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

[Aaron Lu]

On 07/31/2013 08:01 AM, 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?

Sounds good to me.

-Aaron
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