Back in February we heard a goal of having OpenCL in Gallium3D by this summer and then in May we heard that it was hopefully soon along with an OpenGL 3.1 state tracker. Well, it's just about September and the summer is nearing an end, but we now have OpenCL support in the works.
Over on the FreeDesktop.org Git server is now a mesa/clover repository. This code repository contains Zack Rusin's work on adding an OpenCL implementation to Gallium3D. Right now, however, this code is still very incomplete and immature, but it's out there for those who are interested. It also shows that this support began in December of 2008, but it wasn't even worked on this year until starting eleven days ago.
This code is dependent upon LLVM (the Low-Level Virtual Machine) and its Clang compiler component. Of course, you will also need a working Gallium3D driver for your graphics card too.
Judging from this code it will still be a while before this OpenCL support on Linux is ready to enter the limelight, but at least it's coming.