Thanks to some great work by Maciej Cencora we have initial support for 3D on the RS690 chipset. The level of support is the same as the current rs4xx chipsets, i.e. glxgears works, some other 3D apps should work, compiz doesn't work.
The changes are in the drm and Mesa master trees now and require the latest xf86-video-ati radeon DDX. I'll be getting a real rs690 post-LCA and my first task is to try and fix the r300 3D driver bugs that are stopping compiz from working, and hopefully fix a few bugs with some other 3D applications.
The RS690 is a hybrid chip with the r5xx era modesetting core combined with an r4xx 3D core with no vertex-shader/tcl support.