Linux SD卡驱动开发(二) —— SD 卡驱动分析HOST篇
回顾一下前面的知识，MMC 子系统范围三个部分：
HOST 部分是针对不同主机的驱动程序，这一部是驱动程序工程师需要根据自己的特点平台来完成的。
CORE 部分: 这是整个MMC 的核心存，这部分完成了不同协议和规范的实现，并为HOST 层的驱动提供了接口函数。
CARD 部分：因为这些记忆卡都是块设备，当然需要提供块设备的驱动程序，这部分就是实现了将你的SD 卡如何实现为块设备的。
它们分布于下面的文件夹中 Linux/drivers/mmc中
其中，card（区块层） 与core（核心层）是linux系统封装好了部分，我们不需要修改，host（主控制器层）中提供与各芯片构架相关的文件，这才是我们所要开发的部分
核心层根据需要构造各种MMC/SD命令，这些命令怎么发送给MMC/SD卡呢？这通过主机控制器层来实现。这层是架构相关的，里面针对各款CPU提供一个文件，目前支持的CPU还很少。
以本节即将移植的s3cmci.c为例，它首先进行一些低层设置，比如设置MMC/SD/SDIO控制器使用到的CPIO引脚、使能控制器、注册中断处理函数等，然后向上面的核心层增加一个主机（Host），这样核心层就能调用s3cmci.c提供的函数来识别、使用具体存储卡了。
在向核心层增加主机之前，s3cmci.c 设置了一个mmc_host_ops结构体，它实现两个函数：
a -- 发起访问请求的request函数
b -- 进行一些属性设置（时钟频率、数据线位宽等）的set_ios函数。
下面列出识别存储卡、区块层发起操作请求两种情况下函数的主要调用关系：
1）识别存储卡
2）区块层发起操作请求
以后上次对存储卡的操作都通过调用这两个函数来完成。下面对HOST层进行分析（Linux内核版本:Linux-3.14）。
一、struct mmc_host 结构体
主要用来描述卡控制器位， 结构体mmc_host定义于/include/linux/mmc/host.c，可以认为是linux为SD卡控制器专门准备的一个类，该类里面的成员是所有SD卡控制器都需要的，放之四海而皆准的数据结构，在本例芯片控制器的驱动程序s3cmci.c中，则为该类具体化了一个对象struct mmc_host *mmc，此mmc指针即指代着该ARM芯片SD卡控制器的一个具体化对象（可以看出虽然C是面向过程的语言，但还是用到了一些面向对象思想的）。
在linux/driver/mmc/host/s3cmci.h下定义
struct s3cmci_host {
struct platform_device *pdev;
struct s3c24xx_mci_pdata *pdata;
struct mmc_host *mmc;
struct resource *mem;
struct clk *clk;
void __iomem *base;
int irq;
int irq_cd;
int dma;
unsigned long clk_rate;
unsigned long clk_div;
unsigned long real_rate;
u8 prescaler;
int is2440;
unsigned sdiimsk;
unsigned sdidata;
int dodma;
int dmatogo;
bool irq_disabled;
bool irq_enabled;
bool irq_state;
int sdio_irqen;
struct mmc_request *mrq;
int cmd_is_stop;
spinlock_t complete_lock;
enum s3cmci_waitfor complete_what;
int dma_complete;
u32 pio_sgptr;
u32 pio_bytes;
u32 pio_count;
u32 *pio_ptr;
#define XFER_NONE 0
#define XFER_READ 1
#define XFER_WRITE 2
u32 pio_active;
int bus_width;
char dbgmsg_cmd[301];
char dbgmsg_dat[301];
char *status;
unsigned int ccnt, dcnt;
struct tasklet_struct pio_tasklet;
#ifdef CONFIG_DEBUG_FS
struct dentry *debug_root;
struct dentry *debug_state;
struct dentry *debug_regs;
#endif
#ifdef CONFIG_CPU_FREQ
struct notifier_block freq_transition;
#endif
};其中struct mmc_host（linux/include/linux/mmc/host.h)用于与core层的命令请求，数据 传输等信息,这里代码较长，展示部分
struct mmc_host
{
const struct mmc_host_ops *ops; // SD卡主控制器的操作函数，即该控制器所具备的驱动能力
const struct mmc_bus_ops *bus_ops; // SD总线驱动的操作函数，即SD总线所具备的驱动能力
struct mmc_ios ios; // 配置时钟、总线、电源、片选、时序等
struct mmc_card *card; // 连接到此主控制器的SD卡设备
... ...
};
本文中struct mmc_host_ops *ops定义
static struct mmc_host_ops s3cmci_ops = {
.request = s3cmci_request,
.set_ios = s3cmci_set_ios,
.get_ro = s3cmci_get_ro,
.get_cd = s3cmci_card_present,
.enable_sdio_irq = s3cmci_enable_sdio_irq,
};二、SD控制器之初始化（linux/driver/mmc/host）
这一层讲述硬件与硬件之间将要发生的故事，也是最底层驱动的核心。通常所谓的驱动程序设计的任务将落实到这一层上，所以关注host故事的发展也将成为移植整个SD类设备驱动的核心。在host 目录中有各种平台下SD 卡主机驱动器的实例，这里我们选择s3c2440平台作为分析的重点。参看Kconfig和Makefile即可获得相应信息，这里对应的文件即是s3cmci.c。
1、设备的注册
旧瓶装新酒，还是那个module_init，不一样的是其中的入口函数。在s3cmci.c中对应的是module_init(s3cmci_init);
module_platform_driver(s3cmci_driver);这里是不是很奇怪，不应该是module_init 与 module_exit 吗？module_platform_driver其实是一个宏定义，定义在include/linux/platform_device.h文件中：
/* module_platform_driver() - Helper macro for drivers that don't do
* anything special in module init/exit. This eliminates a lot of
* boilerplate. Each module may only use this macro once, and
* calling it replaces module_init() and module_exit()
*/
#define module_platform_driver(__platform_driver) \
module_driver(__platform_driver, platform_driver_register, \
platform_driver_unregister)宏module_driver定义在include/linux/device.h文件中，其内容如下：
/**
* module_driver() - Helper macro for drivers that don't do anything
* special in module init/exit. This eliminates a lot of boilerplate.
