Bug#661943: xserver-xorg-video-radeon: Unable to set native resolution with KMS enabled
Unfortunately, my problem is that I can't change the display modes to the native resolution. Even with one display disabled, I still can't set the native resolution. I get the same "input timing not supported" message every time I have tried.
It wouldn't be a problem if the default was not what I wanted but I could change to the correct resolution.
Most of my attempts to change the resolution have been been using the KDE display tool (which, as I understand, uses xrandr underneath). However, I've also attempted to use xrandr directly.