/* find and map our resources */
/* 申请spi所用到的资源：io、irq、时钟等 */
res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (res == NULL) {
dev_err(&pdev->dev, "Cannot get IORESOURCE_MEM\n");
err = -ENOENT;
goto err_no_iores;
}
hw->ioarea = request_mem_region(res->start, (res->end - res->start)+1,
pdev->name);
if (hw->ioarea == NULL) {
dev_err(&pdev->dev, "Cannot reserve region\n");
err = -ENXIO;
goto err_no_iores;
}
hw->regs = ioremap(res->start, (res->end - res->start)+1);
if (hw->regs == NULL) {
dev_err(&pdev->dev, "Cannot map IO\n");
err = -ENXIO;
goto err_no_iomap;
}
hw->irq = platform_get_irq(pdev, 0);
if (hw->irq < 0) {
dev_err(&pdev->dev, "No IRQ specified\n");
err = -ENOENT;
goto err_no_irq;
}
err = request_irq(hw->irq, s3c24xx_spi_irq, 0, pdev->name, hw);
if (err) {
dev_err(&pdev->dev, "Cannot claim IRQ\n");
goto err_no_irq;
}
hw->clk = clk_get(&pdev->dev, "spi");
if (IS_ERR(hw->clk)) {
dev_err(&pdev->dev, "No clock for device\n");
err = PTR_ERR(hw->clk);
goto err_no_clk;
}
/* for the moment, permanently enable the clock */
clk_enable(hw->clk);
/* program defaults into the registers */
/* 初始化spi相关的寄存器 */
writeb(0xff, hw->regs + S3C2410_SPPRE);
writeb(SPPIN_DEFAULT, hw->regs + S3C2410_SPPIN);
writeb(SPCON_DEFAULT, hw->regs + S3C2410_SPCON);
/* add by lfc */
s3c2410_gpio_setpin(S3C2410_GPE13, 0);
s3c2410_gpio_setpin(S3C2410_GPE12, 0);
s3c2410_gpio_cfgpin(S3C2410_GPE13, S3C2410_GPE13_SPICLK0);
s3c2410_gpio_cfgpin(S3C2410_GPE12, S3C2410_GPE12_SPIMOSI0);
s3c2410_gpio_cfgpin(S3C2410_GPE11, S3C2410_GPE11_SPIMISO0);
/* end add */
/* setup any gpio we can */
/* 片选 */
if (!hw->pdata->set_cs) {
s3c2410_gpio_setpin(hw->pdata->pin_cs, 1);
s3c2410_gpio_cfgpin(hw->pdata->pin_cs, S3C2410_GPIO_OUTPUT);
}
/* register our spi controller */
/* 最终通过调用spi_register_master来注册spi控制器(驱动) */
err = spi_bitbang_start(&hw->bitbang);
if (err) {
dev_err(&pdev->dev, "Failed to register SPI master\n");
goto err_register;
}
dev_dbg(hw->dev, "shutdown=%d\n", hw->bitbang.shutdown);
/* register all the devices associated */
/* 注册所用使用本spi驱动的设备 */
bi = &hw->pdata->board_info[0];
for (i = 0; i < hw->pdata->board_size; i++, bi++) {
dev_info(hw->dev, "registering %s\n", bi->modalias);
bi->controller_data = hw;
spi_new_device(master, bi);
}
return 0;
err_register:
clk_disable(hw->clk);
clk_put(hw->clk);
err_no_clk:
free_irq(hw->irq, hw);
err_no_irq:
iounmap(hw->regs);
err_no_iomap:
release_resource(hw->ioarea);
kfree(hw->ioarea);
err_no_iores:
err_no_pdata:
spi_master_put(hw->master);;
err_nomem:
return err;
}
/*
* spi_alloc_master - allocate SPI master controller
* @dev: the controller, possibly using the platform_bus
* @size: how much driver-private data to preallocate; the pointer to this
* memory is in the class_data field of the returned class_device,
* accessible with spi_master_get_devdata().
*
* This call is used only by SPI master controller drivers, which are the
* only ones directly touching chip registers. It's how they allocate
* an spi_master structure, prior to calling spi_register_master().
*
* This must be called from context that can sleep. It returns the SPI
* master structure on success, else NULL.
*
* The caller is responsible for assigning the bus number and initializing
* the master's methods before calling spi_register_master(); and (after errors
* adding the device) calling spi_master_put() to prevent a memory leak.
