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

Aaron Lu aaron.lu at intel.com
Wed Sep 25 22:15:53 PDT 2013

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.


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