https://bugs.freedesktop.org/show_bug.cgi?id=107613
--- Comment #1 from J. Andrew Lanz-O'Brien jlanzobr@gmail.com --- 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.