The mmc core uses a PM notifier to temporarily during system suspend, turn off the card detection mechanism for removal/insertion of (e)MMC/SD/SDIO cards. Additionally, the notifier may be used to remove an SDIO card entirely, if a corresponding SDIO functional driver don't have the system suspend/resume callbacks assigned. This behaviour has been around for a very long time.
However, a recent bug report tells us there are problems with this approach. More precisely, when receiving the PM_SUSPEND_PREPARE notification, we may end up hanging on I/O to be completed, thus also preventing the system from getting suspended.
In the end what happens, is that the cancel_delayed_work_sync() in mmc_pm_notify() ends up waiting for mmc_rescan() to complete - and since mmc_rescan() wants to claim the host, it needs to wait for the I/O to be completed first.
Typically, this problem is triggered in Android, if there is ongoing I/O while the user decides to suspend, resume and then suspend the system again. This due to that after the resume, an mmc_rescan() work gets punted to the workqueue, which job is to verify that the card remains inserted after the system has resumed.
To fix this problem, userspace needs to become frozen to suspend the I/O, prior to turning off the card detection mechanism. Therefore, let's drop the PM notifiers for mmc subsystem altogether and rely on the card detection to be turned off/on as a part of the system_freezable_wq, that we are already using.
Moreover, to allow and SDIO card to be removed during system suspend, let's manage this from a ->prepare() callback, assigned at the mmc_host_class level. In this way, we can use the parent device (the mmc_host_class device), to remove the card device that is the child, in the device_prepare() phase.
Reported-by: Kiwoong Kim kwmad.kim@samsung.com Cc: stable@vger.kernel.org Signed-off-by: Ulf Hansson ulf.hansson@linaro.org
Reviewed-by: Kiwoong Kim kwmad.kim@samsung.com
Thanks. Kiwoong Kim