On Monday 29 June 2009, Alan Stern wrote: > 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. There still is the problem that the suspend request is occupying the work_struct which cannot be used for any other purpose. I don't think this is avoidable, though. This way or another it is possible to have two requests pending at a time. Perhaps the simplest thing to do would be to simply ignore pending suspend requests in both pm_request_resume() and pm_runtime_resume() and to allow them to be scheduled at any time. That shouldn't hurt anything as long as pm_runtime_suspend() is smart enough, but it has to be anyway, because it can be run synchronously at any time. The only question is what pm_runtime_suspend() should do when it sees a pending suspend request and quite frankly I think it can just ignore it as well, leaving the RPM_IDLE bit set. In which case the name RPM_IDLE will not really be adequate, so perhaps it can be renamed to RPM_REQUEST or something like this. Then, we'll need a separate work structure for suspend requests, but I have no problem with that. > 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! That's easy, pm_runtime_suspend() sees a pending resume, so it quits and the other things work out as usual. 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
