linux2.6内核SD Card Driver详细解析之一

http://blog.csdn.net/wavemcu/article/details/7366852

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作者：EasyWave                                                                                 时间：2012.03.18

类别：linux驱动开发                                                                           声明：转载，请保留链接

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