[Bug 110510] Radeon VII HDMI issues: Flicking/system crashing

[bugzilla-daemon@freedesktop.org]

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https://bugs.freedesktop.org/show_bug.cgi?id=110510

            Bug ID: 110510
           Summary: Radeon VII HDMI issues: Flicking/system crashing
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: tom@r.je

Created attachment 144089
  --> https://bugs.freedesktop.org/attachment.cgi?id=144089&action=edit
dmesg after setting HDMI screen to 59.94hz

I have a radeon VII with two 4k displays. One connected via HDMI and one
connected via DisplayPort. Neither monitor supports freesync.

Linux 5.0.9 
Mesa 19.0.3

The DisplayPort monitor is working fine.

The HDMI monitor has some problems. On its own I can get it working perfectly.
Here's the output from xrandr:

DisplayPort-2 connected primary 3840x2160+0+0 (normal left inverted right x
axis y axis) 521mm x 293mm
   3840x2160     60.00*+  30.00    30.00    24.00    29.97    23.98  
   1920x1200     60.00  
   1920x1080     60.00    50.00    59.94    30.00    24.00    29.97    23.98  
   1600x1200     60.00  
   1680x1050     59.95  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x960      60.00  
   1280x800      59.81  
   1152x864      75.00  
   1280x768      59.87  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  
HDMI-A-0 connected 3840x2160+3840+0 (normal left inverted right x axis y axis)
521mm x 293mm
   3840x2160     60.00*+  60.00    50.00    59.94    30.00    30.00    24.00   
29.97    23.98  
   1920x1200     60.00  
   1920x1080     60.00    50.00    59.94    30.00    24.00    29.97    23.98  
   1600x1200     60.00  
   1680x1050     59.88  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x960      60.00  
   1280x800      59.91  
   1152x864      75.00  
   1280x768      59.87  
   1280x720      60.00    50.00    59.94  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00  
   720x480       60.00    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94  
   720x400       70.08  


If it's connected on it shows two problems intermittently:  

1. It flickers occasionally with visual artifacts
2. The screen goes black for a few seconds then comes back


With just the HDMI screen connected this can be solved. If I set the refresh
rate to 59.94 the problems go away and everything is working flawlessly. 

However, as soon as I connect the second monitor by displayport this fix  no
longer works.

With both monitors connected and both running at 60.0hz, the displayport screen
is fine but the HDMI screen flickers. An easy fix I thought: Run the HMDI
screen at 59.94hz and the flicker will go away.


Unfortunately, what actually happens is the entire session freezes after a few
seconds on both X and Wayland. Usually it requires a complete system reset but
I have managed to recover from it a couple of times and I've attached my dmesg
output.

Sometimes the freeze is instant, other times I get up to 10 seconds before the
system freezes.


I also tried 50hz on the HDMI monitor and the same thing happened.

There appears to be two different issues here:


1. HDMI flickers 
2. Running two monitors at different refresh rates causes the driver to crash

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