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

[Jani Nikula]

On Fri, 22 Aug 2014, Bertrik Sikken <bertrik at sikken.nl> wrote:
> 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.

I read that as, "I no longer have problems with backlight".

Jani.


>
> Regards,
> Bertrik

-- 
Jani Nikula, Intel Open Source Technology Center