* Each module may only use this macro once, and calling it replaces
* module_init() and module_exit().
*
* @__driver: driver name
* @__register: register function for this driver type
* @__unregister: unregister function for this driver type
* @...: Additional arguments to be passed to __register and __unregister.
*
* Use this macro to construct bus specific macros for registering
* drivers, and do not use it on its own.
*/
#define module_driver(__driver, __register, __unregister, ...) \
static int __init __driver##_init(void) \
{ \
return __register(&(__driver) , ##__VA_ARGS__); \
} \
module_init(__driver##_init); \
static void __exit __driver##_exit(void) \
{ \
__unregister(&(__driver) , ##__VA_ARGS__); \
} \
module_exit(__driver##_exit);2、probe函数
在驱动的接口函数中s3cmci_probe() 函数，用于分配mmc_host ，s3cmci_host结构体，并对结构体进行设置，在SDI主机控制器操作接口函数mmc_host_ops中会调用s3cmci_host结构体，申请中断并设置中断服务函数，将结构体mmc_host添加到主机。
SD主控制器驱动程序的初始化函数probe(struct platform_device *pdev)，概括地讲，主要完成五大任务，
-
初始化设备的数据结构，并将数据挂载到pdev->dev.driver_data下
-
实现设备驱动的功能函数，如mmc->ops = &s3cmci_ops;
-
申请中断函数request_irq()
- 注册设备，即注册kobject，建立sys文件，发送uevent等
-
其他需求，如在/proc/driver下建立用户交互文件等
首先还是来大致看一下s3cmci_driver中所对应的具体内容
static struct platform_driver s3cmci_driver = {
.driver = {
.name = "s3c-sdi",
.owner = THIS_MODULE,
},
.id_table = s3cmci_driver_ids,
.probe = s3cmci_probe,
.remove = s3cmci_remove,
.shutdown = s3cmci_shutdown,
};先看这几行
static int s3cmci_probe(struct platform_device *pdev)
{
struct s3cmci_host *host;
struct mmc_host *mmc;
int ret;
int is2440;
int i;
is2440 = platform_get_device_id(pdev)->driver_data;
mmc = mmc_alloc_host(sizeof(struct s3cmci_host), &pdev->dev);
if (!mmc) {
ret = -ENOMEM;
goto probe_out;
}这里，mmc = mmc_alloc_host(sizeof(struct s3cmci_host), &pdev->dev); 分配一个mmc的控制器，同时struct s3cmci_host 结构作为一个私有数据类型将添加到struct mmc_host的private域。
a -- mmc_alloc_host
mmc_alloc_host相应的代码如下：linux/drivers/mmc/core/host.c
struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
{
int err;
struct mmc_host *host;
host = kzalloc(sizeof(struct mmc_host) + extra, GFP_KERNEL);
if (!host)
return NULL;
/* scanning will be enabled when we're ready */
host->rescan_disable = 1;
idr_preload(GFP_KERNEL);
spin_lock(&mmc_host_lock);
err = idr_alloc(&mmc_host_idr, host, 0, 0, GFP_NOWAIT);
if (err >= 0)
host->index = err;
spin_unlock(&mmc_host_lock);
idr_preload_end();
if (err < 0)
goto free;
dev_set_name(&host->class_dev, "mmc%d", host->index);
host->parent = dev;
host->class_dev.parent = dev;
host->class_dev.class = &mmc_host_class;
device_initialize(&host->class_dev);
mmc_host_clk_init(host);
mutex_init(&host->slot.lock);
host->slot.cd_irq = -EINVAL;
spin_lock_init(&host->lock);
init_waitqueue_head(&host->wq);
INIT_DELAYED_WORK(&host->detect, mmc_rescan);
#ifdef CONFIG_PM
host->pm_notify.notifier_call = mmc_pm_notify;
#endif
/*
* By default, hosts do not support SGIO or large requests.
* They have to set these according to their abilities.
*/
host->max_segs = 1;
host->max_seg_size = PAGE_CACHE_SIZE;
host->max_req_size = PAGE_CACHE_SIZE;
host->max_blk_size = 512;
host->max_blk_count = PAGE_CACHE_SIZE / 512;
return host;
free:
kfree(host);
return NULL;
}24-27行主要是初始化host->class_dev，这个日后会通过device_register注册进系统。
35行前面已经在这个等待队列上花了不少笔墨，主要是同步对host资源的竞争的。
45-50行这些个都是设置host的一些属性的，是与block.c中请求队列的设置相对应的。
重新回到s3cmci_probe....
for (i = S3C2410_GPE(5); i <= S3C2410_GPE(10); i++) {
ret = gpio_request(i, dev_name(&pdev->dev));
if (ret) {
dev_err(&pdev->dev, "failed to get gpio %d\n", i);
for (i--; i >= S3C2410_GPE(5); i--)
gpio_free(i);
goto probe_free_host;
}
}上面这一段申请SD卡驱动器所需的GPIO资源。
继续分析...
