Last week I wrote that compute support for AMD Evergreen (Radeon HD 5000 series) had landed and the latest Mesa Git commits from Wednesday afternoon now provide the "Cayman" support.
When you pair this latest code with a Radeon HD 6900 series graphics card, the OpenCL Clover Gallium3D state tracker (also in Mesa Git master now), LLVM 3.1, libclc, and build it all correctly, it should be possible to get basic OpenCL/GPGPU demos running off an open-source driver stack. It's still not quite a pleasant "out of the box" experience for end-users, but we're moving closer to open-source OpenCL support under Linux becoming viable.
It's been an active target for a long while -- the Clover state tracker has been talked about on Phoronix since summer of 2009 -- while three years later all of the pieces are finally coming together.
The commit that does the Cayman compute magic is 0c4b19, which will be part of Mesa 8.1.