On Thursday, January 27, 2011, Alan Stern wrote: > 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. That requirement is long gone, because timer interrupts are still enabled when the _noirq() callbacks are run. The _noirq part means that the driver's own interrupt handler is guaranteed not to run concurrently with the routines (unless this also is a timer interrupt, that is). Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