host = mmc_priv(mmc);
host->mmc = mmc;
host->pdev = pdev;
host->is2440 = is2440; host->pdata = pdev->dev.platform_data;
if (!host->pdata) {
pdev->dev.platform_data = &s3cmci_def_pdata;
host->pdata = &s3cmci_def_pdata;
}这是平台设备注册时platform_device所具有的属性.
spin_lock_init(&host->complete_lock);
tasklet_init(&host->pio_tasklet, pio_tasklet, (unsigned long) host);tasklet就象一个内核定时器, 在一个"软中断"的上下文中执行(以原子模式),常用在硬件中断处理中，使得可以使得复杂的任务安全地延后到以后的时间处理。task_init 建立一个tasklet，然后调用函数 tasklet_schedule将这个tasklet放在 tasklet_vec链表的头部，并唤醒后台线程 ksoftirqd。当后台线程ksoftirqd 运行调用__do_softirq 时，会执行在中断向量表softirq_vec里中断号TASKLET_SOFTIRQ对应的 tasklet_action函数，然后 tasklet_action遍历 tasklet_vec链表，调用每个 tasklet的函数完成软中断操作，上面例子中即是pio_tasklet函数，另外软中断处理函数只能传递一个long型变量。这里是直接使用host的地址，作为传递参数。关于这个pio_tasklet现在说他还为时过早，等时辰一到自然会对他大书特书。
if (is2440) {
host->sdiimsk = S3C2440_SDIIMSK;
host->sdidata = S3C2440_SDIDATA;
host->clk_div = 1;
} else {
host->sdiimsk = S3C2410_SDIIMSK;
host->sdidata = S3C2410_SDIDATA;
host->clk_div = 2;
}host->sdiimsk 、host->sdidata分别用来存放host控制器SDI中断屏蔽寄存器和SDI数据寄存器相对SDI 寄存器的偏移地址。对于s3c2440 根据芯片手册SDIIntMsk 偏移地址为0x3C，SDIDAT偏移地址为0x40。最后host->clk_div就是指的SDI使用的时钟分频系数了。
host->complete_what = COMPLETION_NONE;
host->pio_active = XFER_NONE;host->complete_what 是一个枚举类型变量，实际上用以标示传输完成的状态；host->pio_active标示数据传输的方向，所以在这里一起初始化为空。关于传输完成的标示为了后面分析方便还是一起列举出来：
enum s3cmci_waitfor {
COMPLETION_NONE,
COMPLETION_FINALIZE,
COMPLETION_CMDSENT,
COMPLETION_RSPFIN,
COMPLETION_XFERFINISH,
COMPLETION_XFERFINISH_RSPFIN,
};继续分析
#ifdef CONFIG_MMC_S3C_PIODMA
host->dodma = host->pdata->use_dma;
#endif host->mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
if (!host->mem) {
dev_err(&pdev->dev,
"failed to get io memory region resource.\n");
ret = -ENOENT;
goto probe_free_gpio;
}
host->mem = request_mem_region(host->mem->start,
resource_size(host->mem), pdev->name);
if (!host->mem) {
dev_err(&pdev->dev, "failed to request io memory region.\n");
ret = -ENOENT;
goto probe_free_gpio;
}
host->base = ioremap(host->mem->start, resource_size(host->mem));
if (!host->base) {
dev_err(&pdev->dev, "failed to ioremap() io memory region.\n");
ret = -EINVAL;
goto probe_free_mem_region;
} 这段代码会申请这个资源并检查是否可用，当然只要之前没有使用过SDI寄存器空间，这里都会申请成功。最后就是IO映射，将实地址映射为内核虚拟地址使用。最后，host->base将保持SDI寄存器基地址所对应的内核虚拟地址。
host->irq = platform_get_irq(pdev, 0);
if (host->irq == 0) {
dev_err(&pdev->dev, "failed to get interrupt resource.\n");
ret = -EINVAL;
goto probe_iounmap;
}
if (request_irq(host->irq, s3cmci_irq, 0, DRIVER_NAME, host)) {
dev_err(&pdev->dev, "failed to request mci interrupt.\n");
ret = -ENOENT;
goto probe_iounmap;
}上面一段是对中断资源的申请，并通过request_irq安装了中断处理函数，使能了SDI中断。在上段最为关心的是s3cmci_irq 中断处理函数及其传入的dev_id。关于这个处理函数的分析后面讲述数据传输的时候会进行细致分析。接着向下....
