https://bugs.freedesktop.org/show_bug.cgi?id=63935
--- Comment #19 from Alex Deucher agd5f@yahoo.com --- (In reply to comment #18)
(In reply to comment #17)
Make sure you have the updated RLC ucode in addition to the UVD ucode. Unfortunately, I can't reproduce this on the UEFI systems I have access to.
Benjamin and Parag have already indicated which firmware versions they are using, and I feel it's safe to assume that Christian is also using the proper versions as well.
It's worth double checking. I've forgotten to update my ucode a number of times and run into similar problems. Christian was using out of date ucode and when he fixed it his UEFI system started working fine.
We can take a look at register dumps. grab radeonreg: http://cgit.freedesktop.org/~airlied/radeontool/ and dump the regs when booted with legacy vbios vs. UEFI and attach the outputs.
boot with legacy bios (as root): radeonreg regs all > legacy.regs boot with UEFI (as root): radeonreg regs all > uefi.regs