Yeah -- if you look at the display controller then 4xx/5xx is the logical split, but if you look at acceleration then 5xx/6xx makes a lot more sense.
The radeonhd initiative was driven by the need for modesetting support, while the post-4xx radeon work was driven by the need for acceleration support. We hope the two efforts can pull together over time. I suspect that once we reach a common understanding on requirements, priorities, design / coding practices and the importance of things like kernel modesetting the rest will be easy
