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

[Aaron Lu <aaron.lu@intel.com>]

On 07/15/2014 08:27 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?
> 
> It seems that it may break other systems without a desktop environment, may it not?

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

Thanks,
Aaron