*/
/*注释已经写得很清楚了，本函数旨在分配spi_master struct
*其中，device为主控制设备，size为需要预分配的设备私有数据大小
*该函数被spi主控制器驱动所调用，用于在调用spi_register_master注册主控制器前
*分配spi_master struct，分配bus number和初始化主控制器的操作方法
*注意在分配spi_master struct的时候多分配了大小为size的设备私有数据
*并通过spi_master_set_devdata函数把其放到class_data field里，以后可以通过spi_master_get_devdata来访问
*/
struct spi_master * __init_or_module
spi_alloc_master(struct device *dev, unsigned size)
{
struct spi_master *master;
if (!dev)
return NULL;
master = kzalloc(size + sizeof *master, SLAB_KERNEL);
if (!master)
return NULL;
class_device_initialize(&master->cdev);
master->cdev.class = &spi_master_class;
master->cdev.dev = get_device(dev);
spi_master_set_devdata(master, &master[1]);
return master;
}
/*
* spi_bitbang_start - start up a polled/bitbanging SPI master driver
* @bitbang: driver handle
*
* Caller should have zero-initialized all parts of the structure, and then
* provided callbacks for chip selection and I/O loops. If the master has
* a transfer method, its final step should call spi_bitbang_transfer; or,
* that's the default if the transfer routine is not initialized. It should
* also set up the bus number and number of chipselects.
*
* For i/o loops, provide callbacks either per-word (for bitbanging, or for
* hardware that basically exposes a shift register) or per-spi_transfer
* (which takes better advantage of hardware like fifos or DMA engines).
*
* Drivers using per-word I/O loops should use (or call) spi_bitbang_setup and
* spi_bitbang_cleanup to handle those spi master methods. Those methods are
* the defaults if the bitbang->txrx_bufs routine isn't initialized.
*
* This routine registers the spi_master, which will process requests in a
* dedicated task, keeping IRQs unblocked most of the time. To stop
* processing those requests, call spi_bitbang_stop().
*/
int spi_bitbang_start(struct spi_bitbang *bitbang)
{
int status;
if (!bitbang->master || !bitbang->chipselect)
return -EINVAL;
/*bitbang_work
* 初始化a work，后面再create_singlethread_workqueue，
* 等到有数据要传输的时候，在spi_bitbang_transfer函数中通过调用queue_work(bitbang->workqueue, &bitbang->work)
* 把work扔进workqueue中调度运行
* 这是内核的一贯做法，在mmc/sd驱动中也是这样处理的^_^
*/
INIT_WORK(&bitbang->work, bitbang_work, bitbang);
/* 初始化自旋锁和链表头，以后用到 */
spin_lock_init(&bitbang->lock);
spi_new_device INIT_LIST_HEAD(&bitbang->queue);
if (!bitbang->master->transfer)
bitbang->master->transfer = spi_bitbang_transfer;//spi数据的传输就是通过调用这个方法来实现的
/* spi_s3c24xx.c驱动中有相应的txrx_bufs处理方法，在bitbang_work中被调用 */
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;
}
/* spi_s3c24xx.c驱动中有相应的setup处理方法，在稍后的spi_new_device中被调用 */
} else if (!bitbang->master->setup)
return -EINVAL;
/* this task is the only thing to touch the SPI bits */
bitbang->busy = 0;
/* 创建工作者进程 */
bitbang->workqueue = create_singlethread_workqueue(
bitbang->master->cdev.dev->bus_id);
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;
}
/**
* spi_register_master - register SPI master controller
* @master: initialized master, originally from spi_alloc_master()
*
* SPI master controllers connect to their drivers using some non-SPI bus,
* such as the platform bus. The final stage of probe() in that code
* includes calling spi_register_master() to hook up to this SPI bus glue.
*
* SPI controllers use board specific (often SOC specific) bus numbers,
* and board-specific addressing for SPI devices combines those numbers
* with chip select numbers. Since SPI does not directly support dynamic
* device identification, boards need configuration tables telling which
* chip is at which address.
*
* This must be called from context that can sleep. It returns zero on
* success, else a negative error code (dropping the master's refcount).
* After a successful return, the caller is responsible for calling
* spi_unregister_master().
*/
int __init_or_module
spi_register_master(struct spi_master *master)
{
static atomic_t dyn_bus_id = ATOMIC_INIT((1<<16) - 1);
struct device *dev = master->cdev.dev;
int status = -ENODEV;
int dynamic = 0;
if (!dev)
return -ENODEV;
/* convention: dynamically assigned bus IDs count down from the max */
if (master->bus_num < 0) {
master->bus_num = atomic_dec_return(&dyn_bus_id);
dynamic = 1;
}
/* register the device, then userspace will see it.
