Linux Mint 15 XORG Compaq 6820s ATI Radeon Rv516

I've spent a lot of time trying to get the video to run at its native resolution of 1440x900 and failed miserably finally succeeded.

Step 1
Change grub to use NOMODESET as described in Installing Mint 14 or Mint 15 Compaq 6820s

Step 2
Add these lines to /etc/init.d/rc.local
modprobe -r radeon
modprobe -r drm
modprobe radeon modeset=1

To give something like this:

#! /bin/sh
### BEGIN INIT INFO
# Provides:          rc.local
# Required-Start:    $remote_fs $syslog $all
# Required-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:
# Short-Description: Run /etc/rc.local if it exist
### END INIT INFO

modprobe -r radeon
modprobe -r drm
modprobe radeon modeset=1


Step 3
Reboot



Credits
I got the solution from this Redhat kernel thread, specifically Comment #104 so thanks to Lyonel Vincent.