https://bugs.freedesktop.org/show_bug.cgi?id=106940
--- Comment #27 from Przemek soprwa@gmail.com --- Now it is in stable 4.18. Same situation here. Gentoo ~amd64 on Lenovo G50-45 A6-6310 APU with R4 Mullins.
Laptop monitor is off (eDP), but there is picture on external one, connected through hdmi port.
Reverting troublesome commit (drm/amd/display: Use dig enable to determine fast boot optimization.) make things work again.