This PDF document is available from AMD's developer area and is entitled "Evergreen Family Instruction Set Architecture - Instructions and Microcode." This documentation that covers their very latest GPUs in the Radeon HD 5000 series (like the Radeon HD 5750 and Radeon HD 5770) is important since its required for having the knowledge to provide 2D, 3D, and video acceleration for these newest Radeon graphics cards in the open-source Linux driver. This amounts to 362 pages of documentation that was just publicly released.
In regards to the open-source status for the ATI Radeon HD 5000 series graphics cards, with AMD's internal open-source code-base they do have VGA outputs continuing to work with these Evergreen GPUs, but digital outputs continue to be troublesome -- though they are making process. AMD's John Bridgman shared in our forums that this initial mode-setting code still needs to go through their internal review process but hopefully by the end of January the first code will be pushed out.