GNOME Bugzilla – Bug 700594
Monitor on second video card doesn't display anything after login
Last modified: 2013-05-20 20:06:33 UTC
From downstream https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1178000 I have a third monitor attached to a second video card, the monitor fails to display anything after logging in. To get it to work display anything I have to disable it, then re-enable it. Not sure if this is a gnome-shell issue or clutter/mutter. Both my cards are Radeon HD 4850, using the free drivers. ProblemType: Bug DistroRelease: Ubuntu 13.04 Package: gnome-shell 3.6.3.1-0ubuntu6 ProcVersionSignature: Ubuntu 3.8.0-20.31-generic 3.8.11 Uname: Linux 3.8.0-20-generic x86_64 ApportVersion: 2.9.2-0ubuntu8 Architecture: amd64 Date: Wed May 8 15:58:15 2013 DisplayManager: lightdm mutter: 3.6.3-0ubuntu2 0
Created attachment 244643 [details] Xorg log
I don't think X supports more than 1 GPU in the same X11 screen. That means that running a single desktop spanning monitors connected to more that 1 GPU doesn't work. Yet, at least. In any case this isn't a mutter bug.
It does support more than one GPU in the same X11 screen, but gnome-shell didn't support multiple GPUs until recently. The reason I filed it under mutter was because of this bug: https://bugzilla.gnome.org/show_bug.cgi?id=648156 I'll do a little more digging to see if this is a gnome-shell issue.
If everything works as expected after disabling and reenabling the display in System Settings, then this is a bug in the X server, in gnome-settings-daemon, or (less likely) in the Mesa GL drivers. (In the case where the display isn't working, do 'xdpyinfo| grep dimensions' - if the monitor's pixels show up there, then it might be a Mesa bug, but if they don't show up, then that excludes Mesa and it's either an X or g-s-d bug)
I sometimes have to disable/reenable the monitor multiple times before I can get it to work. There are three cases that I get when I enable/reenable the monitor: 1 : Works as expected, I get a screen that spans all three monitors 2 : The screen is shifted by about half the width of the third monitor 3 : Similar to 3, except that the middle monitor displays corrupt graphics. This is what I get on case 1, and before I've done the disable/reenable. $ xdpyinfo |grep dimen dimensions: 5520x1080 pixels (1461x286 millimeters) I also tested in Ubuntu Unity with the same results, so that rules out gnome-shell. What's my next step for ruling out Mesa / X / g-s-d?
Created attachment 244858 [details] xrandr output
@Owen Taylor, I've attached my xrandr output from when I have all three monitors working, and it is identical to when the third one is displaying black. I've also tried using xfce as a desktop without compositing, and have similar results. If I have an xrandr command run on my session login to set the monitors, then it works fine. What else can I do to diagnose which package this bug belongs to? Thanks, Richard.