On Tue, 13 May 2014, Rafael J. Wysocki wrote: > Hi All, > > We've discussed that at length here: > > http://marc.info/?t=139950469000003&r=1&w=4 > > but I'm starting a new thread to refresh things a bit. > > This is about adding a mechanism allowing us to avoid runtime-suspended > devices during system suspend. The reason why it has to touch the PM core > is because that needs to be coordinated across the device hierarchy. > > The idea is to add a new device PM flag and to modify the PM core as follows. > > - If ->prepare() returns a positive number for a device, that means "this > device is runtime-suspended and you can leave it like that if you do the > same for all of its descendants". > > - If that happens, the PM core sets the new flag for the device in > question *if* the device is indeed runtime-suspended *and* *if* > the transition is a suspend (and not hibernation, for example). > Otherwise, it clears the flag for the device. All of that happens in > device_prepare(). > > - In __device_suspend() the PM core clears the new flag for the device's > parent if it is clear for the device to ensure that the flag will only > be set for a device if it is also set for all of its descendants. There's nothing to prevent a runtime-suspended device from being resumed in between the ->prepare() and ->suspend() callbacks. (Ulf mentioned this too.) Therefore it makes little sense to check the device's runtime status in device_prepare(). The check should be done in __device_suspend(). > - PM core skips ->suspend/late/noirq and ->resume/early/noirq for all devices > having the flag set - so the flag can be called "direct_complete" as it > causes the PM core to go directy for the ->complete() callback when set. > > - The ->complete() callback has to check direct_complete if ->prepare() > returned a positive number previously and is responsible for further > handling of the device. > > That is introduced by patch [2/3]. > > To simplify things slightly it is helpful to move the invocation of > pm_runtime_barrier() from __device_suspend() to device_prepare(), but still > under pm_runtime_get_noresume() beforehand (patch [1/3]). If the check is moved to __device_suspend() then the barrier can remain where it is now. > Patch [3/3] shows how this can be used by adding support for it to the ACPI > PM comain. > > Thanks! Aside from this one matter, everything seems pretty good. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
