Hi, I found the mmc_rescan function is called periodically. and the only place I can see the name is this line below in the mmc_alloc_host function INIT_DELAYED_WORK(&host->detect, mmc_rescan); so it is regsitered as a delayed work in mmc_host. And at the end of mmc_rescan, I see mmc_schedule_delayed_work(&host->detect, HZ); Q1 : Is this how it is called periodically every second? I guess so.. In the SD host driver, in initial slot initialization, there is mcc_host_add which eventually schedules mmc_rescan. (mmc_add_host -> mmc_start_host -> mmc_detect_change -> mmc_schedule_delayed_work(&host->detect, delay)) and towards the end of this initial slot initialization, there is queue_work(my_workqueue, &host->card_work); And the card_work is a function supposed to be called when a card is inserted or removed. In the card_work, there is at the end mmc_detect_change(slot->mmc, msecs_to_jiffies(host->pdata->detect_delay_ms)); and inside mmc_detect_change, mmc_schedule_delayed_work(&host->detect, delay); is called which is mmc_rescan. Q2 : Is there something wrong (mmc_rescan is started and schedule itself by mmc_add_host, but it is started by another card_work)? I tried removing queue_work and it still seems to work.. can anybody confirm or tell me anything? best regards, Chan