https://bugs.freedesktop.org/show_bug.cgi?id=98897

--- Comment #10 from Michel Dänzer michel@daenzer.net --- If you can't or don't want to bisect, there are only 4 radeon driver commits between 4.8.6 and 4.8.7, so it shouldn't take long to try manually reverting each of those. https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/... seems like a good candidate, since it's clock related and explicitly references your GPU in the code.