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SubjectRe: [PATCH v3 2/2] PM / Runtime: Add pm_runtime_enable_recursive
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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