/* We get spurious interrupts even when we have set the IMSK
* register to ignore everything, so use disable_irq() to make
* ensure we don't lock the system with un-serviceable requests. */
disable_irq(host->irq);
host->irq_state = false;if (!host->pdata->no_detect) {
ret = gpio_request(host->pdata->gpio_detect, "s3cmci detect");
if (ret) {
dev_err(&pdev->dev, "failed to get detect gpio\n");
goto probe_free_irq;
}如果SD卡存在的检查一般是通过读取专用引脚状态来实现的，这里如果需要做detect相关的工作的话就必须重新分配一个管脚，在当前系统中前面定义了以GPG8作为检测引脚
host->irq_cd = gpio_to_irq(host->pdata->gpio_detect);s3c2410_gpio_getirq是获取这个GPIO的外部中断向量号，可见后面的SD卡的检测可能会用到这个引脚的外部中断。
if (host->irq_cd >= 0) {
if (request_irq(host->irq_cd, s3cmci_irq_cd,
IRQF_TRIGGER_RISING |
IRQF_TRIGGER_FALLING,
DRIVER_NAME, host)) {
dev_err(&pdev->dev,
"can't get card detect irq.\n");
ret = -ENOENT;
goto probe_free_gpio_cd;
}
} else {
dev_warn(&pdev->dev,
"host detect has no irq available\n");
gpio_direction_input(host->pdata->gpio_detect);
}
} else
host->irq_cd = -1;上面的这段代码意图很明显就是要申请这个中断了，s3cmci_irq_cd是其处理函数。对像SD卡这种可移出设备来作为块设备存储介质的话，大多会涉及到媒体切换，具体这方面的内容后面用到的时候也会有个详细分析。
if (!host->pdata->no_wprotect) {
ret = gpio_request(host->pdata->gpio_wprotect, "s3cmci wp");
if (ret) {
dev_err(&pdev->dev, "failed to get writeprotect\n");
goto probe_free_irq_cd;
}
gpio_direction_input(host->pdata->gpio_wprotect);
}
/* depending on the dma state, get a dma channel to use. */
if (s3cmci_host_usedma(host)) {
host->dma = s3c2410_dma_request(DMACH_SDI, &s3cmci_dma_client,
host);
if (host->dma < 0) {
dev_err(&pdev->dev, "cannot get DMA channel.\n");
if (!s3cmci_host_canpio()) {
ret = -EBUSY;
goto probe_free_gpio_wp;
} else {
dev_warn(&pdev->dev, "falling back to PIO.\n");
host->dodma = 0;
}
}
}1行这个我们之前就默认为TURE了，所以接下来的几行代码是免不了。
14 行s3c2410_dma_request 申请DMA 通道，对s3c2440 平台有4 通道的DMA。而DMACH_SDI 是一个虚拟的通道号，由于这部分代码是和硬件紧密相关的，而且整个DMA的管理相对来讲比较复杂，所以这里只是粗略了解一下。
host->clk = clk_get(&pdev->dev, "sdi");
if (IS_ERR(host->clk)) {
dev_err(&pdev->dev, "failed to find clock source.\n");
ret = PTR_ERR(host->clk);
host->clk = NULL;
goto probe_free_dma;
}
ret = clk_enable(host->clk);
if (ret) {
dev_err(&pdev->dev, "failed to enable clock source.\n");
goto clk_free;
}
host->clk_rate = clk_get_rate(host->clk);以上是关于sdi时钟和波特率的有关设置，都是内核提供的一些简单的函数调用，相关的内容不是现在研究的重点就不再详细分析了。
mmc->ops = &s3cmci_ops;
mmc->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;
#ifdef CONFIG_MMC_S3C_HW_SDIO_IRQ
mmc->caps = MMC_CAP_4_BIT_DATA | MMC_CAP_SDIO_IRQ;
#else
mmc->caps = MMC_CAP_4_BIT_DATA;
#endif
mmc->f_min = host->clk_rate / (host->clk_div * 256);
mmc->f_max = host->clk_rate / host->clk_div;
if (host->pdata->ocr_avail)
mmc->ocr_avail = host->pdata->ocr_avail;
mmc->max_blk_count = 4095;
mmc->max_blk_size = 4095;
mmc->max_req_size = 4095 * 512;
mmc->max_seg_size = mmc->max_req_size;
mmc->max_segs = 128;
dbg(host, dbg_debug,
"probe: mode:%s mapped mci_base:%p irq:%u irq_cd:%u dma:%u.\n",
(host->is2440?"2440":""),
host->base, host->irq, host->irq_cd, host->dma);
上面就是对这个将要出嫁的mmc_host进行最后的设置，mmc->ops = &s3cmci_ops; 就是一直以来向core层提供的接口函数集。后面的分析可能部分是围绕它其中的函数展开的。
ret = s3cmci_cpufreq_register(host);
if (ret) {
dev_err(&pdev->dev, "failed to register cpufreq\n");
goto free_dmabuf;
}这里使用的是Linux的通告机制，s3cmci_cpufreq_register相对应的代码如下：
static inline int s3cmci_cpufreq_register(struct s3cmci_host *host) {
host->freq_transition.notifier_call = s3cmci_cpufreq_transition;
return cpufreq_register_notifier(&host->freq_transition,
CPUFREQ_TRANSITION_NOTIFIER);
}
cpufreq_register_notifier cpu是将host->freq_transition注册到CPU频率通告链上，这个是由内核维护的，当cpu频率改变时将会调用上面注册的s3cmci_cpufreq_transition的内容。
ret = mmc_add_host(mmc);
if (ret) {
dev_err(&pdev->dev, "failed to add mmc host.\n");
goto free_cpufreq;
}b -- mmc_add_host
这是core层的函数，他保存了所有平台通用的代码。同时看上去简简单单的一个mmc_add_host，可能蕴藏着天大的玄机。为此我们将为mmc_add_host另分一章，作为core层的续集，专门讲述mmc_add_host过程中发生的点点滴滴....在开始分析mmc_add_host之前，让我们还是结束SD主机控制器的probe函数，接下来
s3cmci_debugfs_attach(host);
platform_set_drvdata(pdev, mmc);
dev_info(&pdev->dev, "%s - using %s, %s SDIO IRQ\n", mmc_hostname(mmc),
s3cmci_host_usedma(host) ? "dma" : "pio",
mmc->caps & MMC_CAP_SDIO_IRQ ? "hw" : "sw");
return 0;
free_cpufreq:
s3cmci_cpufreq_deregister(host);
free_dmabuf:
clk_disable(host->clk);
clk_free:
clk_put(host->clk);
probe_free_dma:
if (s3cmci_host_usedma(host))
s3c2410_dma_free(host->dma, &s3cmci_dma_client);
probe_free_gpio_wp:
if (!host->pdata->no_wprotect)
gpio_free(host->pdata->gpio_wprotect);
probe_free_gpio_cd:
if (!host->pdata->no_detect)
gpio_free(host->pdata->gpio_detect);
probe_free_irq_cd:
if (host->irq_cd >= 0)
free_irq(host->irq_cd, host);
probe_free_irq:
free_irq(host->irq, host);
probe_iounmap:
iounmap(host->base);
probe_free_mem_region:
release_mem_region(host->mem->start, resource_size(host->mem));
probe_free_gpio:
for (i = S3C2410_GPE(5); i <= S3C2410_GPE(10); i++)
gpio_free(i);
probe_free_host:
mmc_free_host(mmc);
probe_out:
return ret;
}
static void s3cmci_shutdown(struct platform_device *pdev)
{
struct mmc_host *mmc = platform_get_drvdata(pdev);
struct s3cmci_host *host = mmc_priv(mmc);
if (host->irq_cd >= 0)
free_irq(host->irq_cd, host);
s3cmci_debugfs_remove(host);
s3cmci_cpufreq_deregister(host);
mmc_remove_host(mmc);
clk_disable(host->clk);
}上面的基本都是出错的处理了，那么也就没有必要纠结于此了，赶快开启新的生活吧....
