Load amdgpu driver
The module parameters of both amdgpu and radeon modules are cik_support= and si_support=.
They need to be set as kernel parameters or in a modprobe configuration file, and depend on the cards GCN version.
You can use both parameters if you are unsure which kernel card you have.
Tip
dmesg may indicate the correct kernel parameter to use: [..] amdgpu 0000:01:00.0: Use radeon.cik_support=0 amdgpu.cik_support=1 to override.
Set module parameters in kernel command line
Set one of the following kernel parameters:
Southern Islands (SI): radeon.si_support=0 amdgpu.si_support=1
Sea Islands (CIK): radeon.cik_support=0 amdgpu.cik_support=1
Furthermore, if you are using an AMD A10 APU with an integrated Sea Island (GCN 1.1) card, you may have to disable Radeon Dynamic Power Management to get a proper boot. This is a feature that dynamically re-clocks the graphics core in order to keep the APU cooler and quieter, however this feature may put you in an infinite restart loop. To disable it, following the instructions above, add radeon.dpm=0 to the boot options.