amdgpu driver, Screen artifacts on >=75 Hz FHD display unless forced power state, if there was >=75 Hz when Xorg started.

[Piotr Karbowski]

Hi,

I am facing a common issue with a screen artifacts whenever I start my Xorg on AMDGPU driver with display set to 75 Hz 1920x1080. It appears to be hitting all the users of AMDGPU driver.

    https://bugs.freedesktop.org/show_bug.cgi?id=96868
    https://bugs.freedesktop.org/show_bug.cgi?id=102646

Here I am running the Polaris, RX 580 8G variant.

I've noticed that if I disable freesync *before* starting Xorg, which makes my Xorg starts with default 60Hz, I have no screen artifacts. If however I start Xorg with freesync on (in monitor), XOrg defaults to 75 Hz and I have random screen tearing and artifacts. What is worth a note is that if I enable freesync and/or change from 60 Hz to 75 Hz after Xorg started, I have no screen artifacts. Same goes if I switch to 60 Hz via xrandr and/or disable freesync in Monitor OSD during Xorg run time, the screen artifacts still happen.

Forcing power state to lowest with

    echo low >/sys/class/drm/card0/device/power_dpm_force_performance_level

Does make the screen artifacts go away, during runtime, without restart.

I found it a bit surprising that it appears it's about the state of monitor/default frequency  of the moment when Xorg was started rather than the the currently running frequency of the screen. As with low mode, I Have 300 MHz on mclk and sclk and no screen artifacts it may mean that it's not about not enough power on the GPU to handle it, rather than something that happens when the power states switches.

Some additional information:

- I am running simple openbox WM
- Vanilla 4.19.2 kernel
- x11-drivers/xf86-video-amdgpu-18.1.0
- x11-base/xorg-server-1.20.3

Would you kindly share your thoughts about above problem?

-- Piotr.