linux-kernel - Re: [PATCH v3 3/4] ACPI / video: Do not register backlight if win8 and native interface exists

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Message-ID: <20130926051552.GB14158@aaronlu.linux.com>
Date:	Thu, 26 Sep 2013 13:15:53 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-acpi@...r.kernel.org, intel-gfx@...ts.freedesktop.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Daniel Vetter <daniel@...ll.ch>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	Seth Forshee <seth.forshee@...onical.com>,
	Lee Chun-Yi <joeyli.kernel@...il.com>,
	Richard Purdie <rpurdie@...ys.net>,
	Igor Gnatenko <i.gnatenko.brain@...il.com>,
	Yves-Alexis Perez <corsac@...ian.org>,
	Felipe Contreras <felipe.contreras@...il.com>,
	Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	Ben Jencks <ben@...ncks.net>,
	Steven Newbury <steve@...wbury.org.uk>,
	James Hogan <james@...anarts.com>,
	Kamal Mostafa <kamal@...onical.com>,
	Joerg Platte <jplatte@...sa.net>,
	Kalle Valo <kvalo@...rom.com>,
	Martin Steigerwald <Martin@...htvoll.de>,
	Jörg Otte <jrg.otte@...il.com>,
	Mike Galbraith <bitbucket@...ine.de>
Subject: Re: [PATCH v3 3/4] ACPI / video: Do not register backlight if win8
 and native interface exists

On Wed, Sep 25, 2013 at 07:53:13PM +0200, Rafael J. Wysocki wrote:
> On Tuesday, September 24, 2013 05:47:31 PM Aaron Lu wrote:
> > According to Matthew Garrett, "Windows 8 leaves backlight control up
> > to individual graphics drivers rather than making ACPI calls itself.
> > There's plenty of evidence to suggest that the Intel driver for
> > Windows [8] doesn't use the ACPI interface, including the fact that
> > it's broken on a bunch of machines when the OS claims to support
> > Windows 8.  The simplest thing to do appears to be to disable the
> > ACPI backlight interface on these systems".
> > 
> > So for Win8 systems, if there is native backlight control interface
> > registered by GPU driver, ACPI video will not register its own. For
> > users who prefer to keep ACPI video's backlight interface, the existing
> > kernel cmdline option acpi_backlight=video can be used.
> 
> I think the idea is to use the aggressive default for now and we can switch the
> default back to the current behavior before the merge window in case there are
> too many problems with it?

Yes I think so.

Thanks,
Aaron
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