linux2.6内核SD Card Driver详细解析之一

linux2.6内核SD Card Driver详细解析之一

来自：CSDN博客   |  时间：2012-03-18 20:27:48  |   相似文章(0)

原文链接： http://blog.csdn.net/wavemcu/article/details/7366852

一：MMC/SD/SDIO的概念

1. MMC：(Multi Media Card)由西门子公司和首推CF的SanDisk于1997年推出的多媒体记忆卡标准。

2. SD：(Secure Digital Memory Card)由日本松下、东芝及美国SanDisk公司于1999年8月共同开发研制的新一代记忆卡标准，已完全兼容MMC标准。

3. SDIO：(Secure Digital Input and Output Card)安全数字输入输出卡。SDIO是在SD标准上定义了一种外设接口，通过SD的I/O接脚来连接外围设备，并且通过SD上的 I/O数据接位与这些外围设备进行数据传输。是目前较热门的技术，如下图中的一些设备：GPS、相机、Wi-Fi、调频广播、条形码读卡器、蓝牙等。

4. 工作模式：工作模式是针对主机控制器来说的。SDI控制器可以在符合MMC的标准下工作，或者可以在符合SD的标准下工作，或者可以在符合SDIO的标准下工作。故就分别简称为：MMC模式、SD模式和SDIO模式。

5. 传输模式：传输模式也是针对主机控制器来说的，指控制器与卡之间数据的传输模式，或者说是总线类型。SDI控制器可支持SPI、1位和4位的三种传输模式(总线类型)。至于1位和4位又是什么意思呢？他们是指传输数据总线的线宽，具体参考数据手册。

下面使用表格列出了MMC、SD、SDIO的电气特性及性能和不同工作模式下支持的传输模式情况：

二： MMC/SD协议

根据协议，MMC/SD卡的驱动被分为：卡识别阶段和数据传输阶段。在卡识别阶段通过命令使MMC/SD处于：空闲(idle)、准备(ready)、识别(ident)、等待(stby)、不活动(ina)几种不同的状态；而在数据传输阶段通过命令使MMC/SD处于：发送(data)、传输(tran)、接收(rcv)、程序(prg)、断开连接(dis)几种不同的状态。所以可以总结MMC/SD在工作的整个过程中分为两个阶段和十种状态。下面使用图形来描述一下在两个阶段中这十种状态之间的转换关系。

卡识别阶段，如下图：

【图是从网络上抓取】

数据传输阶段，如下图：

【图是从网络上抓取】

MMC/SD设备驱动代码在Linux源码中的位置/linux-2.6.35.4/drivers/mmc/，分别有card、core和host三个文件夹，他们都是MMC/SD卡的驱动。在实际驱动开发中，只需要在host文件夹下实现你具体的MMC/SD设备驱动部分代码，也就是控制器(支持对MMC/SD卡的控制，俗称MMC/SD主机控制器)和SDI控制器与MMC/SD卡的硬件接口电路。同时card、core和host这三层的关系，我们用一幅图来进行描述，图如下：

【图是从网络上抓取】

从图中的关系可以看出，整个MMC/SD模块中最重要的部分是Core核心层，他提供了一系列的接口函数，对上提供了将主机驱动注册到系统，给应用程序提供设备访问接口，对下提供了对主机控制器控制的方法及块设备请求的支持。

三： 分析MMC/SD卡设备驱动程序

1. MMC/SD卡驱动程序的重要数据结构mmc_host，该结构位于Core核心层，主要用于核心层与主机驱动层的数据交换处理。定义在/include/linux/mmc/host.h中：

struct mmc_host {
	struct device		*parent;
	struct device		class_dev;
	int			index;
	const struct mmc_host_ops *ops;
	unsigned int		f_min;
	unsigned int		f_max;
	u32			ocr_avail;

#define MMC_VDD_165_195		0x00000080	/* VDD voltage 1.65 - 1.95 */
#define MMC_VDD_20_21		0x00000100	/* VDD voltage 2.0 ~ 2.1 */
#define MMC_VDD_21_22		0x00000200	/* VDD voltage 2.1 ~ 2.2 */
#define MMC_VDD_22_23		0x00000400	/* VDD voltage 2.2 ~ 2.3 */
#define MMC_VDD_23_24		0x00000800	/* VDD voltage 2.3 ~ 2.4 */
#define MMC_VDD_24_25		0x00001000	/* VDD voltage 2.4 ~ 2.5 */
#define MMC_VDD_25_26		0x00002000	/* VDD voltage 2.5 ~ 2.6 */
#define MMC_VDD_26_27		0x00004000	/* VDD voltage 2.6 ~ 2.7 */
#define MMC_VDD_27_28		0x00008000	/* VDD voltage 2.7 ~ 2.8 */
#define MMC_VDD_28_29		0x00010000	/* VDD voltage 2.8 ~ 2.9 */
#define MMC_VDD_29_30		0x00020000	/* VDD voltage 2.9 ~ 3.0 */
#define MMC_VDD_30_31		0x00040000	/* VDD voltage 3.0 ~ 3.1 */
#define MMC_VDD_31_32		0x00080000	/* VDD voltage 3.1 ~ 3.2 */
#define MMC_VDD_32_33		0x00100000	/* VDD voltage 3.2 ~ 3.3 */
#define MMC_VDD_33_34		0x00200000	/* VDD voltage 3.3 ~ 3.4 */
#define MMC_VDD_34_35		0x00400000	/* VDD voltage 3.4 ~ 3.5 */
#define MMC_VDD_35_36		0x00800000	/* VDD voltage 3.5 ~ 3.6 */

