I'm using an RX 480 and also have the same problem on kernels 4.18 and 4.20 (tested using 4.20.0-042000 from https://kernel.ubuntu.com/~kernel-ppa/mainline/v4.20/). Adding "amdgpu.dc=0" to GRUB fixes the problem in both cases.
I'm using an RX 480 and also have the same problem on kernels 4.18 and 4.20 (tested using 4.20.0-042000 from https:/ /kernel. ubuntu. com/~kernel- ppa/mainline/ v4.20/). Adding "amdgpu.dc=0" to GRUB fixes the problem in both cases.