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SubjectRe: [BUGFIX] PM: Fix active child counting when disabled and forbidden
On Wed, 7 Nov 2012, Rafael J. Wysocki wrote:

> On Wednesday, November 07, 2012 12:17:02 PM Alan Stern wrote:
> > On Wed, 7 Nov 2012, Rafael J. Wysocki wrote:
> >
> > > > The PCI subsystem assumes that
> > > > driverless devices are not in use, so they are disabled for runtime PM
> > > > and marked as suspended. This is not appropriate for VGA devices,
> > > > which can indeed be used without a driver.
> > > >
> > > > I'm not sure what the best solution is. Maybe we should Ying's
> > > > proposal a step farther:
> > > >
> > > > Make pm_runtime_set_suspended() fail if runtime PM is
> > > > forbidden.
> > > >
> > > > Make pm_runtime_forbid() call pm_runtime_set_active()
> > > > (and do a runtime resume of the parent) if disable_depth > 0.
> > >
> > > I'd prefer this one.
> >
> > That wasn't meant to be a choice. The first item is close to what the
> > original patch did; I was suggesting that we should adopt all three
> > items.
>
> OK, I need to think about this a bit more, then.
>
> The problem seems to be that our initial assumption, ie. that driverless
> devices won't be in use, is not satisfied in the relevant case. It may
> not be satisfied in more cases like this, I suppose, but so far we don't
> really know.

Right. The reasoning behind my proposal goes like this: When there's
no driver, the subsystem can let userspace directly control the
device's power level through the power/control attribute.

Alan Stern



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