https://bugs.freedesktop.org/show_bug.cgi?id=103791
--- Comment #5 from denisgolovan@yandex.ru --- (In reply to Michel Dänzer from comment #4)
We need to find out why the kernel starts returning -EINVAL from the page flip and wait for vblank ioctls.
Can you try writing 255 to /sys/module/drm/parameters/debug before reproducing the problem, and attach the resulting dmesg output? (Note that writing non-0 to /sys/module/drm/parameters/debug will cause a lot of debugging output to be generated, so you'll want to write 0 to it again soon afterwards)
Got it. I'll attach dmesg as soon as I reproduce the issue.
In case that doesn't reveal why -EINVAL is being returned, are you able to recompile the drm.ko / amdgpu.ko kernel modules with a patch applied?
Sure. Gentoo is there :)