On Saturday, July 04, 2015 10:37:55 AM Alan Stern wrote: > On Sat, 4 Jul 2015, Rafael J. Wysocki wrote: > > > > >> > Perhaps the pm_runtime_suspended_if_enabled() test should be changed > > > >> > to > > > >> > pm_runtime_status_suspended(). Then it won't matter whether the > > > >> > descendant devices are enabled for runtime PM. > > > >> > > > >> Yeah, that would remove the need for messing with the runtime PM > > > >> enable status of descendant devices, but I wonder why Rafael went that > > > >> way initially. > > > > > > > > I forget the details. Probably it was just to be safe. We probably > > > > thought that if a device was disabled for runtime PM then its runtime > > > > PM status might not be accurate. But if direct_complete is set then it > > > > may be reasonable to assume that the runtime PM status _is_ accurate. > > > > > > Cool. > > > > We're walking a grey area here. What exactly does power.direct_complete > > mean > > for devices whose runtime PM is disabled? > > > > Let's see what Rafael thinks about these two issues. It seems to me > > > that the hardest part is dealing with drivers/subsystems that have no > > > runtime PM support. In such cases, we have to be very careful not to > > > use direct_complete unless we know that the device does no power > > > management at all. > > > > Precisely. > > All right, we can make a decision and document it. The following seems > reasonable to me: > > If dev->power.direct_complete is set then the PM core will > assume that dev->power.rpm_status is accurate even when > dev->power.disable_depth > 0. The core will obey the > .direct_complete setting regardless of .disable_depth. > > As a consequence, devices that support system sleep but don't > support runtime PM must _never_ have .direct_complete set. > > On the other hand, if a device (such as a "virtual" device) > requires no callbacks for either system sleep or runtime PM, > then there is no harm in setting .direct_complete. Indeed, > doing so may help speed up an ancestor device's sleep > transition. > > How does that sound?
It would be workable I think, but I'd prefer the core to be told directly about devices whose runtime PM status doesn't matter (because nothing changes between "suspended" and "active"), so they may be treated in a special way safely. If we had that information, no special rules other than "that is a device whose runtime PM status doesn't matter, so treat it accordingly" would be necessary. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
