https://bugs.freedesktop.org/show_bug.cgi?id=58667
--- Comment #21 from Thomas Rohloff v10lator@myway.de --- Here's my final summary:
If http://cgit.freedesktop.org/mesa/mesa/commit/?id=6532eb17baff6e61b427f29e076... and cgit.freedesktop.org/~agd5f/linux/commit/?h=drm-next-3.8&id=dd54fee7d440c4a9756cce2c24a50c15e4c17ccb is missing the bug doesn't trigger. If the first one is there the bug is triggered extremely often, spamming dmesg. If only the second is there the bug triggers randomly (good way to trigger: Lot of exploding TNT in Minecraft. Just build TNT pillars and ignite them till you are at bedrock).
My last hope is that some genius hacker which knows the driver has some "ah, I see the problem" moment. :(