* registration fails if the bus ID is in use.
*/
snprintf(master->cdev.class_id, sizeof master->cdev.class_id,
"spi%u", master->bus_num);
status = class_device_add(&master->cdev);//注册设备
if (status < 0)
goto done;
dev_dbg(dev, "registered master %s%s\n", master->cdev.class_id,
dynamic ? " (dynamic)" : "");
/* populate children from any spi device tables */
scan_boardinfo(master);
status = 0;
done:
return status;
}
/* FIXME someone should add support for a __setup("spi", ...) that
* creates board info from kernel command lines
*/
/*
* scan board_list for spi_board_info which is registered by spi_register_board_info
* 很可惜，s3c24xx的spi驱动中不支持spi_register_board_info这种标准方式注册方式，而是直接调用spi_new_device内部函数
*/
static void __init_or_module
scan_boardinfo(struct spi_master *master)
{
struct boardinfo *bi;
struct device *dev = master->cdev.dev;
down(&board_lock);
list_for_each_entry(bi, &board_list, list) {
struct spi_board_info *chip = bi->board_info;
unsigned n;
for (n = bi->n_board_info; n > 0; n--, chip++) {
if (chip->bus_num != master->bus_num)
continue;
/* some controllers only have one chip, so they
* might not use chipselects. otherwise, the
* chipselects are numbered 0..max.
*/
if (chip->chip_select >= master->num_chipselect
&& master->num_chipselect) {
dev_dbg(dev, "cs%d > max %d\n",
chip->chip_select,
master->num_chipselect);
continue;
}
(void) spi_new_device(master, chip);
}
}
up(&board_lock);
}
/*
* Board-specific early init code calls this (probably during arch_initcall)
* with segments of the SPI device table. Any device nodes are created later,
* after the relevant parent SPI controller (bus_num) is defined. We keep
* this table of devices forever, so that reloading a controller driver will
* not make Linux forget about these hard-wired devices.
*
* Other code can also call this, e.g. a particular add-on board might provide
* SPI devices through its expansion connector, so code initializing that board
* would naturally declare its SPI devices.
*
* The board info passed can safely be __initdata ... but be careful of
* any embedded pointers (platform_data, etc), they're copied as-is.
*/
int __init
spi_register_board_info(struct spi_board_info const *info, unsigned n)
{
struct boardinfo *bi;
bi = kmalloc(sizeof(*bi) + n * sizeof *info, GFP_KERNEL);
if (!bi)
return -ENOMEM;
bi->n_board_info = n;
memcpy(bi->board_info, info, n * sizeof *info);
down(&board_lock);
list_add_tail(&bi->list, &board_list);
up(&board_lock);
return 0;
}
/* On typical mainboards, this is purely internal; and it's not needed
* after board init creates the hard-wired devices. Some development
* platforms may not be able to use spi_register_board_info though, and
* this is exported so that for example a USB or parport based adapter
* driver could add devices (which it would learn about out-of-band).
*/
struct spi_device *__init_or_module
spi_new_device(struct spi_master *master, struct spi_board_info *chip)
{
struct spi_device *proxy;//这个结构很重要，以后就是通过这个结构来操作实际的spi设备的
struct device *dev = master->cdev.dev;
int status;
/* NOTE: caller did any chip->bus_num checks necessary */
if (!spi_master_get(master))
return NULL;
proxy = kzalloc(sizeof *proxy, GFP_KERNEL);
if (!proxy) {
dev_err(dev, "can't alloc dev for cs%d\n",
chip->chip_select);
goto fail;
}
/* 初始化spi_device 结构各成员 */
proxy->master = master;
proxy->chip_select = chip->chip_select;
proxy->max_speed_hz = chip->max_speed_hz;
proxy->mode = chip->mode;
proxy->irq = chip->irq;
proxy->modalias = chip->modalias;
snprintf(proxy->dev.bus_id, sizeof proxy->dev.bus_id,
"%s.%u", master->cdev.class_id,
chip->chip_select);
proxy->dev.parent = dev;
proxy->dev.bus = &spi_bus_type;
proxy->dev.platform_data = (void *) chip->platform_data;
proxy->controller_data = chip->controller_data;
proxy->controller_state = NULL;
proxy->dev.release = spidev_release;
/* drivers may modify this default i/o setup */
/* 调用master->setup(即s3c24xx_spi_setup)函数初始化spi设备 */
status = master->setup(proxy);
if (status < 0) {
dev_dbg(dev, "can't %s %s, status %d\n",
"setup", proxy->dev.bus_id, status);
goto fail;
}
/* driver core catches callers that misbehave by defining
* devices that already exist.
