It sounds like the fairly typical error that UXA is eating the vblank notification whilst DPMS off and not informing the client that they are no longer ignored.
How about trying Option "Triplebuffer" "false"? -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1273832 Title: [i915] Lockscreen/lid-close xserver freeze if UXA accel used. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-intel/+bug/1273832/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
