Comment 6 for bug 763527

The fix you observed in kernel 2.6.39-rc5 is probably due to this commit. The photo attached to the bug linked in the commit is very similar to your photo.

commit 5785e53ffa73f77fb19e378c899027afc07272bc
Author: Alex Deucher
Date: Tue Apr 19 15:24:59 2011 -0400

    drm/radeon/kms: pll tweaks for r7xx

    Prefer min m to max p only on pre-r7xx asics.

    Fixes:
    https://bugs.freedesktop.org/show_bug.cgi?id=36197

    Signed-off-by: Alex Deucher
    Cc: <email address hidden>
    Signed-off-by: Dave Airlie