*/
status = device_register(&proxy->dev);//真正注册原始设备
if (status < 0) {
dev_dbg(dev, "can't %s %s, status %d\n",
"add", proxy->dev.bus_id, status);
goto fail;
}
dev_dbg(dev, "registered child %s\n", proxy->dev.bus_id);
return proxy;
fail:
spi_master_put(master);
kfree(proxy);
return NULL;
}
static int s3c24xx_spi_setup(struct spi_device *spi)
{
int ret;
/* 进行一些检查性操作 */
if (!spi->bits_per_word)
spi->bits_per_word = 8;
if ((spi->mode & SPI_LSB_FIRST) != 0)
return -EINVAL;
ret = s3c24xx_spi_setupxfer(spi, NULL);
if (ret < 0) {
dev_err(&spi->dev, "setupxfer returned %d\n", ret);
return ret;
}
dev_dbg(&spi->dev, "%s: mode %d, %u bpw, %d hz\n",
__FUNCTION__, spi->mode, spi->bits_per_word,
spi->max_speed_hz);
return 0;
}
static int s3c24xx_spi_setupxfer(struct spi_device *spi,
struct spi_transfer *t)
{
struct s3c24xx_spi *hw = to_hw(spi);
unsigned int bpw;
unsigned int hz;
unsigned int div;
bpw = t ? t->bits_per_word : spi->bits_per_word;
hz = t ? t->speed_hz : spi->max_speed_hz;
if (bpw != 8) {
dev_err(&spi->dev, "invalid bits-per-word (%d)\n", bpw);
return -EINVAL;
}
div = clk_get_rate(hw->clk) / hz;
/* is clk = pclk / (2 * (pre+1)), or is it
* clk = (pclk * 2) / ( pre + 1) */
div = (div / 2) - 1;//求出预分频值
if (div < 0)
div = 1;
if (div > 255)
div = 255;
dev_dbg(&spi->dev, "setting pre-scaler to %d (hz %d)\n", div, hz);
writeb(div, hw->regs + S3C2410_SPPRE);//设置预分频值
spin_lock(&hw->bitbang.lock);
if (!hw->bitbang.busy) {
hw->bitbang.chipselect(spi, BITBANG_CS_INACTIVE);//修改时钟，先禁用spi
/* need to ndelay for 0.5 clocktick ? */
}
spin_unlock(&hw->bitbang.lock);
return 0;
}
static void s3c24xx_spi_chipsel(struct spi_device *spi, int value)
{
struct s3c24xx_spi *hw = to_hw(spi);
unsigned int cspol = spi->mode & SPI_CS_HIGH ? 1 : 0;
unsigned int spcon;
switch (value) {
case BITBANG_CS_INACTIVE:
/* 禁用spi(禁用片选) */
if (hw->pdata->set_cs)
hw->pdata->set_cs(hw->pdata, value, cspol);
else
s3c2410_gpio_setpin(hw->pdata->pin_cs, cspol ^ 1);
break;
case BITBANG_CS_ACTIVE:
/*
* 启用spi：根据需要设置寄存器并启用使能片选
* (如果spi_board_info中没有设置相应的mode选项的话，那就只能使用默认值SPPIN_DEFAULT和SPCON_DEFAULT了)
*/
spcon = readb(hw->regs + S3C2410_SPCON);
if (spi->mode & SPI_CPHA)
spcon |= S3C2410_SPCON_CPHA_FMTB;
else
spcon &= ~S3C2410_SPCON_CPHA_FMTB;
if (spi->mode & SPI_CPOL)
spcon |= S3C2410_SPCON_CPOL_HIGH;
else
spcon &= ~S3C2410_SPCON_CPOL_HIGH;
spcon |= S3C2410_SPCON_ENSCK;
/* write new configration */
writeb(spcon, hw->regs + S3C2410_SPCON);
if (hw->pdata->set_cs)
hw->pdata->set_cs(hw->pdata, value, cspol);
else
s3c2410_gpio_setpin(hw->pdata->pin_cs, cspol);
break;
}
}
