On Tuesday 30 June 2009, Alan Stern wrote: > On Mon, 29 Jun 2009, Rafael J. Wysocki wrote: > > > > 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. > > What other purpose? We don't send idle notifications in RPM_IDLE OK > and resume requests don't need to be stored since (as described above) they > just set the RPM_WAKE flag. Hence nothing else needs to use the > work_struct. Good. I'd go for it, then. OK? > > 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. > > You seem to be thinking about these requests in a very different way > from me. They don't form a queue or anything like that. Instead they > mean "Change the device's power state to this value as soon as > possible" -- and they are needed only because sometimes (in atomic or > interrupt contexts) the change can't be made right away. > > That's why it doesn't make any sense to have both a suspend and a > resume request pending at the same time. It would mean the driver is > telling us "Change the device's power state to both low-power and > full-power as soon as possible"! > > We should settle on a general policy for how to handle it when a > driver makes the mistake of telling us to do contradictory things. > There are three natural policies: > > The first request takes precedence over the second; > > The second request takes precedence over the first; > > Resumes take precedence over suspends. > > Any one of those would be acceptable. IMO resumes should take precedence over suspends, because resume usually means "there's I/O to process" and we usually we want the I/O to be processed as soon as possible (deferred wake-up will usually mean deferred I/O and that would hurt user experience). 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