再多说一句，可以看到probe函数里面，大量的工作是对 host 结构体 mmc结构体的填充，类似于USB probe函数中对 usb_skel 结构体的填充，向上提供接口函数。
三、 设备驱动的功能函数
一般情况下，设备驱动里都有一个行为函数结构体，比如字符设备驱动里的struct file_operations *fops，该结构描述了设备所具备的工作能力，比如open, read, write等，
struct file_operations {
struct module *owner;
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
int (*open) (struct inode *, struct file *);
... ...
};
同理，SD主控制器驱动程序里也有一个类似的结构struct mmc_host_ops *ops，它描述了该控制器所具备驱动的能力。
static struct mmc_host_ops s3cmci_ops = {
.request = s3cmci_request,
.set_ios = s3cmci_set_ios,
.get_ro = s3cmci_get_ro,
.get_cd = s3cmci_card_present,
.enable_sdio_irq = s3cmci_enable_sdio_irq,
};static void s3cmci_request(struct mmc_host *mmc, struct mmc_request *mrq)
{
struct s3cmci_host *host = mmc_priv(mmc);
host->status = "mmc request";
host->cmd_is_stop = 0;
host->mrq = mrq;
if (s3cmci_card_present(mmc) == 0) {
dbg(host, dbg_err, "%s: no medium present\n", __func__);
host->mrq->cmd->error = -ENOMEDIUM;
mmc_request_done(mmc, mrq);
} else
s3cmci_send_request(mmc);
}可以看到这里调用了s3cmci_send_request(mmc) 函数，定义如下：
static void s3cmci_send_request(struct mmc_host *mmc)
{
struct s3cmci_host *host = mmc_priv(mmc);
struct mmc_request *mrq = host->mrq;
struct mmc_command *cmd = host->cmd_is_stop ? mrq->stop : mrq->cmd;
host->ccnt++;
prepare_dbgmsg(host, cmd, host->cmd_is_stop);
/* Clear command, data and fifo status registers
Fifo clear only necessary on 2440, but doesn't hurt on 2410
*/
writel(0xFFFFFFFF, host->base + S3C2410_SDICMDSTAT);
writel(0xFFFFFFFF, host->base + S3C2410_SDIDSTA);
writel(0xFFFFFFFF, host->base + S3C2410_SDIFSTA);
if (cmd->data) {
int res = s3cmci_setup_data(host, cmd->data);
host->dcnt++;
if (res) {
dbg(host, dbg_err, "setup data error %d\n", res);
cmd->error = res;
cmd->data->error = res;
mmc_request_done(mmc, mrq);
return;
}
if (s3cmci_host_usedma(host))
res = s3cmci_prepare_dma(host, cmd->data);
else
res = s3cmci_prepare_pio(host, cmd->data);
if (res) {
dbg(host, dbg_err, "data prepare error %d\n", res);
cmd->error = res;
cmd->data->error = res;
mmc_request_done(mmc, mrq);
return;
}
}
/* Send command */
s3cmci_send_command(host, cmd);
/* Enable Interrupt */
s3cmci_enable_irq(host, true);
}其中有两个重要的结构体 s3cmci_setup_data(host, cmd->data)实现数据传输 及s3cmci_send_command(host, cmd)实现指令传输，至此，我们需要接触SD主控制器的芯片手册了。
首先，SD主控制器由一系列32位寄存器组成。通过软件的方式，即对寄存器赋值，来控制SD主控制器，进而扮演SD主控制器的角色与SD卡取得通信。
1) cmdat
根据主控制器的芯片手册，寄存器MMC_CMDAT控制命令和数据的传输，具体内容如下
结合对寄存器MMC_CMDAT的描述，分析代码
host->cmdat &= ~CMDAT_INIT; // 非初始化状态
if (mrq->data) { // 如果存在数据需要传输
pxamci_setup_data(host, mrq->data); // 实现主控制器与SD卡之间数据的传输
cmdat &= ~CMDAT_BUSY; // 没有忙碌busy信号
cmdat |= CMDAT_DATAEN | CMDAT_DMAEN; // 有数据传输，使用DMA
if (mrq->data->flags & MMC_DATA_WRITE)
cmdat |= CMDAT_WRITE; // 设置为写数据
if (mrq->data->flags & MMC_DATA_STREAM)
cmdat |= CMDAT_STREAM; // 设置为数据流stream模式
}通过DMA实现主控制器与SD卡之间数据的传输
static int s3cmci_setup_data(struct s3cmci_host *host, struct mmc_data *data)
{
u32 dcon, imsk, stoptries = 3;
/* write DCON register */
if (!data) {
writel(0, host->base + S3C2410_SDIDCON);
return 0;
}
if ((data->blksz & 3) != 0) {
/* We cannot deal with unaligned blocks with more than
* one block being transferred. */
if (data->blocks > 1) {
pr_warning("%s: can't do non-word sized block transfers (blksz %d)\n", __func__, data->blksz);
return -EINVAL;
}
}
while (readl(host->base + S3C2410_SDIDSTA) &
