> On 2018Jul26, at 01:59, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Wed, 25 Jul 2018, Kai-Heng Feng wrote: > >> In order to let host's parent device, rtsx_usb, to use USB remote wake >> up signaling to do card detection, it needs to be suspended. Hence it's >> necessary to add runtime PM support for the memstick host. >> >> To keep memstick host stays suspended when it's not in use, convert the >> card detection function from kthread to delayed_work, which can be >> scheduled when the host is resumed and can be canceled when the host is >> suspended. >> >> Use an idle function check if there's no card and the power mode is >> MEMSTICK_POWER_OFF. If both criteria are met, put the device to suspend. >> >> Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx> > > I'm not familiar enough with this driver to comment on specific > instances, but you should carefully go through the code and make sure > that you use pm_runtime_get_noresume() and pm_runtime_put_noidle() > correctly. > > The basic idea is to use these when you know beforehand that the device > is already at full power (for _get_noresume) and the usage count will > not go to 0 (for _put_noidle). If you aren't certain of these > requirements then you should call pm_runtime_get_sync() and > pm_runtime_put(). There are two different uses for pm_runtime helpers. The first use case is to prevent parent device, rtsx_usb, from suspending: pm_runtime_get_noresume() rtsx_usb_read_register() pm_runtime_put_noidle() The second use case, to manage memstick host itself. memstick_detect_change() powers the host on if there’s a card in slot, and it powers host off when there’s no card. Once memstick_detect_change() is done, we can check if the host can be suspended. So we are sure the timing when the power is on or off. Kai-Heng > > Alan Stern > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
