https://bugs.freedesktop.org/show_bug.cgi?id=43448
--- Comment #13 from Alex Deucher agd5f@yahoo.com 2012-05-29 15:43:11 PDT --- Created attachment 62246 --> https://bugs.freedesktop.org/attachment.cgi?id=62246 possible fix
It's actually a kernel issue. The attached patch against Dave's drm-fixes branch should fix it.