The first 900+ pages of specifications have been delivered!
Ending off the X Developer Summit this year, Matthew Tippett handed off ATI's GPU specifications to David Airlie on a CD (as reported by Daniel Stone). However, the specifications are also now available on the Internet! At http://www.x.org/docs/AMD/
is the location of the documentation where you can freely download the files. Right now there is the RV630 Register Reference Guide and M56 Register Reference Guide. The RV630 Reference Guide is 434 pages long while the M56 Guide is 460 pages. Expect more documentation (and 3D specifications) to arrive shortly. The new open-source R500/600 driver will be released early next week. More information to come soon.