Since kernel 4.18.0-rc1, my laptop boots in a black screen with Kaveri+Topaz
GPUs, Xorg 1.20.0. The systems boots normally in the background. I can log in
blindly in sddm, press CTRL+ALT+DEL when KDE has booted invisibly and shutdown
the laptop with ENTER. I'm using the following options :

install radeon /bin/false
options amdgpu dc=1 si_support=1 cik_support=1
options radeon si_support=0 cik_support=0

Everything was just working until 4.18.0-rc1.

If I boot on another partition, I can inspect Xorg.0.log of the main partition,
which contains no errors.

With no options at all, or if dc=0, I can get a KDE usable session, excepting
suspend failing quite often.

Thanks for any input to resolve this. I can give more information upon your
instructions.