	unsigned long		caps;		/* Host capabilities */

#define MMC_CAP_4_BIT_DATA	(1 << 0)	/* Can the host do 4 bit transfers */
#define MMC_CAP_MMC_HIGHSPEED	(1 << 1)	/* Can do MMC high-speed timing */
#define MMC_CAP_SD_HIGHSPEED	(1 << 2)	/* Can do SD high-speed timing */
#define MMC_CAP_SDIO_IRQ	(1 << 3)	/* Can signal pending SDIO IRQs */
#define MMC_CAP_SPI		(1 << 4)	/* Talks only SPI protocols */
#define MMC_CAP_NEEDS_POLL	(1 << 5)	/* Needs polling for card-detection */
#define MMC_CAP_8_BIT_DATA	(1 << 6)	/* Can the host do 8 bit transfers */
#define MMC_CAP_DISABLE		(1 << 7)	/* Can the host be disabled */
#define MMC_CAP_NONREMOVABLE	(1 << 8)	/* Nonremovable e.g. eMMC */
#define MMC_CAP_WAIT_WHILE_BUSY	(1 << 9)	/* Waits while card is busy */

	mmc_pm_flag_t		pm_caps;	/* supported pm features */

	/* host specific block data */
	unsigned int		max_seg_size;	/* see blk_queue_max_segment_size */
	unsigned short		max_hw_segs;	/* see blk_queue_max_hw_segments */
	unsigned short		max_phys_segs;	/* see blk_queue_max_phys_segments */
	unsigned short		unused;
	unsigned int		max_req_size;	/* maximum number of bytes in one req */
	unsigned int		max_blk_size;	/* maximum size of one mmc block */
	unsigned int		max_blk_count;	/* maximum number of blocks in one req */

	/* private data */
	spinlock_t		lock;		/* lock for claim and bus ops */

	struct mmc_ios		ios;		/* current io bus settings */
	u32			ocr;		/* the current OCR setting */

	/* group bitfields together to minimize padding */
	unsigned int		use_spi_crc:1;
	unsigned int		claimed:1;	/* host exclusively claimed */
	unsigned int		bus_dead:1;	/* bus has been released */
#ifdef CONFIG_MMC_DEBUG
	unsigned int		removed:1;	/* host is being removed */
#endif

	/* Only used with MMC_CAP_DISABLE */
	int			enabled;	/* host is enabled */
	int			nesting_cnt;	/* "enable" nesting count */
	int			en_dis_recurs;	/* detect recursion */
	unsigned int		disable_delay;	/* disable delay in msecs */
	struct delayed_work	disable;	/* disabling work */

	struct mmc_card		*card;		/* device attached to this host */

	wait_queue_head_t	wq;
	struct task_struct	*claimer;	/* task that has host claimed */
	int			claim_cnt;	/* "claim" nesting count */

	struct delayed_work	detect;

	const struct mmc_bus_ops *bus_ops;	/* current bus driver */
	unsigned int		bus_refs;	/* reference counter */

	unsigned int		sdio_irqs;
	struct task_struct	*sdio_irq_thread;
	atomic_t		sdio_irq_thread_abort;

	mmc_pm_flag_t		pm_flags;	/* requested pm features */

#ifdef CONFIG_LEDS_TRIGGERS
	struct led_trigger	*led;		/* activity led */
#endif

	struct dentry		*debugfs_root;

	unsigned long		private[0] ____cacheline_aligned;
};

