https://bugzilla.kernel.org/show_bug.cgi?id=196117
--- Comment #1 from Paul K. Gerke (paulkgerke@craftware.nl) --- I just realized that while trying to be concise, I deprived this bug report of a lot of information:
The very short version:
The AMDGPU driver somehow causes the system to hang after initramfs, after the kernel was loaded, but VERY early in the boot sequence. Within the first 100 milliseconds or so during regular boot, when the system normally switches to its graphics driver, my monitor goes black and the system just hangs. No communication possible. As stated above, the monitor stays on, so there is some sort of graphics signal.
With the "nomodeset"-option, this issue is gone and the system comes up normally.
This happens on all modern kernels, with different linux distros. I currently tried Xubuntu (16.04, 17.04), Ubuntu (17.04), and Arch Linux. I forgot which kernel versions I exactly tested, if relevant I can list them, but the result seemed all the same.