linux-kernel - Re: [PATCH] PM / i915: Skip kernel VT switch during suspend/resume if KMS is used

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Message-ID: <20100126141726.GA1437@ucw.cz>
Date:	Tue, 26 Jan 2010 15:17:27 +0100
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Len Brown <lenb@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	dri-devel@...ts.sourceforge.net, Eric Anholt <eric@...olt.net>,
	airlied@...ux.ie
Subject: Re: [PATCH] PM / i915: Skip kernel VT switch during suspend/resume
	if KMS is used

On Mon 2010-01-25 22:54:37, Rafael J. Wysocki wrote:
> On Monday 25 January 2010, Alan Cox wrote:
> > > > But in that case we should be able to disable the VT switch disable
> > > > path; we just have to check each driver as it's loaded.
> > > 
> > > OK, what the right sequence of checks would be in that case and where to place
> > > them?
> > 
> > Why are we even driving a vt switch direct from the suspend/resume
> > logic ? The problem starts there. If it was being handled off the device
> > suspend/resume method then there wouldn't be a mess to start with ?
> > 
> > Start at the beginning
> > 
> > - Why do we switch to arbitarily chosen 'last vt'
> > - Why isn't vt related suspend/resume handled by the device
> 
> Well, that was added long ago as a workaround for some problems people
> reported (presumably).  I've never looked at that before, so I can't really
> tell why someone did it this particular way.

As X drives hardware, it is/was neccessary to get control out of X and
console switch was convenient.

Note that it needs to happen with userland still active -- before
freezer.

And yes, it should be per-driver these days.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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