Comment # 10 on bug 101988 from Michel Dänzer

(In reply to newincpp from comment #5)
> [  107.804672] amdgpu 0000:01:00.0: SI support provided by radeon.
> [  107.804674] amdgpu 0000:01:00.0: Use radeon.si_support=0
> amdgpu.si_support=1 to override.

Follow this advice and set radeon.si_support=0 amdgpu.si_support=1 to use the
amdgpu driver. (In exchange, you no longer need to blacklist the radeon driver)