I've been having issues getting xorg-server configured on the U3, and I haven't found a way without having to resort to using patches from forums all over the place.
These are the packages that I install:
xf86-video-armsoc-odroid
xf86-video-fbdev
odroid-libgl
xorg-server
This is what I get:
http://pastebin.com/ELqn9QjQ
this is my xorg.conf: http://pastebin.com/T0vzS7QM
Any ideas?