On Wednesday 24 June 2009, Alan Stern wrote: > On Wed, 24 Jun 2009, Rafael J. Wysocki wrote: > > > > One question still remains: If the counter is 0 at the end of a > > > successful pm_runtime_resume, should the core then call pm_notify_idle? > > > Or should we make the driver responsible for that too? > > > > Good question. :-) > > > > I think the core may call pm_notify_idle() in that case, but not necessarily in > > the synchronous case. > > I'm not sure; we may want to do it even for synchronous resumes. > Otherwise the callers would be forced to do it. I have no strong opinion. We can do it in the sychronous case too. > There's also the other side of the coin. What if the counter is 0 at > the end of a failed pm_runtime_suspend? > > For example, suppose the driver's runtime_suspend method decides that > the device hasn't been idle for long enough, so it wants to fail the > suspend attempt with -EBUSY and queue a new delayed autosuspend > request. But at this point the status is RPM_SUSPENDING, so new > suspend requests won't be accepted (N.B., the test for this in the most > recent patch doesn't look right). In fact it was inversed (fixed now), thanks for spotting this! > Even with a queued notification, there's no guarantee that the > notification won't be sent before the status changes from > RPM_SUSPENDING to RPM_ACTIVE. So we really do need the notification to > be sent by pm_runtime_suspend, after it has updated the status and > dropped the lock. OK > There's another totally separate issue worth discussing here. This > will affect the USB implementation of the new runtime PM framework. > > The difficulty is that some USB interface drivers require remote wakeup > to be enabled while their interfaces are suspended. But remote wakeup > is a global setting; it doesn't take effect until the entire physical > device is suspended. (To put it another way, USB has no notion of > suspending interfaces.) This means we must not allow these interfaces > to be suspended before the whole device is. But the whole device is > the parent of the interfaces -- if we can't suspend the children before > suspending the parent then we're stuck. Not if we use the power.ignore_children flag on the parent. > Clearly this is something the USB stack has to deal with; it shouldn't > affect the general PM framework. However the only solution I can think > of involves subverting the framework, which isn't very nice. The idea > is to ignore runtime_suspend callbacks for these interface drivers; > allow them to keep on running even though the PM core thinks they are > suspended. Then suspend and resume them as part of the callbacks for > the entire device. (For interface drivers that don't require remote > wakeup there is no problem; it doesn't matter when they get suspended.) > > This will work, but it's a hack. Does anybody have a better idea? Well, as I said above, you can set power.ignore_children on the device and then it can be suspended even if the interfaces aren't. 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
