Comment # 1 on bug 107613 from J. Andrew Lanz-O'Brien

Update: this bug is still present as of kernel 4.20.0-arch1-1-ARCH #1 SMP
PREEMPT Mon Dec 24 03:00:40 UTC 2018 x86_64 GNU/Linux

Setting amdgpu.dc=0 in the GRUB command fixes the issue, but then HDMI audio
doesn't work.