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

[Jani Nikula]

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.

BR,
Jani.



>
> Kind regards,
> Bertrik
>
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-- 
Jani Nikula, Intel Open Source Technology Center