[Bug 111483] FreeSync LFC breaks under certain circumstances, causing either tearing or stutter

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=111483

            Bug ID: 111483
           Summary: FreeSync LFC breaks under certain circumstances,
                    causing either tearing or stutter
           Product: DRI
           Version: DRI git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: not set
         Component: DRM/AMDgpu
          Assignee: dri-devel at lists.freedesktop.org
          Reporter: tempel.julian at gmail.com

I've noticed that there sometimes was tearing (vsync off) when framerate was
below VRR range minimum (which is 40 - 144Hz in my case), e.g. in some game's
videos that run with 30fps and probably also if framerate rapidly drops below
VRR range.

I found a way to reliably reproduce the issue during actual game rendering:
Start vkquake and load a level. Game's default limiter is set to 200. Open
game's console via tilde key (English keyboard layout, button below ESC) and
set fps to 35 (should be below any display's VRR range minimum) by typing
"host_maxfps 35".
-> FreeSync LFC should be broken now and show tearing if vsync isn't turned on.
When changing again to a value that's inside the VRR range, e.g. 100, VRR works
perfectly again. When switching back to 35, it's once again broken.
The Windows driver doesn't seem to show this issue.

linux 5.2.9 (also tested drm-next branch)
xf86-video-amdgpu-git e6fce59a071220967fcd4e2c9e4a262c72870761
RX 570
radv of mesa-git ACO branch fc0fdb637b4a028816f5a59b14eda07612e1bc9b

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