4k hdmi monitor stays black on kaveri [regression]

Submitted by Clemens Eisserer

Assigned to Default DRI bug account

Link to original bug (#107072)

Description

After updating Fedora 28 on my Kaveri System (A8-7650K) with AMDGPU enabled from 4.16.16 to 4.17.2 my 4K HDI display stays black (the FHD display connected via HDMI continues to work as expected).

Please let me know what kind of information is required find the root cause.