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SubjectRe: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended.
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On Tuesday, June 17, 2014 10:11:32 AM Alan Stern wrote:
> On Mon, 16 Jun 2014, Rafael J. Wysocki wrote:
>
> > > For reasons having nothing to do with Allen's suggested change, I
> > > wonder if we shouldn't replace this line with something like:
> > >
> > > - else if (dev->power.disable_depth == 1 && dev->power.is_suspended
> > > + else if (dev->power.disable > 0 && !dev->power.is_suspended
> > > && dev->power.runtime_status == RPM_ACTIVE)
> > > retval = 1;
> > >
> > > It seems that I've been bitten by this several times in the past.
> > > When a device is disabled for runtime PM, and more or less permanently
> > > stuck in the RPM_ACTIVE state, calls to pm_runtime_resume() or
> > > pm_runtime_get_sync() shouldn't fail.
> > >
> > > For example, suppose some devices of a certain type support runtime
> > > power management but others don't. We naturally want to call
> > > pm_runtime_disable() for the ones that don't. But we also want the
> > > same driver to work for all the devices, which means that
> > > pm_runtime_get_sync() should return success -- otherwise the driver
> > > will think that something has gone wrong.
> > >
> > > Rafael, what do you think?
> >
> > That condition is there specifically to take care of the system suspend
> > code path. It means that if runtime PM is disabled, but it only has been
> > disabled by the system suspend code path, we should treat the device as
> > "active" (ie. return 1). That won't work after the proposed change.
>
> Ah, yes, quite true. Okay, suppose we replace that line with just:
>
> + else if (dev->power.disable > 0
>
> > I guess drivers that want to work with devices where runtime PM may be
> > disabled can just check the return value of rpm_resume() for -EACCES?
>
> They could, but it's extra work and it's extremely easy to forget
> about. I'd prefer not to do things that way.

In that case we need to audit all code that checks the return value of
__pm_runtime_resume() to verify that it doesn't depend on the current
behavior in any way. It shouldn't, but still.

Also we probably should drop the -EACCES return value from rpm_resume() in the
same patch, because it specifically only covers the dev->power.disable > 0 case
(which BTW is consistent with the suspend side of things, so I'm totally unsure
about that being the right thing to do to be honest).

Rafael



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