Comment # 9 on bug 109246 from tme

I've tested some more kernels, all from
https://kernel.ubuntu.com/~kernel-ppa/mainline/.

Setting amdgpu.dc=1 on 4.15.18 and 4.16.18 does not reproduce the problem. It
does, however, reproduce on 4.17.19.

Also, I now believe my HDMI monitor may have polling, as it cycles through each
input once when it no longer detects a signal.

Please let me know if there is anything else I can help with.