Not strictly Blender-related, but it seems that the open-source Radeon drivers are getting closer to supporting OpenCL. Following these instructions got me some basic OpenCL on Ubuntu 12.04 with very little effort. The only issue I had was that libclc failed to link, had to add an extra “-ldl” to the Makefile. (Also, the list of dev packages I installed: xutils-dev x11proto-gl-dev x11proto-dri2-dev libx11-xcb-dev libxcb-glx0-dev libxcb-dri2-0-dev libxcb-xfixes0-dev libudev-dev bison).
This implementation of OpenCL is in the early stages and definitely won’t run Cycles yet (I tried, of course. The list of OpenCL devices does show my “AMD CAYMAN”, but attempting to render crashes with various OpenCL errors.) Still, very cool to see this progress being made.