https://bugs.freedesktop.org/show_bug.cgi?id=108781
--- Comment #18 from freedesktop@nuclearsunshine.com --- I just hit this as well with 4.19 on Fedora and a R9 390X - Grub shows fine, then no video output after that (monitor goes into power save), and boot doesn't seem to continue (no disk activity etc.)
I removed amdgpu.dpm=1 from my kernel params and was able to boot with 4.19.x - I noticed that everyone who mentions kernel params on this bug has this param present too - try without it?
This is a regression vs. 4.18.x - with that kernel series I was able to boot with amdgpu.dpm=1 without issue.