https://bugzilla.kernel.org/show_bug.cgi?id=198745
--- Comment #18 from Kyle De'Vir (kyle.devir@mykolab.com) --- Actually, there was a change! Didn't have to boot headless at all, happily.
Your patch didn't seem to change anything, but the update to 4.15.6 might have done something...? Did anything change for Display Core in the latest stable update?