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

[Igor Gnatenko]

On Tue, 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 at intel.com>
Tested-by: Igor Gnatenko <i.gnatenko.brain at gmail.com>
> ---
>  drivers/acpi/internal.h     |  5 ++---
>  drivers/acpi/video.c        | 27 +++++----------------------
>  drivers/acpi/video_detect.c | 14 ++++++++++++--
>  3 files changed, 19 insertions(+), 27 deletions(-)

-- 
Igor Gnatenko
Fedora release 20 (Heisenbug)
Linux 3.12.0-0.rc1.git0.1.fc20.x86_64