On Tuesday, June 21, 2011, Alan Stern wrote: > On Mon, 20 Jun 2011, Rafael J. Wysocki wrote: > > > > Ah, okay. The PCI part makes sense then. > > > > OK, so the appended patch is a modification of the $subject one using > > pm_runtime_put_sync() instead of pm_runtime_put_noidle(). > > Yes, it looks good. Cool, thanks! > > So, your point is that while .suspend() or .resume() are running, the > > synchronization between runtime PM and system suspend/resume should be the > > subsystem's problem, right? > > Almost but not quite. I was talking about the time period between > .prepare() and .suspend() (and also the time period between .resume() > and .complete()). > > It's probably okay to prevent pm_runtime_suspend() from working during > .suspend() or .resume(), but it's not a good idea to prevent > pm_runtime_resume() from working then. OK, but taking a reference by means of pm_runtime_get_noresume() won't block pm_runtime_resume(). > > I actually see a reason for doing this. Namely, I don't really think > > driver writers should be bothered with preventing races between different > > PM callbacks from happening. Runtime PM takes care of that at run time, > > the design of the system suspend/resume code ensures that the callbacks > > for the same device are executed sequentially, but if we allow runtime PM > > callbacks to be executed in parallel with system suspend/resume callbacks, > > someone has to prevent those callbacks from racing with each other. > > > > Now, if you agree that that shouldn't be a driver's task, then it has to > > be the subsystem's one and I'm not sure what a subsystem can do other than > > disabling runtime PM or at least taking a reference on every device before > > calling device drivers' .suspend() callbacks. > > > > Please note, I think that .prepare() and .complete() are somewhat special, > > so perhaps we should allow those to race with runtime PM callbacks, but IMO > > allowing .suspend() and .resume() to race with .runtime_suspend() and > > .runtime_resume() is not a good idea. > > Races in the period after .suspend() and before .resume() will be > handled by disabling runtime PM when .suspend() returns and enabling it > before calling .resume(). OK > During the .suspend and .resume callbacks, races with > .runtime_suspend() can be prevented by calling > pm_runtime_get_noresume() just before .suspend() and then calling > pm_runtime_put_sync() just after .resume(). So, you seem to suggest to call pm_runtime_get_noresume() in __device_suspend() and pm_runtime_put_sync() in device_resume(). That would be fine by me, perhaps up to the "sync" part of the "put". > Races with .runtime_resume() can be handled to some extent by putting a > runtime barrier immediately after the pm_runtime_get_noresume() call, > but that's not a perfect solution. Is it good enough? It's not worse than what we had before, so I guess it should be enough. > > > What I'm suggesting is to revert the commit but at the same time, > > > move the get_noresume() into __device_suspend() and the put_sync() into > > > device_resume(). > > > > What about doing pm_runtime_get_noresume() and the pm_runtime_barrier() > > in dpm_prepare(), but _after_ calling device_prepare() and doing > > pm_runtime_put_noidle() in dpm_complete() _before_ calling .complete() > > from the subsystem > > This does not address the issue of allowing runtime suspends in the > windows between .prepare() - .suspend() and .resume() - .complete(). OK > > (a _put_sync() at this point will likely invoke > > .runtime_idle() from the subsystem before executing .complete(), which may > > not be desirable)? > > It should be allowed. The purpose of .complete() is not to re-enable > runtime power management of the device; it is to release resources > (like memory) allocated during .prepare() and perhaps also to allow new > children to be registered under the device. Right. But does "allowed" mean the core _should_ do it at this point? We may as well call pm_runtime_idle() directly from rpm_complete(), but perhaps it's better to call it from device_resume(), so that it runs in parallel for async devices. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
