Dual Monitors in KDE4 with Radeon RV516

I just switched from using Gnome at work to using KDE4, which unfortunately meant that I lost my dual-screen setup.  While that doesn’t make much sense, it turns out to be possible to get it back without.having to change too many things or change to proprietary drivers.

This is all done with an ATI Radeon RV516 video card, which has one dvi output which has a sort of y-adaptor to 2 VGA connectors, one for each monitor.    The default KDE behaviour was that krandrtray and the display settings both claimed there was a single monitor with both DVI-0 and DVI-1 on that same monitor when identifying displays.

Here’s what I did to fix it:

  1. make sure the radeon driver is installed on your system – it is included in the 2.6.31 ubuntu kernel by default
  2. add the ‘radeon’ driver to the end of /etc/modules so it will be loaded on boot:
    radeon # this is all that is needed
  3. install the radeon and radeonhd xserver-xorg-video packages (you probably only need one or the other):
    apt-get install xserver-xorg-video-radeon xserver-xorg-video-radeonhd
  4. restart kdm (and thereby the X server):
    sudo service restart kdm
  5. Log in and determine that KDE runs just like before, with mirrored screens
  6. open a terminal and run the command:

    xrandr --output DVI-0 --left-of DVI-1 --mode 1280x1024
  7. play around with the xrandr parameters if it’s not quite right
  8. add that xrandr line to run on kdm startup by adding it to /etc/kde4/kdm/Xsetup

Don’t edit your xorg.conf at all – the default single screen and single device sections in there are fine the way they are.   Tada, dual-screen awesomeness!