2. MMC/SD卡驱动程序的重要数据结构mmc_host_ops，主要用于HOST端命令请求，直接跟芯片中SD卡寄存器打交道，定义在/include/linux/mmc/host.h中：

struct mmc_host_ops {
	/*
	 * Hosts that support power saving can use the 'enable' and 'disable'
	 * methods to exit and enter power saving states. 'enable' is called
	 * when the host is claimed and 'disable' is called (or scheduled with
	 * a delay) when the host is released. The 'disable' is scheduled if
	 * the disable delay set by 'mmc_set_disable_delay()' is non-zero,
	 * otherwise 'disable' is called immediately. 'disable' may be
	 * scheduled repeatedly, to permit ever greater power saving at the
	 * expense of ever greater latency to re-enable. Rescheduling is
	 * determined by the return value of the 'disable' method. A positive
	 * value gives the delay in milliseconds.
	 *
	 * In the case where a host function (like set_ios) may be called
	 * with or without the host claimed, enabling and disabling can be
	 * done directly and will nest correctly. Call 'mmc_host_enable()' and
	 * 'mmc_host_lazy_disable()' for this purpose, but note that these
	 * functions must be paired.
	 *
	 * Alternatively, 'mmc_host_enable()' may be paired with
	 * 'mmc_host_disable()' which calls 'disable' immediately.  In this
	 * case the 'disable' method will be called with 'lazy' set to 0.
	 * This is mainly useful for error paths.
	 *
	 * Because lazy disable may be called from a work queue, the 'disable'
	 * method must claim the host when 'lazy' != 0, which will work
	 * correctly because recursion is detected and handled.
	 */
	int (*enable)(struct mmc_host *host);
	int (*disable)(struct mmc_host *host, int lazy);
	void	(*request)(struct mmc_host *host, struct mmc_request *req);
	/*
	 * Avoid calling these three functions too often or in a "fast path",
	 * since underlaying controller might implement them in an expensive
	 * and/or slow way.
	 *
	 * Also note that these functions might sleep, so don't call them
	 * in the atomic contexts!
	 *
	 * Return values for the get_ro callback should be:
	 *   0 for a read/write card
	 *   1 for a read-only card
	 *   -ENOSYS when not supported (equal to NULL callback)
	 *   or a negative errno value when something bad happened
	 *
	 * Return values for the get_cd callback should be:
	 *   0 for a absent card
	 *   1 for a present card
	 *   -ENOSYS when not supported (equal to NULL callback)
	 *   or a negative errno value when something bad happened
	 */
	void	(*set_ios)(struct mmc_host *host, struct mmc_ios *ios);
	int	(*get_ro)(struct mmc_host *host);
	int	(*get_cd)(struct mmc_host *host);

	void	(*enable_sdio_irq)(struct mmc_host *host, int enable);

	/* optional callback for HC quirks */
	void	(*init_card)(struct mmc_host *host, struct mmc_card *card);
};

对于mmc_host_ops需要重点讲一下：

void	(*request)(struct mmc_host *host, struct mmc_request *req);

这个函数主要用于SD卡命令的传输，比如发送和接收命令，CMD0,CMD8,ACMD41诸如此类的都是在这个函数去实现。

void	(*set_ios)(struct mmc_host *host, struct mmc_ios *ios);

这个函数主要用于设置SD卡的CLK，MMC_POWER_OFF，MMC_POWER_ON的一些初始化。

int	(*get_ro)(struct mmc_host *host);

这个函数主要用于检测SD卡的写保护是否打开。

int	(*get_cd)(struct mmc_host *host);

这个函数主要用于SD卡的检测，是否有卡插入和弹出。

3. MMC/SD卡驱动程序的重要函数mmc_alloc_host，用于分配mmc_host结构体指针的内存空间大小，定义在host.c中：

struct mmc_host *mmc_alloc_host(int extra, struct device *dev)
{
	int err;
	struct mmc_host *host;

	if (!idr_pre_get(&mmc_host_idr, GFP_KERNEL))
		return NULL;

	host = kzalloc(sizeof(struct mmc_host) + extra, GFP_KERNEL);
	if (!host)
		return NULL;

	spin_lock(&mmc_host_lock);
	err = idr_get_new(&mmc_host_idr, host, &host->index);
	spin_unlock(&mmc_host_lock);
	if (err)
		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);

	spin_lock_init(&host->lock);
	init_waitqueue_head(&host->wq);
	INIT_DELAYED_WORK(&host->detect, mmc_rescan);
	INIT_DELAYED_WORK_DEFERRABLE(&host->disable, mmc_host_deeper_disable);

	/*
	 * By default, hosts do not support SGIO or large requests.
	 * They have to set these according to their abilities.
	 */
	host->max_hw_segs = 1;
	host->max_phys_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;

而在mmc_alloc_host函数中被调用的mmc_rescan函数，这个是需要 重点关注的，因为SD卡协议中的检测，以及卡识别等都是在此函数中实现，具体的代码如下：

void mmc_rescan(struct work_struct *work)
{
	struct mmc_host *host =
		container_of(work, struct mmc_host, detect.work);
	u32 ocr;
	int err;

	mmc_bus_get(host);

	/* if there is a card registered, check whether it is still present */
	if ((host->bus_ops != NULL) && host->bus_ops->detect && !host->bus_dead)
		host->bus_ops->detect(host);

	mmc_bus_put(host);


	mmc_bus_get(host);

