linux-kernel - Re: [BUGFIX] PM: Fix active child counting when disabled and forbidden

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Date:	Wed, 07 Nov 2012 21:21:25 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Huang Ying <ying.huang@...el.com>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [BUGFIX] PM: Fix active child counting when disabled and forbidden

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.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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