[PATCH 3/3] i915: Don't provide ACPI backlight interface if firmware expects Windows 8

[Alex Deucher]

Radeon probably needs something similar.  See attached untested patch.

Alex

On Sun, Jun 9, 2013 at 7:01 PM, Matthew Garrett
<matthew.garrett at nebula.com> wrote:
> 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 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.
>
> Signed-off-by: Matthew Garrett <matthew.garrett at nebula.com>
> ---
>  drivers/gpu/drm/i915/i915_dma.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
> index 3b315ba..23b6292 100644
> --- a/drivers/gpu/drm/i915/i915_dma.c
> +++ b/drivers/gpu/drm/i915/i915_dma.c
> @@ -1661,6 +1661,9 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
>                 /* Must be done after probing outputs */
>                 intel_opregion_init(dev);
>                 acpi_video_register();
> +               /* Don't use ACPI backlight functions on Windows 8 platforms */
> +               if (acpi_osi_version() >= ACPI_OSI_WIN_8)
> +                       acpi_video_backlight_unregister();
>         }
>
>         if (IS_GEN5(dev))
> --
> 1.8.2.1
>
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