Linux MMC子系統（1）– MMC Host層（2.6.28)

Linux 的 MMC驅動主要管理MMC卡/SD卡，從上到下分為了MMC裝置層，MMC Core層，MMC Host層，Host層負責底層硬體：

如下：
        /dev下裝置檔案訪問MMC/SD/SDIO
使用者空間             |
---------------------|-----------------------------------------------------
核心空間            \ /
         MMC Card層(對應具體的裝置驅動，如MMC/SD卡塊裝置驅動，SDIO UART)
                     |
                    \ /
          MMC core層(為上次裝置驅動實現提供操作介面，和下層host註冊提供機制)
                     |
                    \ /
           Host層(具體MMC/SD/SDIO控制器驅動層。如S3C2440 MMC/SD控制器驅動)
                     |
                    \ /
-----------------------------------------------------------------------------
                    硬體層

這節主要介紹MMC Host層，以S3C2440驅動為例，檔案/drivers/mmc/host/s3cmci.c 檔案實現的介面。

MMC Core與Host層的溝通橋樑為：

struct mmc_host {

         structdevice             *parent;

         structdevice             class_dev;

         int                       index;

         const  struct mmc_host_ops *ops;             //Host層需要實現的介面

         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);
    
        /*這個是關鍵的函數，所有對MMC/SD的操作，包括髮命令和讀資料，都通過該介面來實現，所以實現該介面時要處理是命令還是資料操作，另外要考慮是否使用DMA來進行資料轉送。/用於命令和資料的發送接收    */
    void    (*request)(struct mmc_host *host, struct mmc_request *req);
        /*用來設定MMC/SD的時鐘，電壓等操作IO,初始化的操作*/
    void    (*set_ios)(struct mmc_host *host, struct mmc_ios *ios);
        /*檢查MMC/SD是否防寫保護了    */
    int    (*get_ro)(struct mmc_host *host);
        /*檢查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);
};

那麼在s3cmci.c檔案中 根據以上介面分別進行了實現，以上的mm_host通過Core層的mmc_add_host函數添加下面一節介紹Core層