(S3C2410_SDIDSTA_TXDATAON | S3C2410_SDIDSTA_RXDATAON)) {
dbg(host, dbg_err,
"mci_setup_data() transfer stillin progress.\n");
writel(S3C2410_SDIDCON_STOP, host->base + S3C2410_SDIDCON);
s3cmci_reset(host);
if ((stoptries--) == 0) {
dbg_dumpregs(host, "DRF");
return -EINVAL;
}
}
dcon = data->blocks & S3C2410_SDIDCON_BLKNUM_MASK;
if (s3cmci_host_usedma(host))
dcon |= S3C2410_SDIDCON_DMAEN;
if (host->bus_width == MMC_BUS_WIDTH_4)
dcon |= S3C2410_SDIDCON_WIDEBUS;
if (!(data->flags & MMC_DATA_STREAM))
dcon |= S3C2410_SDIDCON_BLOCKMODE;
if (data->flags & MMC_DATA_WRITE) {
dcon |= S3C2410_SDIDCON_TXAFTERRESP;
dcon |= S3C2410_SDIDCON_XFER_TXSTART;
}
if (data->flags & MMC_DATA_READ) {
dcon |= S3C2410_SDIDCON_RXAFTERCMD;
dcon |= S3C2410_SDIDCON_XFER_RXSTART;
}
if (host->is2440) {
dcon |= S3C2440_SDIDCON_DS_WORD;
dcon |= S3C2440_SDIDCON_DATSTART;
}
writel(dcon, host->base + S3C2410_SDIDCON);
/* write BSIZE register */
writel(data->blksz, host->base + S3C2410_SDIBSIZE);
/* add to IMASK register */
imsk = S3C2410_SDIIMSK_FIFOFAIL | S3C2410_SDIIMSK_DATACRC |
S3C2410_SDIIMSK_DATATIMEOUT | S3C2410_SDIIMSK_DATAFINISH;
enable_imask(host, imsk);
/* write TIMER register */
if (host->is2440) {
writel(0x007FFFFF, host->base + S3C2410_SDITIMER);
} else {
writel(0x0000FFFF, host->base + S3C2410_SDITIMER);
/* FIX: set slow clock to prevent timeouts on read */
if (data->flags & MMC_DATA_READ)
writel(0xFF, host->base + S3C2410_SDIPRE);
}
return 0;
}3) m3cmci_start_cmd
实现主控制器与SD卡之间指令的传输
static void s3cmci_send_command(struct s3cmci_host *host,
struct mmc_command *cmd)
{
u32 ccon, imsk;
imsk = S3C2410_SDIIMSK_CRCSTATUS | S3C2410_SDIIMSK_CMDTIMEOUT |
S3C2410_SDIIMSK_RESPONSEND | S3C2410_SDIIMSK_CMDSENT |
S3C2410_SDIIMSK_RESPONSECRC;
enable_imask(host, imsk);
if (cmd->data)
host->complete_what = COMPLETION_XFERFINISH_RSPFIN;
else if (cmd->flags & MMC_RSP_PRESENT)
host->complete_what = COMPLETION_RSPFIN;
else
host->complete_what = COMPLETION_CMDSENT;
writel(cmd->arg, host->base + S3C2410_SDICMDARG);
ccon = cmd->opcode & S3C2410_SDICMDCON_INDEX;
ccon |= S3C2410_SDICMDCON_SENDERHOST | S3C2410_SDICMDCON_CMDSTART;
if (cmd->flags & MMC_RSP_PRESENT)
ccon |= S3C2410_SDICMDCON_WAITRSP;
if (cmd->flags & MMC_RSP_136)
ccon |= S3C2410_SDICMDCON_LONGRSP;
writel(ccon, host->base + S3C2410_SDICMDCON);
}> response类型
根据SD卡的协议，当SD卡收到从控制器发来的cmd指令后，SD卡会发出response相应，而response的类型分为R1,R1b,R2,R3,R6,R7，这些类型分别对应不同的指令，各自的数据包结构也不同(具体内容参考SD卡协议)。这里，通过RSP_TYPE对指令cmd的opcode的解析得到相对应的reponse类型，再通过swich赋给寄存器MMC_CMDAT对应的[1:0]位。
-> 将指令和参数写入寄存器
4行writel()是整个SD卡主控制器设备驱动的实质，通过对主控制器芯片寄存器MMC_CMD,MMC_ARGH,MMC_ARGL,MMC_CMDAT的设置，实现主控制器发送指令到SD卡的功能。
四、申请中断
这里对前面的中断函数进行详细描述：
s3cmci_probe(struct platform_device *pdev)中有两个中断，一个为SD主控制器芯片内电路固有的内部中断，另一个为探测引脚的探测到外部有SD卡插拔引起的中断
1) 由主控芯片内部电路引起的中断
(request_irq(host->irq, s3cmci_irq, 0, DRIVER_NAME, host）；
回顾一下，host->irq就是刚才从platform_device里得到的中断号，
irq = platform_get_irq(pdev, 0);
host->irq = irq;
接下来，s3cmci_irq便是为该中断host->irq申请的中断函数
/*
* ISR for SDI Interface IRQ
* Communication between driver and ISR works as follows:
* host->mrq points to current request
* host->complete_what Indicates when the request is considered done
* COMPLETION_CMDSENT when the command was sent
* COMPLETION_RSPFIN when a response was received
* COMPLETION_XFERFINISH when the data transfer is finished
* COMPLETION_XFERFINISH_RSPFIN both of the above.
