On Wed, 26 Jan 2011, Kevin Hilman wrote: > >> Consider this instead: Since A is required to be functional before B > >> can be used, A must be registered before B and hence B gets suspended > >> before A. Therefore during the prepare phase we can runtime-resume A > >> and leave it powered up; when B needs to suspend, it won't matter that > >> the runtime-PM calls are ineffective. > > > > We don't really need to do that, because the runtime resume _is_ functional > > during system suspend. Not asynchronous runtime resume, because the workqueue is frozen. But that's not the issue here. > > The only thing missing is a ->suspend() callback for A > > (and a corresponding ->resume() callback to make sure A will be available to > > B during system resume). > > > > OK, I'm finally back to debugging this problem and looking for a final > solution. > > I agree that what is needed is ->suspend() and ->resume() callbacks for > A, but the question remains how to implement them. > > In my case, A doesn't need runtime callbacks, but *does* require that > the subsystem callbacks are called because the subsystem actually does > all the real PM work. On OMAP, the device PM code (clock mgmt, device > low-power states, etc.) is common for all on-chip devices, so is handled > in common code at the subsystem level (in this case, platform_bus.) > > Therefore, what is ideally needed is the ability for A's suspend to > simply call pm_runtime_suspend() so the subsystem can do the work. > However, since runtime transitions are locked out by this time, that > doesn't work. IOW, what is needed is a way for a system suspend to say > "please finish the runtime suspend that was already requested." Calling the runtime_suspend method directly is the way to do it. > What I've done to work around this in driver A is to manually check > pm_runtime_suspended() and directly call the subsystem's runtime > suspend/resume (patch below[1]. NOTE, I've used the _noirq methods to > ensure device A is available when device B needs it.) Hmm. The pm_runtime_suspended() check may not be needed (if A were suspended already then B would have encountered problems). But including it doesn't hurt. Using the _noirq method isn't a good idea, unless you know for certain that the runtime_suspend handler doesn't need to sleep. Using the normal suspend method should work okay, because B always has to suspend before A. > While this works, I'm not crazy about it since it requires the driver > know about the subsystem (in this case the bus) where the real PM work > is done. IMO, it would be much more intuitive (and readable) if the > driver's suspend hooks could simply trigger a runtime suspend (either a > new one, or one already requested.) This isn't clear to me. Isn't the driver registered on the bus in question? Can't the driver therefore call the bus's runtime_suspend routine directly, instead of dereferencing the bus->pm->runtime_suspend pointer? Alan Stern _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
