Yes! I finally made it work – or at least constructed the right combination of search words for google to help me 🙂

At work I have a Dell Latitude D610 laptop, a docking station and a 20″ Dell flat panel. For the longest time I have tried to combine the two displays with both the radeon driver and later on ATI’s proprietary fglrx driver.

The only success I’ve had with the radeon driver is using the merged framebuffer together with a VGA cable, but that results in a not-so-nice image quality on the flat panel. I also had it working for two days with the DVI cable, but the next day the internal display in the laptop was dead, so I can’t recommend that option 😳

The proprietary fglrx driver that ships with Ubuntu Dapper (and most other linux distributions) is easy to configure, unfortunately it contains some bugs that triggered in my particular setup.
What I want is a resolution of 1400×1050 on the laptop and 1600×1200 on the flat panel. There’s a bug in the last few versions of the driver though, that makes it hard to do this, since it defaults the resolution of the second display to the resolution of the first display. This results in a resolution of 2800×1050 and garbage on the rest of the space on the second display.

Luckily, this page has a work-around for the problem. The solution is quite genius and uses one of the fglrx driver’s shortcomings to our advantage. When the driver is in big desktop mode it doesn’t support the Virtual parameter in the Display configuration – at least as you would expect. By specifiying a virtual size the driver will magically use the complete 1600×1200 resolution on the second display and I get what I want – full utilization of my displays.

The only problem with this solution is when the laptop is not docked and only have the internal display available. The driver is in single-head mode and accepts the Virtual configuration, creating a scrollable view port. This is easily fixed with the following command, though.

$ sudo xrandr -s 0

Have a peek at my xorg.conf for configuration details.