I have xfce power manager set to manage my display settings. If I am running the 4.4.x series of kernels (confirmed under 4.4.1 through 4.4.4), xfce4 does not allow my monitor to wake from standby mode. The only way to wake it is to drop to a TTY and restart lxdm. Interestingly, if I downgrade my kernel to 4.3.6, everything works as it should. I believe this bug to be unique to xfce4 because if I log into Gnome under kernel version 4.4.4, the monitor sleeps and wakes normally. I only experience this under the xfce4. Attached you can find my Xorg.log and ~/.xfce4-session.verbose-log after the monitor has been played in standby mode and refused to wake up. I am happy to include any other logs or troubleshooting info. Hardware details: CPU: i7-4790K (Haswell) with onboard graphics) connected via HDMI to monitor. Monitor: Asus PB278. Motherboard: MSI Z97 MPOWER MAX.
Created attachment 6624 Xorg log
Created attachment 6625 xfce4-session.verbose-log
Same problem here. It happens only when my laptop is docked whether the lid is closed or not. It happens only when using Xfce, no problem with Gnome or Trisquel. Thinkpad x200 running Libreboot and Trisquel 7 kernel : 3.13.0-79-lowlatency external monitor : Samsung with Display port.
I am very happy to troubleshoot if someone can provide a specific experiment to run. I can also confirm this bug is present under linux v4.5.0.
I see the same problem with 4.4.x kernels on 4790K with the integrated intel video. Downgraded to 4.2.3-300 kernel and the problem went away. I have also observed that the problem doesn't occur if xfce is not running, like, for example, the lightdm greeting screen doesn't exhibit similar problems.
Perhaps bug #11107 is to blame for this behavior (pointed out by ToZ on the forums). I applied the patch[1] from comment number 53 in the #11107 to xfce4-settings and have thus far successfully awakened my monitor 3 out of 3 tries under kernel v4.4.6. I will preform more tests before calling this solved, but wanted to document this in the ticket. @Az and Steve - Can you guys try it and report back? 1. http://bug-attachment.xfce.org/attachment.cgi?id=6590
Dozens of sleep/wake cycles now. I'm calling this solved by virtue of the patch referenced in comment #6.
@John: I report that the patch helped me. Is it going to be released soon or should I push for my distro (Fedora) maintainers to add it?
I have no idea about when or if the patch will be accepted into xfce4 upstream. You will need to near back from the owner (no one is assigned as far as I can tell).
I applied the patch referenced in https://bugzilla.xfce.org/show_bug.cgi?id=12480#c6 and my monitor does wake up now, so that's good. I am kind of curious about what would have changed between 4.2 and 4.4 kernels that makes this fix necessary.
Awesome, so it was a bug/fix in xfce4-settings not the power manager.