Re: Linux 3.11-rc2 [backlight] [ASUS N56VZ]

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 25 Jul 2013, "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> On Wednesday, July 24, 2013 02:05:15 PM Linus Torvalds wrote:
>> On Wed, Jul 24, 2013 at 2:02 PM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>> >
>> > I think a i915 module option should be doable, otoh people seem to have a
>> > viable workaround by setting a different acpi os version already.
>> 
>> At least the original claim was that if you set a non-windows8 acpi os
>> version, you hit other bugs..
>> 
>> But yeah, if we just do a plain revert, that may be the only option
>> for the people for whom the current (to-be-reverted) patches made
>> things work.
>
> Well, I wonder what about the appended (untested) patch?

Rafael, before going there, I've been trying to wrap my (poor, rusty
after vacation) head around

commit 8c5bd7adb2ce47e6aa39d17b2375f69b0c0aa255
Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Date:   Thu Jul 18 02:08:06 2013 +0200

    ACPI / video / i915: No ACPI backlight if firmware expects Windows 8

and I can't see how it could work.

First, the ACPI_VIDEO_SKIP_BACKLIGHT flag seems to be checked before
it's actually set anywhere. Buried deep in the calls from
acpi_video_bus_add(), acpi_video_verify_backlight_support() is used
before acpi_video_backlight_quirks() gets called. (Perhaps if i915 is
reloaded, this goes right as the flags are already set.)

Second, with i915 that has opregion support, __acpi_video_register()
should only ever get called once. Which means the acpi_walk_namespace()
with video_unregister_backlight() should never get called in register.

Please enlighten me.

BR,
Jani.

-- 
Jani Nikula, Intel Open Source Technology Center