Linux MMC子系统（1）-- MMC Host层（2.6.28)-优快云博客

Linux 的 MMC驱动主要管理MMC卡/SD卡，从上到下分为了MMC设备层，MMC Core层，MMC Host层，Host层负责底层硬件：

如下：
        /dev下设备文件访问MMC/SD/SDIO
用户空间             |
---------------------|-----------------------------------------------------
内核空间            \ /
         MMC Card层(对应具体的设备驱动，如MMC/SD卡块设备驱动，SDIO UART)
                     |
                    \ /
          MMC core层(为上次设备驱动实现提供操作接口，和下层host注册提供机制)
                     |
                    \ /
           Host层(具体MMC/SD/SDIO控制器驱动层。如S3C2440 MMC/SD控制器驱动)
                     |
                    \ /
-----------------------------------------------------------------------------
                    硬件层

这节主要介绍MMC Host层，以S3C2440驱动为例，文件/drivers/mmc/host/s3cmci.c 文件实现的接口。

MMC Core与Host层的沟通桥梁为：

struct mmc_host {

structdevice *parent;

structdevice class_dev;

int index;

const struct mmc_host_ops *ops; //Host层需要实现的接口

unsignedint f_min;

unsignedint f_max;

u32 ocr_avail;

unsignedlong caps; /* Host capabilities */

/*host specific block data */

unsignedint max_seg_size; /* see blk_queue_max_segment_size */

unsignedshort max_hw_segs; /* see blk_queue_max_hw_segments */

unsignedshort max_phys_segs; /* see blk_queue_max_phys_segments */

unsignedshort unused;

unsignedint max_req_size; /* maximum number of bytes in one req*/

unsignedint max_blk_size; /* maximum size of one mmc block */

unsignedint max_blk_count; /* maximum number of blocks in one req */

/*private data */

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

structmmc_ios ios; /* current io bus settings */

u32 ocr; /* the current OCR setting */

/*group bitfields together to minimize padding */

unsignedint use_spi_crc:1;

unsignedint claimed:1; /* host exclusively claimed */

unsignedint bus_dead:1; /* bus has been released */

structmmc_card *card; /* device attached to this host*/

wait_queue_head_t wq;

structdelayed_work detect;

conststruct mmc_bus_ops *bus_ops; /* currentbus driver */

unsignedint bus_refs; /* reference counter */

unsignedint sdio_irqs;

structtask_struct *sdio_irq_thread;

atomic_t sdio_irq_thread_abort;

structdentry *debugfs_root;

unsignedlong private[0]____cacheline_aligned;

};

struct mmc_host_ops {
    /*使能和禁止HOST控制器*/
    int (*enable)(struct mmc_host *host);
    int (*disable)(struct mmc_host *host, int lazy);

        /*这个是关键的函数，所有对MMC/SD的操作，包括发命令和读数据，都通过该接口来实现，所以实现该接口时要处理是命令还是数据操作，另外要考虑是否使用DMA来进行数据传输。/用于命令和数据的发送接收    */
    void    (*request)(struct mmc_host *host, struct mmc_request *req);
        /*用来设置MMC/SD的时钟，电压等操作IO,初始化的操作*/
    void    (*set_ios)(struct mmc_host *host, struct mmc_ios *ios);
        /*检查MMC/SD是否写保护了    */
    int    (*get_ro)(struct mmc_host *host);
        /*检查mmc/sd的插入和拔出    */
    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);
};