https://bugzilla.kernel.org/show_bug.cgi?id=90741
--- Comment #77 from Gustaw Smolarczyk wielkiegie@gmail.com --- No pauses after I applied attachment 166571 and "drm/radeon: do a posting read in si_set_irq" from posting-read branch on top of v3.19. So I guess these commits combined fix this issue.
@Dieter: I did not need to apply this patch in order to fix this issue.