Comment # 44 on bug 73530 from Alex Deucher

(In reply to comment #43)
> Would other tests like using a different modeline 1680x1050 be useful? Can
> that be set on the Linux command line? Reading `/sbin/modinfo radeon` I
> could not find the parameter.

The panel has fixed timing so you can only program it with it's native mode. 
All other modes are scaled using the GPU.