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

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

On 07/15/2014 02:56 AM, 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.

If you only pass the following 2 cmdline options:
acpi_osi="!Windows 2012" video.brightness_switch_enabled=1
Will there be the /sys/class/backlight/acpi_videoX file?

Thanks,
Aaron