xorg-server-dummy: cannot add additional xrandr mode (xrandr: Configure crtc 0 failed)

[Nicolas Boichat]

Hi,

I'm running a dummy X11 server (Xorg 1.15.1 on Ubuntu 14.04), using
the configuration attached.

I am able to change resolution using xrandr, as long as I use the ones
that are setup when the server is started (either the default ones, or
the ones I add in the Monitor section).

I'd like to be able to add new arbitrary resolutions using output from
gtf, but this fails:
# xrandr --newmode 800x632_60.00 40.24 800 832 912 1024 632 633 636
655 -HSync +Vsync
# xrandr --addmode default 800x632_60.00
xrandr: Failed to get size of gamma for output default
(I guess this is harmless: the mode is added)
# xrandr --output default --mode 800x632_60.00 --verbose
xrandr: Failed to get size of gamma for output default
crtc 0: disable
screen 0: 800x632 211x167 mm  96.09dpi
crtc 0: 800x632_60.00   60.0 +0+0 "default"
xrandr: Configure crtc 0 failed
crtc 0: disable
screen 0: revert
crtc 0: revert

A similar method works fine with intel drivers.

Any idea if this is supposed to work, or if I am doing something
wrong? Or is this something that the dummy driver does not support?

Thanks a lot for your help,

Best regards,

Nicolas
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