On 14 June 2013 22:52, Colin Cross <ccross@xxxxxxxxxxx> wrote: > On Fri, Jun 14, 2013 at 11:42 AM, Zoran Markovic > <zoran.markovic@xxxxxxxxxx> wrote: >>> I am not sure I understand why this patch is needed. When a new card >>> is inserted/removed and the upper levels gets notification about the >>> new card, triggering the mounting/un-mounting of the file system, why >>> should it be the lowest layer (mmc) that prevents the platform from >>> enter suspend/sleep? Why do we need to prevent it at all? >>> >>> Note that notifier handling in mmc_pm_notify, was if I remember >>> correctly, not completely developed when the original version of this >>> patch was being discussed. mmc_pm_notify prevents cards from being >>> inserted/removed in the middle of suspend->resume sequence, is that >>> not enough? >> >> I will try to speak on behalf of the original implementers in a hope >> they would provide the original motivation for the patch. >> >> My understanding is that any preemption in the procedure could be an >> opportunity to suspend, as there may be a suspend request racing with >> this code. This is why the calls to __pm_stay_awake() and >> queue_delayed_work() are so tightly coupled. It would be up to the >> delayed work procedure (mmc_rescan()) to decide whether or not it is >> safe to suspend. If there are no changes in the MMC state or all >> changes can be handled by mmc_rescan(), it is safe to call >> __pm_relax(). Otherwise, userland may take over processing of this >> event, and this is why the awake state needs to be extended by 1/2 >> second. > > The __pm_stay_awake() is required to prevent autosleep during the time > between the card detect interrupt and when the userspace process that > gets the notification runs. The 1/2 second delay is used because it > is easier than trying to detect when the userspace process has > received the notification, at which time it should hold its own > wakelock and the mmc subsystem can call __pm_relax(). Hi Colin, I don't have the in-depth knowledge about how the userspace deamons handles the event notifications, so please bare with me while I am trying to understand more here. First of all, are we trying to solve an issue here or just improving some specific situation, that is not clear to me. I might have misunderstood this patch, but it seems like your concern is that you believe the event notification can get lost - if userspace are about to trigger a suspend while a card is being inserted/removed. If that is the case, could you elaborate on what level the notification can get lost? Kind regards Ulf Hansson -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
