Comment # 22 on bug 69341 from langkamp@tomblog.de

ah sorry - I see radeon.dpm=1 enabled in your log.
My next guess would be to use glamor 0.5.99 AND kernel 3.12 and not
3.11+drmnext

I did NOT test with 3.11 or glamor 0.5.1 and had and have it only working since
3.12rc4 and glamor 0.5.99