Flaky brightness on Renoir

Chiu, Michael Michael.Chiu at amd.com
Thu May 21 14:51:43 UTC 2020

[AMD Official Use Only - Internal Distribution Only]

Hi Harry,

" Michael, does this "fix" your issue?"

Yes, the change "fixes" the issue.  It has the same effect as removing renoir_dmcu.bin work-around, where backlight control starts to work.

Thanks again,

-----Original Message-----
From: Wentland, Harry <Harry.Wentland at amd.com> 
Sent: Wednesday, May 20, 2020 5:53 PM
To: Alex Deucher <alexdeucher at gmail.com>; Alexander Monakov <amonakov at ispras.ru>; Kazlauskas, Nicholas <Nicholas.Kazlauskas at amd.com>; Li, Sun peng (Leo) <Sunpeng.Li at amd.com>
Cc: amd-gfx list <amd-gfx at lists.freedesktop.org>; Deucher, Alexander <Alexander.Deucher at amd.com>; Chiu, Michael <Michael.Chiu at amd.com>; Koo, Anthony <Anthony.Koo at amd.com>
Subject: Re: Flaky brightness on Renoir

We've seen similar problems internally.

Michael, does this "fix" your issue?

Anthony, looks like smooth_brightness is problematic on (some) renoir systems. Thoughts?


On 2020-05-20 5:47 p.m., Alex Deucher wrote:
> Adding some display people.
> On Wed, May 20, 2020 at 5:46 PM Alexander Monakov <amonakov at ispras.ru> wrote:
>> Hello,
>> I have a laptop with the recent Renoir SoC. Screen brightness is 
>> controlled via the amdgpu driver. Unfortunately it doesn't work
>> properly: brightness doesn't go below a certain threshold. In one 
>> experiment I've found the threshold to be about 95 (of 255), which is 
>> quite high.
>> There's a bugreport on the tracker from a person with the same laptop 
>> model as mine that says that the threshold may vary from boot to boot.
>> So far I was able to find a workaround: avoiding 
>> dmcu_set_backlight_level like in the patch below gives more reliable 
>> backlight control (but at the expense of breaking "actual_brightness"
>> sysfs file, because it reads from DMCU registers).
>> What might be the problem and can I help investigate this further? 
>> Would really like to see this work properly.
>> Alexander
>> diff --git a/drivers/gpu/drm/amd/display/dc/dce/dce_abm.c 
>> b/drivers/gpu/drm/amd/display/dc/dce/dce_abm.c
>> index b8a3fc505c9b..3274b0d15893 100644
>> --- a/drivers/gpu/drm/amd/display/dc/dce/dce_abm.c
>> +++ b/drivers/gpu/drm/amd/display/dc/dce/dce_abm.c
>> @@ -428,7 +428,7 @@ static bool dce_abm_set_backlight_level_pwm(
>>                         backlight_pwm_u16_16, backlight_pwm_u16_16);
>>         /* If DMCU is in reset state, DMCU is uninitialized */
>> -       if (use_smooth_brightness)
>> +       if (0 && use_smooth_brightness)
>>                 dmcu_set_backlight_level(abm_dce,
>>                                 backlight_pwm_u16_16,
>>                                 frame_ramp, 
>> _______________________________________________
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