[Update][PATCH 0/3] Fix backlight issues on some Windows 8 systems

[Igor Gnatenko]

On Wed, 2013-07-31 at 02:01 +0200, Rafael J. Wysocki wrote:
> On Thursday, July 18, 2013 02:16:09 AM Rafael J. Wysocki wrote:
> > On Sunday, June 09, 2013 07:01:36 PM Matthew Garrett wrote:
> > > Windows 8 introduced new policy for backlight control by pushing it out to
> > > graphics drivers. This appears to have coincided with a range of vendors
> > > adding Windows 8 checks to their backlight control code which trigger either
> > > awkward behaviour (Lenovo) or complete brokenness (some Dells). The simplest
> > > thing to do would be to just disable ACPI backlight control entirely if the
> > > firmware indicates Windows 8 support, but it's entirely possible that
> > > individual graphics drivers might still make use of the ACPI functionality in
> > > preference to native control.
> > > 
> > > The first two patches in this series are picked from other patchesets aimed at
> > > solving similar problems. The last simply unregisters ACPI backlight control
> > > on Windows 8 systems when using an Intel GPU. Similar code could be added to
> > > other drivers, but I'm reluctant to do so without further investigation as
> > > to the behaviour of the vendor drivers under Windows.
> > 
> > Well, after some more time spent on that, we now have a series of 3 patches
> > (different from the $subject one) that we think may be used to address this
> > issue.  As far as I can say, it has been tested by multiple people whose
> > systems have those problems and they generally saw improvement.
> > 
> > It is not my ideal approach, but it seems to be the least intrusive and/or
> > with the least amount of possible side effects that we can do right now
> > as a general measure (alternatively, we could create a possibly long
> > blacklist table of affected systems with different workarounds for them,
> > but let's just say that is not overwhelmingly attractive).
> > 
> > [1/3] Make ACPICA export things that we need for checking OSI(Win8).
> > 
> > [2/3] Make acpi_video_device_find_cap() call acpi_video_init_brightness() even
> >       if it is not going to register the backlight interface (needed for
> >       Thinkpads).
> > 
> > [3/3] Avoid using ACPI backlight if i915 is in use and the firmware believes
> >       we are Windows 8.
> > 
> > Many thanks to everyone involved!
> 
> So this didn't work, as we had to revert [3/3], but I think we should try to
> make some progress with this nevertheless.  A way forward I'm seeing now could
> be to
> (1) Split the ACPI video driver so that it is possible to register the
>     backlight control separately from the event interface.
> (2) Add a command line option to i915 to make it use the native backlight
>     control (without registering the ACPI one) if set.  Make unset the
>     default initially.
> (3) Fix i915 backlight control issues for all systems known to have them
>     (that may take a while) and flip the defailt for that option to set when we
>     think we're ready.
> (4) If there still are problem reports, flip the default back to unset and
>     repeat (3).
> 
> If this converges, everyone will be using the native backlight control by
> default and the original problem will go away automatically.
> 
> Thoughts?
> 
> Rafael
> 
> 
Good idea. I have 3-4 laptops with this problem. I can test, but I don't
have devices, on which found regressions (in backlight) in previous
patch.
-- 
Igor Gnatenko
Fedora release 19 (Schrödinger’s Cat)
Linux 3.10.3-300.fc19.x86_64