[Intel-gfx] [REGRESSION BISECTED] backlight control stops workin with 3.14 and later

[Bertrik Sikken]

On 19-8-2014 3:29, Jani Nikula wrote:
> On Tue, 19 Aug 2014, Bertrik Sikken <bertrik at sikken.nl> wrote:
>>> On Sun, 17 Aug 2014, Bertrik Sikken <bertrik at sikken.nl> wrote:
>>>> On 15-8-2014 3:43, Jani Nikula wrote:
>>>>> On Thu, 14 Aug 2014, Bertrik Sikken <bertrik at sikken.nl> wrote:
>>>>
>>>>>> Attached is dmesg output from booting kernel 3.14-2 (debian unstable)
>>>>>> with drm.debug=0xe and the samsung_laptop module enabled, from my
>>>>>> Samsung N150plus netbook.
>>>>>
>>>>> Have you tried 3.15?
>>>>
>>>> I've built the v3.15 kernel (using the .config file from debian
>>>> unstable and doing make oldconfig).
>>>>
>>>> The backlight is at maximum brightness after boot and I can't control
>>>> it using the backlight buttons, nor by writing to
>>>> /sys/class/backlight/samsung/brightness
>>>> (say half the value or 1/10th of max_brightness)
>>>>
>>>> Backlight does work when writing
>>>> /sys/class/backlight/intel_backlight/brightness
>>>
>>> How about disabling samsung backlight module with 3.15?
>>
>> I'm not sure what you mean by that.
>>
>> As I understand it, there are three ways to control the backlight on this
>> netbook: using intel_backlight, samsung_laptop (using a "sabi" interface)
>> and acpi_video.
>> Backlight control using the samsung_laptop driver no longer seems to work
>> after the change. If I disable it (e.g. by blacklisting it), I expect it
>> to no longer work at all obviously.
>>
>> What do you want me to test exactly?
> 
> If the intel_backlight interface works in 3.15, I presume the problem is
> that you have a non-functional samsung backlight interface that is
> preferred over intel_backlight by your userspace.

I tested the intel_backlight interface in linux v3.15 with the samsung
backlight module blacklisted. The intel_backlight interface still works.

Regards,
Bertrik