Just for reference, this error comes from the line: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/radeon/r600.c#n2848 Basically, the r600 driver writes 0xCAFEDEAD into a scratch register, then uses a ring write to try and write 0xDEADBEEF into the scratch register, and then waits and then reads the scratch register again to see what is in it. If it is not 0xDEADBEEF, then the test fails and hardware acceleration is turned off. The important question is why is the ring write failing, and I don't have an answer.