Tonga PRO [Radeon R9 285/380] [1002:6939] blank screen

[Steven Falco]

I have a Radeon R9 285/380 video card in a machine that is running Fedora 26.  When I run with Fedora kernel version 4.11.11 the video card works properly, using the amdgpu kernel driver.

However, once I upgrade to a newer kernel in the 4.12 or 4.13 series, my display goes blank during boot and stays that way.  The monitor appears to be getting sync, because it doesn't go to sleep, however there is nothing visible on the screen.

What information should I post to this list to help diagnose the problem?

	Thanks,
	Steve