Messages in this thread | | | Date | Sat, 4 Jul 2015 10:37:55 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive |
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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?
Alan Stern
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