On Monday 29 June 2009, Alan Stern wrote: > On Mon, 29 Jun 2009, Rafael J. Wysocki wrote: > > > > > So, it seems, pm_request_resume() can't kill suspend requests by itself > > > > and instead it has to queue up resume requests for this purpose, which > > > > brings us right back to the problem of two requests queued up at a time > > > > (a delayed suspend request and a resume request that is supposed to cancel it). > > > > > > No, you're trying to do too much. If the state is RPM_IDLE (i.e., a > > > suspend request is pending) then rpm_request_resume doesn't need to do > > > anything. The device is already resumed! Sure, it can try to kill the > > > request and change the state to RPM_ACTIVE, but it doesn't need to. > > > > I think it does need to do that, because the reuqest may be scheduled way > > in the future and we can't preserve its work structure until it runs. > > pm_request_resume() doesn't know in advance when the suspend work function is > > going to be queued up and run. > > It doesn't need to know. All it needs to do is guarantee that the > device will be in a resumed state some time not long after the function > returns. Thus calling rpm_request_resume while the status is RPM_IDLE > is like calling it while the status is RPM_ACTIVE. In neither case > does it have to do anything, because the device will already be resumed > when it returns. Not exactly, because RPM_IDLE prevents idle notifications from being run, as it means a suspend has already been requested, which is not really the case after pm_request_resume(). > Perhaps instead we should provide a way to kill a pending suspend > request? It's not clear that anyone would need this. The only reason > I can think of is if you wanted to change the timeout duration. But it > wouldn't be able to run in interrupt context. > > > > Think about it. Even if the suspend request were killed off, there's > > > always the possibility that someone could call rpm_runtime_suspend > > > right afterward. If the driver really wants to resume the device and > > > prevent it from suspending again, then the driver should call > > > pm_runtime_get before pm_request_resume. Then it won't matter if the > > > suspend request runs. > > > > No, it doesn't matter if the request runs, but it does matter if the work > > structure used for queuing it up may be used for another purpose. :-) > > What else would it be used for? If rpm_request_resume returns without > doing anything and leaves the status set to RPM_IDLE, then the work > structure won't be reused until the status changes. Which is not right, because we may want to run ->runtime_idle() before the status is changed. That's why I think pm_request_resume() should queue up a resume request if a suspend request is pending. > > The problem with pm_<something>_put is that it does two things at a time, > > decrements the resume counter and runs or queues up an idle notification. > > Perhaps it's a good idea to call it after the second thing and change > > pm_runtime_get() to pm_runtime_inuse(), so that we have: > > > > * pm_runtime_inuse() - increment the resume counter > > * pm_runtime_idle() - decrement the resume counter and run idle notification > > * pm_request_idle() - decrement the resume counter and queue idle notification > > > > and __pm_runtime_idle() as the "bare" idle notification function? > > I could live with that, but the nice thing about "get" and "put" is > that they directly suggest a counter is being maintained and therefore > the calls have to balance. Maybe we should just call it > rpm_request_put and not worry that the put happens immediately. OK Best, Rafael -- 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
