https://bugs.freedesktop.org/show_bug.cgi?id=101026
--- Comment #1 from Harry Wentland harry.wentland@amd.com --- Hi Liam,
I haven't tried it myself but I don't think this will work with the upstream amdgpu driver. You can try Alex's amd-staging-4.9 or amd-staging-4.11 trees and enable CONFIG_DRM_AMD_DC to get support for our new display driver which is not upstream yet. That should give you support for 4k60 over HDMI.
I don't think Mesa has anything to do with this.
Cheers, Harry