linux-kernel - Re: [PATCH v2 3/3] ACPI / video: Do not register backlight if win8 and native interface exists

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Date:	Fri, 20 Sep 2013 15:02:12 +0200
From:	Yves-Alexis Perez <corsac@...ian.org>
To:	Aaron Lu <aaron.lu@...el.com>
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>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	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>,
	Felipe Contreras <felipe.contreras@...il.com>,
	Henrique de Moraes Holschuh <ibm-acpi@....eng.br>,
	Jani Nikula <jani.nikula@...ux.intel.com>
Subject: Re: [PATCH v2 3/3] ACPI / video: Do not register backlight if win8
 and native interface exists

On mar., 2013-09-17 at 17:23 +0800, 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.
> 
> This patch is an evolution from previous work done by Matthew Garrett,
> Chun-Yi Lee, Seth Forshee and Rafael J. Wysocki.
> 
> Signed-off-by: Aaron Lu <aaron.lu@...el.com>
Tested-by: Yves-Alexis Perez <corsac@...ian.org>
-- 
Yves-Alexis

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