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)
radv of mesa-git ACO branch fc0fdb637b4a028816f5a59b14eda07612e1bc9b
I think there is a realistic chance that this issue has been tackled by this commit:
However, I don't own an LFC capable display anymore and can't test.
Though I think it might be a candidate for backporting to 5.4?