Back on September 6th of this year AMD shocked the open-source community by committing to the development of a new open-source display driver (this driver is now known as RadeonHD) and that they would be providing specifications to the development community. A week later, they set precedence by not only releasing the documentation to the developers but to the everyone! Their first batch of documentation covered the basics for the RV630 and M56 GPUs and was released freely to the public without any Non-Disclosure Agreement! However, they still have much more GPU documentation that has yet to be released.
The article goes on to mention that planning for open source 3D support is underway.