I'm having the same issue, on exactly the same machine as Aljaž Prusnik in comment 31.
Machine is Dell XPS 9550 with i7-6700hq, kernel is 4.5.1 (from testing on Arch Linux, using the X modesetting driver) When starting X with external display attached and using xrandr it a) takes very long to apply the mode, over 5 seconds b) very often leaves the internal display completely black When I move the mouse when it is in this mode, it'll lockup, leaving me to only be able to poweroff the machine. When I redo xrandr without moving the mouse, and get it to work on both screens, it'll work without problems after that. The lockups also happen after the screens wake up from DPMS power save. It's not happening with a 4.4 kernel, but this one has other problems, like endless flickering on the external display after a DPMS wakeup. I'm really eager to have that patch, but since the merge window for 4.6 is already over, does this come with 4.7 the earliest? -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1523088 Title: WARN_ON(!wm_changed) warning and stacktrace in kernel log To manage notifications about this bug go to: https://bugs.launchpad.net/xorg-server/+bug/1523088/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