	/* if there still is a card present, stop here */
	if (host->bus_ops != NULL) {
		mmc_bus_put(host);
		goto out;
	}

	/* detect a newly inserted card */

	/*
	 * Only we can add a new handler, so it's safe to
	 * release the lock here.
	 */
	mmc_bus_put(host);

	if (host->ops->get_cd && host->ops->get_cd(host) == 0)
		goto out;

	mmc_claim_host(host);

	mmc_power_up(host);
	sdio_reset(host);
	mmc_go_idle(host); //让SD卡处于IDL_STATUS

	mmc_send_if_cond(host, host->ocr_avail); //检测SD卡是否支持SD2.0

	/*
	 * First we search for SDIO...
	 */
	err = mmc_send_io_op_cond(host, 0, &ocr); //检测是否是支持SDIO的卡，比如：SDIO WIFI等.
	if (!err) {
		if (mmc_attach_sdio(host, ocr))
			mmc_power_off(host);
		goto out;
	}

	/*
	 * ...then normal SD...
	 */
	err = mmc_send_app_op_cond(host, 0, &ocr); //检测是否是支持标准的SD卡.
	if (!err) {
		if (mmc_attach_sd(host, ocr))
			mmc_power_off(host);
		goto out;
	}

	/*
	 * ...and finally MMC.
	 */
	err = mmc_send_op_cond(host, 0, &ocr); //最后才是检测是否是支持MMC的卡
	if (!err) {
		if (mmc_attach_mmc(host, ocr))
			mmc_power_off(host);
		goto out;
	}

	mmc_release_host(host);
	mmc_power_off(host);

out:
	if (host->caps & MMC_CAP_NEEDS_POLL)
		mmc_schedule_delayed_work(&host->detect, HZ);
}

4. MMC/SD卡驱动程序的重要函数mmc_add_host，用于挂载一个mmc_host到内核，定义在host.c中：

int mmc_add_host(struct mmc_host *host)
{
	int err;

	WARN_ON((host->caps & MMC_CAP_SDIO_IRQ) &&
		!host->ops->enable_sdio_irq);

	led_trigger_register_simple(dev_name(&host->class_dev), &host->led);

	err = device_add(&host->class_dev);
	if (err)
		return err;

#ifdef CONFIG_DEBUG_FS
	mmc_add_host_debugfs(host);
#endif

	mmc_start_host(host);

	return 0;
}

可以从SD卡平台驱动看到上面函数的调用情况：

static int __devinit s3cmci_probe(struct platform_device *pdev)
{

   struct s3cmci_host *host;
   //实例一个名为mmc的结构体指针，用于与Core核心层中的mmc_host结构体指针相关联
   struct mmc_host    *mmc;
   int ret;

   spin_lock_init(&host->complete_lock);

   //分配mmc_host结构体指针的内存空间大小，该函数在host.c中实现，这里要注意一点，为什么参数
   //是s3cmci_host结构体的大小，到host.c中看，实际这里分配的是mmc_host加s3cmci_host的大小。
   mmc = mmc_alloc_host(sizeof(struct s3cmci_host), &pdev->dev);
   if (!mmc)  
   {
       ret = -ENOMEM;
       goto probe_out;
   }

   //调用mmc_priv函数将mmc_host和s3cmci_host结构体的对象关联起来，mmc_priv定义在host.h中
   host = mmc_priv(mmc);

   //下面就开始初始化s3cmci_host结构体的各成员
   host->mmc     = mmc;
   host->pdev    = pdev;
   host->pdata   = pdev->dev.platform_data;    

   ..................................
   ..................................
   ..................................

   //下面对mmc_host进行初始化
mmc->ops       = &s3cmci_ops;   //SDI主机控制器操作结构体
   mmc->ocr_avail = MMC_VDD_32_33 | MMC_VDD_33_34;   //设置工作电压范围
   mmc->caps      = MMC_CAP_4_BIT_DATA;              //设置总线宽度为4位
   mmc->f_min     = host->clk_rate / (host->clk_div * 256); //设置最小工作频率
   mmc->f_max     = host->clk_rate / host->clk_div;  //设置最大工作频率
   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_phys_segs  = 128;
   mmc->max_hw_segs    = 128;

   //将SDI host设备注册到系统中
 ret = mmc_add_host(mmc);
   if (ret)  
   {
       dev_err(&pdev->dev, "failed to add mmc host./n");
       goto free_cpufreq;
   }

   //将SDI host设备的数据赋值给系统平台设备
   platform_set_drvdata(pdev, mmc);

   return 0;
  ..................................
  ..................................
  ..................................

probe_free_host:
   mmc_free_host(mmc);
probe_out:
   return ret;
}

未完待续.............................