* host->complete_request is the completion-object the driver waits for
*
* 1) Driver sets up host->mrq and host->complete_what
* 2) Driver prepares the transfer
* 3) Driver enables interrupts
* 4) Driver starts transfer
* 5) Driver waits for host->complete_rquest
* 6) ISR checks for request status (errors and success)
* 6) ISR sets host->mrq->cmd->error and host->mrq->data->error
* 7) ISR completes host->complete_request
* 8) ISR disables interrupts
* 9) Driver wakes up and takes care of the request
*
* Note: "->error"-fields are expected to be set to 0 before the request
* was issued by mmc.c - therefore they are only set, when an error
* contition comes up
*/
static irqreturn_t s3cmci_irq(int irq, void *dev_id)
{
struct s3cmci_host *host = dev_id;
struct mmc_command *cmd;
u32 mci_csta, mci_dsta, mci_fsta, mci_dcnt, mci_imsk;
u32 mci_cclear = 0, mci_dclear;
unsigned long iflags;
mci_dsta = readl(host->base + S3C2410_SDIDSTA);
mci_imsk = readl(host->base + host->sdiimsk);
if (mci_dsta & S3C2410_SDIDSTA_SDIOIRQDETECT) {
if (mci_imsk & S3C2410_SDIIMSK_SDIOIRQ) {
mci_dclear = S3C2410_SDIDSTA_SDIOIRQDETECT;
writel(mci_dclear, host->base + S3C2410_SDIDSTA);
mmc_signal_sdio_irq(host->mmc);
return IRQ_HANDLED;
}
}
spin_lock_irqsave(&host->complete_lock, iflags);
mci_csta = readl(host->base + S3C2410_SDICMDSTAT);
mci_dcnt = readl(host->base + S3C2410_SDIDCNT);
mci_fsta = readl(host->base + S3C2410_SDIFSTA);
mci_dclear = 0;
if ((host->complete_what == COMPLETION_NONE) ||
(host->complete_what == COMPLETION_FINALIZE)) {
host->status = "nothing to complete";
clear_imask(host);
goto irq_out;
}
if (!host->mrq) {
host->status = "no active mrq";
clear_imask(host);
goto irq_out;
}
cmd = host->cmd_is_stop ? host->mrq->stop : host->mrq->cmd;
if (!cmd) {
host->status = "no active cmd";
clear_imask(host);
goto irq_out;
}
if (!s3cmci_host_usedma(host)) {
if ((host->pio_active == XFER_WRITE) &&
(mci_fsta & S3C2410_SDIFSTA_TFDET)) {
disable_imask(host, S3C2410_SDIIMSK_TXFIFOHALF);
tasklet_schedule(&host->pio_tasklet);
host->status = "pio tx";
}
if ((host->pio_active == XFER_READ) &&
(mci_fsta & S3C2410_SDIFSTA_RFDET)) {
disable_imask(host,
S3C2410_SDIIMSK_RXFIFOHALF |
S3C2410_SDIIMSK_RXFIFOLAST);
tasklet_schedule(&host->pio_tasklet);
host->status = "pio rx";
}
}
if (mci_csta & S3C2410_SDICMDSTAT_CMDTIMEOUT) {
dbg(host, dbg_err, "CMDSTAT: error CMDTIMEOUT\n");
cmd->error = -ETIMEDOUT;
host->status = "error: command timeout";
goto fail_transfer;
}
if (mci_csta & S3C2410_SDICMDSTAT_CMDSENT) {
if (host->complete_what == COMPLETION_CMDSENT) {
host->status = "ok: command sent";
goto close_transfer;
}
mci_cclear |= S3C2410_SDICMDSTAT_CMDSENT;
}
if (mci_csta & S3C2410_SDICMDSTAT_CRCFAIL) {
if (cmd->flags & MMC_RSP_CRC) {
if (host->mrq->cmd->flags & MMC_RSP_136) {
dbg(host, dbg_irq,
"fixup: ignore CRC fail with long rsp\n");
} else {
/* note, we used to fail the transfer
* here, but it seems that this is just
* the hardware getting it wrong.
