Recently built an all AMD system with Ryzen 3700x and Vega 56. Currently running Manjaro 20.01 GNOME. I have 4K monitors connected via Displayport.
I have the displays set to go to blank after 12 minutes of idle. Occasionally upon resume, my second monitor is blank. It powers back up when I hit the keyboard but nothing displays. The monitor continues to appear as connected in my GNOME Display settings but shows nothing on the screen.
I can change inputs to other connected machines and those work fine but returning new machine connected to the Vega 56 is still blank. Power cycling the monitor has no effect either. Unplugging and re-plugging the cable at the GPU and the monitor has no effect; still blank. So far the only thing I know to do is reboot - then the display works again.
My first guess was that this may be related to power management so I tried disabled DPM, BAPM. The problem didn’t happen for over a day so I thought I had it resolved but it just happened again. I just set ASPM to 0 so we’ll see if that has any impact but wondering if there are any other Vega 56 on Linux users out there who have wrestled with similar challenges.