On Mon, 29 Jun 2009, Rafael J. Wysocki wrote: > IMO one can think of pm_request_resume() as a top half of pm_runtime_resume(). Normal top halves don't trigger before the circumstances are appropriate. For example, if you enable remote wakeup on a USB device, it won't send a wakeup signal before it has been powered down. A driver calling pm_request_resume while the device is still resumed is like a USB device sending a wakeup request while it is still powered up. So IMO the analogy with top halves isn't a good one. > Thus, it should either queue up a request to run pm_runtime_resume() or leave > the status as though pm_runtime_resume() ran. Anything else would be > internally inconsistent. So, if pm_runtime_resume() cancels pending suspend > requests, pm_request_resume() should do the same or the other way around. > > Now, arguably, ignoring pending suspend requests is somewhat easier from > the core's point of view, but it may not be so for drivers. The argument I gave in the previous email demonstrates that it doesn't make any difference to drivers. Either way, they have to use two I/O pathways, they have to do a pm_runtime_get before pm_request_resume, and they have to do a pm_request_put after the I/O is done. Of course, this is all somewhat theoretical. I still don't know of any actual drivers that do the equivalent of pm_request_resume. > My point is that the core should always treat pending suspend requests in the > same way. If they are canceled by pm_runtime_resume(), then > pm_request_resume() should also cancel them and it shouldn't be possible > to schedule a suspend request when the resume counter is greater than 0. > In turn, if they are ignored by pm_runtime_resume(), then pm_request_resume() > should also ignore them and there's no point to prevent pm_request_suspend() > from scheduling a suspend request if the resume counter is greater than 0. > > Any other type of behavior has a potential to confuse driver writers. Another possible approach you could take when the call to cancel_delayed_work fails (which should be rare) is to turn on RPM_WAKE in addition to RPM_IDLE and leave the suspend request queued. When __pm_runtime_suspend sees both flags are set, it should abort and set the status directly back to RPM_ACTIVE. At that time the idle notifications can start up again. Is this any better? I can't see how drivers would care, though. Alan Stern P.S.: What do you think should happen if there's a delayed suspend request pending, then pm_request_resume is called (and it leaves the request queued), and then someone calls pm_runtime_suspend? You've got two pending requests and a synchronous call all active at the same time! _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
