https://bugs.freedesktop.org/show_bug.cgi?id=106175
--- Comment #64 from Nicholas Kazlauskas nicholas.kazlauskas@amd.com --- Created attachment 142574 --> https://bugs.freedesktop.org/attachment.cgi?id=142574&action=edit 0001-drm-amd-display-Add-fast-path-for-legacy-cursor-plan.patch
This patch is similar to the async_update one but it takes care to lock if anything is modifying the plane. It's very close to what i915 does with a few minor differences with framebuffer handling.
I've tested it for compton with Gallium HUD up and I no longer see the issue on mouse movement (cursor fb changes are still a bit slow, so you'll still probably see spikes on cursor changes).
You can try this on top of amd-staging-drm-next and I'd imagine it'd fix your problems.