From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Matthew Garrett <matthew.garrett@nebula.com>, daniel.vetter@ffwll.ch
Cc: linux-acpi@vger.kernel.org, seth.forshee@canonical.com,
        joeyli.kernel@gmail.com, intel-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        lenb@kernel.org
Subject: Re: [PATCH 3/3] i915: Don't provide ACPI backlight interface if firmware expects Windows 8
Date: Fri, 05 Jul 2013 22:00:55 +0200
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On Friday, July 05, 2013 02:20:14 PM Rafael J. Wysocki wrote:
> On Sunday, June 09, 2013 07:01:39 PM Matthew Garrett 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@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))
> > 
> 
> Well, this causes build failures to happen when the ACPI video driver is
> modular and the graphics driver is not.
> 
> I'm not sure how to resolve that, so suggestions are welcome.

Actually, that happened with the radeon patch.

That said, ACPI_OSI_WIN_8 doesn't make much sense for !CONFIG_ACPI, for
example.

What about making acpi_video_register() do the quirk instead?  We could add an
argument to it indicating whether or not quirks should be applied.

Thanks,
Rafael


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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