I'm getting exactly this issue. An ATI RX 480 on Kubuntu 18.04 with a ASUS MG28U on HDMI-1. It is on a 5m cable so using the displayport wasn't an option. The long HDMI cable is to allow the large system box to be away from my desk. I mostly use the system as a web and data server and it is stuffed with hard drives.
Works perfectly on 4.13 kernels. Fails on the 4.15 kernels before the sddm login screen. 4.15.0-43-generic <-- screen repeats HDMI no signal 4.15.0-42-generic <-- screen repeats HDMI no signal 4.15.0-35-generic <-- screen repeats HDMI no signal 4.13.0-36-generic <-- ok On 4.13 kernels it runs the screen at 3840x2160 @ 30Hz. On 4.15 kernels it doesn't. At a guess looking at the syslog, the 4.13 fell back to 30Hz at the hi- res while the 4.15 does not. Over the long cable the screen isn't detecting the screen at 60Hz. Hope that helps. I may have to look at getting a longer active cable... ** Attachment added: "syslog_fragment_4.15.0.43.txt" https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1761751/+attachment/5221404/+files/syslog_fragment_4.15.0.43.txt -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1761751 Title: Black screen on 18.04 + AMD RX460 To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1761751/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
