[PATCH v2] drm/amdgpu: Add DC feature mask to disable fractional pwm

[Lukáš Krejčí]

On Mon, 2019-10-21 at 15:44 -0400, sunpeng.li at amd.com wrote:
> From: Leo Li <sunpeng.li at amd.com>
> 
> [Why]
> 
> Some LED panel drivers might not like fractional PWM. In such cases,
> backlight flickering may be observed.
> 
> [How]
> 
> Add a DC feature mask to disable fractional PWM, and associate it with
> the preexisting dc_config flag.
> 
> The flag is only plumbed through the dmcu firmware, so plumb it through
> the driver path as well.
> 
> To disable, add the following to the linux cmdline:
> amdgpu.dcfeaturemask=0x4
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204957
> Signed-off-by: Leo Li <sunpeng.li at amd.com>
> ---
> 
> v2: Add bugzilla link
> 
>  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 3 +++
>  drivers/gpu/drm/amd/display/dc/dce/dce_abm.c      | 4 ++++
>  drivers/gpu/drm/amd/include/amd_shared.h          | 1 +
>  3 files changed, 8 insertions(+)

Tested on Ubuntu 19.04, vanilla v5.3.7 kernel with the patch applied
and amdgpu.dcfeaturemask=0x4 added to the kernel command line, no
issues after 8 reboots. (The issue could be reproduced without
amdgpu.dcfeaturemask=0x4 on first boot.)

Tested-by: Lukáš Krejčí <lskrejci at gmail.com>