https://bugs.freedesktop.org/show_bug.cgi?id=110865
--- Comment #32 from Alex Deucher alexdeucher@gmail.com --- (In reply to Martin from comment #31)
well the flickering goes away, if I lock the clocks to "low" or "high"
Exactly. In that case the mclk never changes so there is no flicker. The mclk has to change during the vblank period otherwise you see flickering. If the vblank periods are not synced up across monitors, you see flickering.