Re: [Regression]: Changing brightness does not work with v3.16-rc4

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 07/15/2014 02:27 PM, Rafael J. Wysocki wrote:
> On Tuesday, July 15, 2014 02:06:21 PM Aaron Lu wrote:
>> On 07/15/2014 03:17 AM, Rafael J. Wysocki wrote:
>>> On Monday, July 14, 2014 08:56:29 PM Julian Wollrath wrote:
>>>> Am Mon, 14 Jul 2014 21:10:47 +0200
>>>> schrieb "Rafael J. Wysocki" <rjw@rjwysocki.net>:
>>>>
>>>>> On Monday, July 14, 2014 09:02:34 PM Rafael J. Wysocki wrote:
>>>>>> On Monday, July 14, 2014 08:34:22 PM Julian Wollrath wrote:
>>>>>>> Am Mon, 14 Jul 2014 20:21:19 +0200
>>>>>>> schrieb "Rafael J. Wysocki" <rjw@rjwysocki.net>:
>>>>>>>
>>>>>>>> On Saturday, July 12, 2014 06:24:52 PM Julian Wollrath wrote:
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>>> changing the brightness on my Thinkpad X230 with Intel
>>>>>>>>>> HD4000 graphics, stopped working after commit 886129a8eebe
>>>>>>>>>> (ACPI / video: change acpi-video brightness_switch_enabled
>>>>>>>>>> default to 0). Changing it back to 1, fixes the problem, if
>>>>>>>>>> "acpi_osi=!Windows 2012" is also set. Before that commit
>>>>>>>>>> just setting "acpi_osi=!Windows 2012" was enough to get
>>>>>>>>>> changing the brightness working.
>>>>>>>>>
>>>>>>>>> small correction: It setting "acpi_osi=!Windows 2012" does
>>>>>>>>> only help when using a kernel with commit 886129a8eebe as
>>>>>>>>> HEAD, with v3.16-rc4 setting
>>>>>>>>> video.brightness_switch_enabled=1 and acpi_osi=!Windows 2012
>>>>>>>>> or just one of them, does not make changing the brightness
>>>>>>>>> work again.
>>>>>>>>
>>>>>>>> And reverting commit 751109aad583 (ACPI / video: Change the
>>>>>>>> default for video.use_native_backlight to 1) make that last
>>>>>>>> problem go away, right?
>>>>>>>>
>>>>>>>> We are going to rever commit 886129a8eebe for other reasons, so
>>>>>>>> can you please revert it from 3.16-rc5 on your system and
>>>>>>>> report back?
>>>>>>> Yes, with both 751109aad583 and 886129a8eebe reverted, changing
>>>>>>> the brightness works again.
>>>>>>
>>>>>> What if you revert 886129a8eebe alone?
>>>>>
>>>>> I mean, what exactly do you need to pass to the kernel command line
>>>>> in that case to make brightness switching work?
>>>> I need to pass
>>>>    acpi_osi="!Windows 2012" video.brightness_switch_enabled=1 video.use_native_backlight=-1
>>>>
>>>> If I leave one of these parameters out, the brightness switch stops
>>>> working.
>>>
>>> With 886129a8eebe reverted you should not need video.brightness_switch_enabled=1.
>>>
>>> Aaron, what do you think?
>>
>> I agree.
>>
>> I suppose Julian is not using an standard GUI so he needs the in kernel
>> processing of the backlight event. And his laptop has a broken ACPI
>> interface in Win8 mode, so he also needs the "!Windows 2012" option.
>>
>> With a standard GUI environment, his system would have only one
>> interface left: the GPU one and everything should work. But of course,
>> that may not be his config.
>
> Well, do we need to revert 751109aad583 too, then?

No, just no, clearly using the acpi video interface for backlight control
is the wrong thing to do on win8 generation laptops, if we don't flip
the default we're going to end up with a never ending list of quirks
for models where the acpi-video interface is broken.

On 07/15/2014 04:00 PM, Aaron Lu wrote:

 > If we have to consider the following config:
 > 1 ACPI backlight interface works(or can work with some cmdline option);

And the BIOS advertises native win8 support.

 > 2 Not using a normal GUI(depends on ACPI video module to do the in
 >    kernel backlight level change on hotkey press).
 > Then we will need to revert 751109aad583.

I think the combination of 1 and 2 makes the subset of users
potentially affected by this so small, that we really should
continue with video.use_native_backlight=1 as default, the
other route adding more and more and more and more quirks
is sheer madness.

Regards,

Hans