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 Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1761751 Title: Black screen on 18.04 + AMD RX460 Status in linux package in Ubuntu: In Progress Status in linux source package in Bionic: In Progress Bug description: I've been running 16.04 + hwe kernel 4.15 for a while now and recently I'm now having a black screen instead. I've also tried an 18.04 daily live USB stick, which has the same issue. It probably started during an upgrade this week or last week. As a start I'm blaming the Linux kernel since booting a 4.13 kernel works just fine. Known faulty kernel versions are: * linux-image-4.15.0-041500-generic (mainline kernel), * linux-image-4.16.0-041600-generic (mainline kernel), * linux-image-4.15.0-13-generic (Ubuntu kernel), * whatever comes with 18.04 daily live USB stick as of 20180404. Not sure how to best collect logs and system information for you since I'm not used to debugging black screens, so I'm just attaching lspci as a start. EDIT: Workaround found by adding "amdgpu.dc=0" to kernel boot parameters. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1761751/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
