Some notes after helping to investigate this via IRC: The DDX is stuck in drmmode_set_mode_major during its attempt to unblank the display, because it is waiting for a pending page flip that is never delivered (based on the backtrace provided by Christoph, which I'm attaching for future reference).
** Attachment added: "Xserver-backtrace.txt" https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/1577170/+attachment/4658778/+files/Xserver-backtrace.txt -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1577170 Title: screen cannot be turned back on after being switched off after some time of inactivity To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/1577170/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