*
* cmd->error = -EILSEQ;
* host->status = "error: bad command crc";
* goto fail_transfer;
*/
}
}
mci_cclear |= S3C2410_SDICMDSTAT_CRCFAIL;
}
if (mci_csta & S3C2410_SDICMDSTAT_RSPFIN) {
if (host->complete_what == COMPLETION_RSPFIN) {
host->status = "ok: command response received";
goto close_transfer;
}
if (host->complete_what == COMPLETION_XFERFINISH_RSPFIN)
host->complete_what = COMPLETION_XFERFINISH;
mci_cclear |= S3C2410_SDICMDSTAT_RSPFIN;
}
/* errors handled after this point are only relevant
when a data transfer is in progress */
if (!cmd->data)
goto clear_status_bits;
/* Check for FIFO failure */
if (host->is2440) {
if (mci_fsta & S3C2440_SDIFSTA_FIFOFAIL) {
dbg(host, dbg_err, "FIFO failure\n");
host->mrq->data->error = -EILSEQ;
host->status = "error: 2440 fifo failure";
goto fail_transfer;
}
} else {
if (mci_dsta & S3C2410_SDIDSTA_FIFOFAIL) {
dbg(host, dbg_err, "FIFO failure\n");
cmd->data->error = -EILSEQ;
host->status = "error: fifo failure";
goto fail_transfer;
}
}
if (mci_dsta & S3C2410_SDIDSTA_RXCRCFAIL) {
dbg(host, dbg_err, "bad data crc (outgoing)\n");
cmd->data->error = -EILSEQ;
host->status = "error: bad data crc (outgoing)";
goto fail_transfer;
}
if (mci_dsta & S3C2410_SDIDSTA_CRCFAIL) {
dbg(host, dbg_err, "bad data crc (incoming)\n");
cmd->data->error = -EILSEQ;
host->status = "error: bad data crc (incoming)";
goto fail_transfer;
}
if (mci_dsta & S3C2410_SDIDSTA_DATATIMEOUT) {
dbg(host, dbg_err, "data timeout\n");
cmd->data->error = -ETIMEDOUT;
host->status = "error: data timeout";
goto fail_transfer;
}
if (mci_dsta & S3C2410_SDIDSTA_XFERFINISH) {
if (host->complete_what == COMPLETION_XFERFINISH) {
host->status = "ok: data transfer completed";
goto close_transfer;
}
if (host->complete_what == COMPLETION_XFERFINISH_RSPFIN)
host->complete_what = COMPLETION_RSPFIN;
mci_dclear |= S3C2410_SDIDSTA_XFERFINISH;
}
clear_status_bits:
writel(mci_cclear, host->base + S3C2410_SDICMDSTAT);
writel(mci_dclear, host->base + S3C2410_SDIDSTA);
goto irq_out;
fail_transfer:
host->pio_active = XFER_NONE;
close_transfer:
host->complete_what = COMPLETION_FINALIZE;
clear_imask(host);
tasklet_schedule(&host->pio_tasklet);
goto irq_out;
irq_out:
dbg(host, dbg_irq,
"csta:0x%08x dsta:0x%08x fsta:0x%08x dcnt:0x%08x status:%s.\n",
mci_csta, mci_dsta, mci_fsta, mci_dcnt, host->status);
spin_unlock_irqrestore(&host->complete_lock, iflags);
return IRQ_HANDLED;
}
当调用(*request)，即host->ops->request(host, mrq)，即上文中的s3cmci_request()后，控制器与SD卡之间开始进行一次指令或数据传输，通信完毕后，主控芯片将产生一个内部中断，以告知此次指令或数据传输完毕。这个中断的具体值将保存在一个名为MMC_I_REG的中断寄存器中以供读取，中断寄存器MMC_I_REG中相关描述如下
如果中断寄存器MMC_I_REG中的第0位有值，则意味着数据传输完成，执行s3cmci_cmd_done(host, stat);
如果中断寄存器MMC_I_REG中的第2位有值，则意味着指令传输完成，执行s3cmci_data_done(host, stat);
其中stat是从状态寄存器MMC_STAT中读取的值，在代码里主要起到处理错误状态的作用。
-> s3cmci_cmd_done 收到结束指令的内部中断信号，主控制器从SD卡那里得到response，结束这次指令传输
这里需要注意，寄存器MMC_RES里已经存放了来自SD卡发送过来的response，以供读取。
2、探测引脚引起的中断
host->irq_cd = gpio_to_irq(host->pdata->gpio_detect);
if (host->irq_cd >= 0) {
if (request_irq(host->irq_cd, s3cmci_irq_cd,
IRQF_TRIGGER_RISING |
IRQF_TRIGGER_FALLING,
DRIVER_NAME, host)) {
dev_err(&pdev->dev,
"can't get card detect irq.\n");
ret = -ENOENT;
goto probe_free_gpio_cd;
}
} else {
dev_warn(&pdev->dev,
"host detect has no irq available\n");
gpio_direction_input(host->pdata->gpio_detect);
}
其中，irq_cd是通过GPIO转换得到的中断号，s3cmci_irq_cd便是该中断实现的函数
static irqreturn_t s3cmci_irq_cd(int irq, void *dev_id)
{
struct s3cmci_host *host = (struct s3cmci_host *)dev_id;
dbg(host, dbg_irq, "card detect\n");
mmc_detect_change(host->mmc, msecs_to_jiffies(500));
return IRQ_HANDLED;
}之前已经提到过mmc_detect_change，它将最终调用queue_delayed_work执行工作队列里的mmc_rescan函数。
当有SD卡插入或拔出时，硬件主控制器芯片的探测pin脚产生外部中断，进入中断处理函数，执行工作队列里的mmc_rescan，扫描SD总线，对插入或拔出SD卡作相应的处理。下文协议层将讨论mmc_rescan()。