INIT_DELAYED_WORK

使用步骤：
    1、INIT_DELAYED_WORK(&host->detect, mmc_rescan);
    struct delayed_work {//&host->detect 的定义就是delayed_work
            struct work_struct work = {
                atomic_long_t data;        //WORK_DATA_INIT
                struct list_head entry;     //INIT_LIST_HEAD(&(_work)->entry);
                work_func_t func;          //mmc_rescan
            };
            struct timer_list timer; //__setup_timer(&timer, delayed_work_timer_fn,(unsigned long)(delayed_work),
            /* target workqueue and CPU ->timer uses to queue ->work */
            struct workqueue_struct *wq;
            int cpu;
    };
    2、queue_delayed_work(workqueue, work, delay);