In order for xrandr to support extended desktops on dual-head configurations it is necessary to add the Virtual flag to the Display SubSection. When this flag is added Xorg freezes at greeter screen (GDM) and the keyboard becomes unresponsive. Steps to Reproduce: 1. Install a version of Linux with X.org 7.4 (Fedora 10 in my case) 2. Make sure that your default dual-head (cloned) configuration works. 3. Switch to runlevel 3 4. Create a default xorg.conf for the system with X -configure 5. Copy the output file to /etc/X11 6. Edit the appropriate Display SubSection adding the Virtual flag. 7. Save configuration and switch to runlevel 5 8. Xorg freezes at GDM greeter screen Hardware used to reproduce the problem: System is a HP Compaq dc7800 with integrated Intel graphics and ADD2 extender card (2nd port).
I think Fedora 10 kernel uses GEM. So this might be the current GEM limitation, as mentioned in bug#17490. You can try a smaller Virtual value to see if it works. That'll tell if it's a problem by using Virtual option, or just the specific big size.
Gordon, Maybe the bug is related, but it does not appear to be. If I add the option "noaccel" option to the intel driver section, GDM does not freeze and I can use xrandr to configure a spanned desktop.
"noaccel" option also works for bug#17490. So I think they are dup. *** This bug has been marked as a duplicate of bug 17490 ***
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