linux2.6内核SD Card Driver详细解析之一

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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 deviceclass_dev;intindex;const struct mmc_host_ops *ops;unsigned intf_min;unsigned intf_max;u32ocr_avail;#define MMC_VDD_165_1950x00000080/* VDD voltage 1.65 - 1.95 */#define MMC_VDD_20_210x00000100/* VDD voltage 2.0 ~ 2.1 */#define MMC_VDD_21_220x00000200/* VDD voltage 2.1 ~ 2.2 */#define MMC_VDD_22_230x00000400/* VDD voltage 2.2 ~ 2.3 */#define MMC_VDD_23_240x00000800/* VDD voltage 2.3 ~ 2.4 */#define MMC_VDD_24_250x00001000/* VDD voltage 2.4 ~ 2.5 */#define MMC_VDD_25_260x00002000/* VDD voltage 2.5 ~ 2.6 */#define MMC_VDD_26_270x00004000/* VDD voltage 2.6 ~ 2.7 */#define MMC_VDD_27_280x00008000/* VDD voltage 2.7 ~ 2.8 */#define MMC_VDD_28_290x00010000/* VDD voltage 2.8 ~ 2.9 */#define MMC_VDD_29_300x00020000/* VDD voltage 2.9 ~ 3.0 */#define MMC_VDD_30_310x00040000/* VDD voltage 3.0 ~ 3.1 */#define MMC_VDD_31_320x00080000/* VDD voltage 3.1 ~ 3.2 */#define MMC_VDD_32_330x00100000/* VDD voltage 3.2 ~ 3.3 */#define MMC_VDD_33_340x00200000/* VDD voltage 3.3 ~ 3.4 */#define MMC_VDD_34_350x00400000/* VDD voltage 3.4 ~ 3.5 */#define MMC_VDD_35_360x00800000/* VDD voltage 3.5 ~ 3.6 */unsigned longcaps;/* 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_tpm_caps;/* supported pm features *//* host specific block data */unsigned intmax_seg_size;/* see blk_queue_max_segment_size */unsigned shortmax_hw_segs;/* see blk_queue_max_hw_segments */unsigned shortmax_phys_segs;/* see blk_queue_max_phys_segments */unsigned shortunused;unsigned intmax_req_size;/* maximum number of bytes in one req */unsigned intmax_blk_size;/* maximum size of one mmc block */unsigned intmax_blk_count;/* maximum number of blocks in one req *//* private data */spinlock_tlock;/* lock for claim and bus ops */struct mmc_iosios;/* current io bus settings */u32ocr;/* the current OCR setting *//* group bitfields together to minimize padding */unsigned intuse_spi_crc:1;unsigned intclaimed:1;/* host exclusively claimed */unsigned intbus_dead:1;/* bus has been released */#ifdef CONFIG_MMC_DEBUGunsigned intremoved:1;/* host is being removed */#endif/* Only used with MMC_CAP_DISABLE */intenabled;/* host is enabled */intnesting_cnt;/* "enable" nesting count */inten_dis_recurs;/* detect recursion */unsigned intdisable_delay;/* disable delay in msecs */struct delayed_workdisable;/* disabling work */struct mmc_card*card;/* device attached to this host */wait_queue_head_twq;struct task_struct*claimer;/* task that has host claimed */intclaim_cnt;/* "claim" nesting count */struct delayed_workdetect;const struct mmc_bus_ops *bus_ops;/* current bus driver */unsigned intbus_refs;/* reference counter */unsigned intsdio_irqs;struct task_struct*sdio_irq_thread;atomic_tsdio_irq_thread_abort;mmc_pm_flag_tpm_flags;/* requested pm features */#ifdef CONFIG_LEDS_TRIGGERSstruct led_trigger*led;/* activity led */#endifstruct dentry*debugfs_root;unsigned longprivate[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_STATUSmmc_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_FSmmc_add_host_debugfs(host);#endifmmc_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.............................