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

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

On 07/16/2014 02:29 PM, Hans de Goede wrote:
> Hi,
> 
> On 07/16/2014 02:43 AM, Rafael J. Wysocki wrote:
>> On Tuesday, July 15, 2014 10:45:29 PM Aaron Lu wrote:
>>> On 07/15/2014 10:05 PM, Hans de Goede wrote:
>>
>> [cut]
>>
>>>> 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.
>>>
>>> Right.
>>> So this condition should be:
>>> 1 ACPI backlight interface works in Win8 mode;
>>>
>>> This means, for Julian's system, the commit 751109aad583 doesn't need to
>>> be reverted as the ACPI backlight interface on his system only works
>>> when the acpi_osi="!Windows 2012" is added. In that case, the
>>> video.use_native_backlight=X doesn't make any difference anymore.
>>
>> But Julian reports that he needs to revert that commit to make things work
>> as before for him.  What gives?
> 
> Likely what is happening is that this commit is still affecting Julian because
> we check if the bios is advertising win8 support, not if we are advertising win8
> support ourselves.

Perhaps the firmware on Julian's laptop has _OSI("Windows 2013") and if that
is the case, the acpi_gbl_osi_data will still get the value of ACPI_OSI_WIN_8
and acpi_osi_is_win8() will return true...

Julian,
Please attach your acpidump, thanks.

> 
> Julian, I've jumped into this thread halfway, so I'm not 100% clear on your
> original problem. From what I've read sofar you need acpi_osi="!Windows 2012"
> for backlight control to work. That in itself is a sign that things are not
> as they should be, and this is actually what the new default of
> video.use_native_backlight=1 is trying to fix.
> 
> If you boot the new kernel without acpi_osi="!Windows 2012" and without
> video.use_native_backlight=X (so using the new default of
> video.use_native_backlight=1), what does ls /sys/class/backlight say then ?
> 
> If there is a directory in there can you then cd in to that directory,
> and do: "cat max_brightness" and then "echo value > brightness" (the latter
> as root) with value being a number, once half of max_brightness, once
> full brightness and see if this controls your backlight brightness.
> 
> Assuming this test succeeds, is your problem resolved then? And if not
> what is the problem?

The problem is Julian is using a lightweight GUI that do not respond to
backlight hotkey events. So he needs the in kernel processing of
backlight events and for that to work, he has to add the
acpi_osi="!Windows 2012" cmdline option.

-Aaron