ACPI / video: Do not register backlight if win8 and native interface exists
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 does not need to register its own. Since there are systems that don't work well with this approach, a parameter for video module named use_native_backlight is introduced and has the value of false by default. For users who have a broken ACPI video backlight interface, video.use_native_backlight=1 is needed in kernel cmdline. Signed-off-by:Aaron Lu <aaron.lu@intel.com> Signed-off-by:
Rafael J. Wysocki <rafael.j.wysocki@intel.com>
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