Flaky brightness on Renoir

Harry Wentland hwentlan at amd.com
Wed May 20 22:07:54 UTC 2020

On 2020-05-20 6:03 p.m., Koo, Anthony wrote:
> [AMD Official Use Only - Internal Distribution Only]
> Hi Harry,
> It does sound like a firmware issue.
> I think we will need to do some investigation here. I would be curious if this is a driver regression or just never worked (not sure how new the driver being tested is).
> This point below seems to indicate the firmware might be using some uninitialized values in some if its calculations.
> Typically these value would be things like backlight characteristic curves that are passed to the firmware via a table generated in the power helpers file, and programmed in our dc code.

Do you think this could be related to Wyatt's endian-ness fixes?


> I'm not 100% sure this is the problem, but it could be something we can take a look at from dmcu_load_iram.
>>> 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.
> Thanks,
> Anthony
> -----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?
> Thanks,
> Harry
> 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,
>>> _______________________________________________
>>> amd-gfx mailing list
>>> amd-gfx at lists.freedesktop.org
>>> https://lists.freedesktop.org/mailman/listinfo/amd-gfx

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