I have nothing useful to add other than 4K60 on Kubuntu 19.04 (5.0.0-25) works fine for me out of the box on an RX 570. I’m connected over DP. Are there any 4k monitors out there that can only do 30hz over HDMI and 60 over DP?
Update: I’ve been able to decode the EDID from the display link here: http://ix.io/1VcO . It appears that what’s happening is that in Linux it is stuck in RGB mode, and I need YCbCr 4:2:0 in order to get 60hz @ 4k. It’s there in the EDID so I’m not quite sure why the kernel isn’t seeing it
You might just need a better cable, you don’t want to be converting the output to anything other than full RGB if you can avoid it. Assuming this card supports HDMI 2.0
Pretty sure the most the display handles is that 297 Mhz…Windows handles it just fine. There has got to be a way to tell the kernel I’ve got a YCbCr 4:2:0 mode here. I’ve already tried multiple cables.