From mboxrd@z Thu Jan  1 00:00:00 1970
From: Aaron Lu <aaron.lu@intel.com>
Subject: Re: [PATCH v3 3/4] ACPI / video: Do not register backlight if win8
 and native interface exists
Date: Thu, 26 Sep 2013 13:15:53 +0800
Message-ID: <20130926051552.GB14158@aaronlu.linux.com>
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To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: linux-acpi@vger.kernel.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Daniel Vetter <daniel@ffwll.ch>, Matthew Garrett <matthew.garrett@nebula.com>, Seth Forshee <seth.forshee@canonical.com>, Lee Chun-Yi <joeyli.kernel@gmail.com>, Richard Purdie <rpurdie@rpsys.net>, Igor Gnatenko <i.gnatenko.brain@gmail.com>, Yves-Alexis Perez <corsac@debian.org>, Felipe Contreras <felipe.contreras@gmail.com>, Henrique de Moraes Holschuh <ibm-acpi@hmh.eng.br>, Jani Nikula <jani.nikula@linux.intel.com>, Ben Jencks <ben@bjencks.net>, Steven Newbury <steve@snewbury.org.uk>, James Hogan <james@albanarts.com>, Kamal Mostafa <kamal@canonical.com>, Joerg Platte <jplatte@naasa.net>, Kalle Valo <kvalo@adurom.com>, Martin Steigerwald <Martin@lichtvoll.de>, =?iso-8859-1?Q?J=F6rg?= Otte <jrg.otte@gmail.com>, Mike Galbraith <bitbucket@onlin>
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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