https://bugs.freedesktop.org/show_bug.cgi?id=69723
--- Comment #77 from Alex Deucher agd5f@yahoo.com --- (In reply to comment #76)
Since my last cold boot, I tried with unlimited clocks (reverted previous patches) with hangs almost at start. I tried again with stock 3.13-rc3 with spread spectrum disabled, and I also hit hangs when testing (without having to push the video card with heavy tests). So, for me, disabling spread spectrum may sometimes help, but it is not a real solution to this bug.
Sorry for bringing bad news.
Make sure you try on a cold boot.