No backlight since linux-4.2.4 - drivers/gpu/drm/radeon/atombios_encoders.c

[Alex Deucher]

On Tue, Oct 27, 2015 at 6:06 AM, Michael Burian <michael.burian at sbg.at> wrote:
> On 10/27/15 10:17, Michel Dänzer wrote:
>>
>> I'm not familiar with the ATOM bytecode, but since the number of
>> bytecode instructions executed seems the same in both cases, I suspect
>> that dig->backlight_level == 0 => ATOM_LCD_BLOFF is executed. (The
>> debugging output in my patch would have provided all of this information
>> and more, but there wasn't any of it in the dmesg you provided)
>>
>> I guess the question then becomes how dig->backlight_level is (supposed
>> to be) initialized.
>>
>> What values do the following files contain in the broken and working cases?
>>
>> /sys/class/backlight/radeon_bl0/bl_power
>> /sys/class/backlight/radeon_bl0/brightness
>> /sys/class/backlight/radeon_bl0/actual_brightness
>> /sys/class/backlight/radeon_bl0/max_brightness
>>
>>
>
> These files do not exist on my system,
> I can offer /sys/class/backlight/acpi_video0/
>
> content is identical in both cases
>
> bl_power        0
> brightness      10
> actual_brightness       10
> max_brightness  10
>
>

It would appear that your system does not use the gpu backlight
controller.  Either it's lying or messing with the GPU backlight
controller causes some bad interaction with whatever does control it.
Does the attached radeon patch help?  I'm also attaching an amdgpu
patch for reference in case the same problem appears on amdgpu.

Alex
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