While the reverse-engineered Nouveau graphics driver has limited support for OpenCL/GPGPU support, it's been mainly capped to older "NV50" graphics cards. Published today though for review are patches for the Fermi "NVC0" hardware to expose compute support as well as the hardware performance counters.
Samuel Pitoiset, working on the Nouveau driver as a GSoC project, added NVC0 compute support as needed for exposing the MP performance counters on NVIDIA GeForce 400/500 "Fermi" graphics cards. A 716 line patch
adds in the Gallium3D compute support by leveraging the existing Gallium3D compute infrastructure. The support is basically the ability to launch a compute kernel with Nouveau on this more recent NVIDIA GeForce architecture.
Before getting too excited though, this is just very basic compute support and will not be really useful yet for end-users. The code is also under an "RFC" (Request For Comments) flag and will likely go through a few revisions before being merged into mainline Mesa, which might not happen until after Mesa 9.2 has been branched.
His second patch
implements MP performance counters for NVC0 to NVC8. The NVC8 hardware is the GeForce GTX 560/570/580/590. This patch is just 440 lines of new code.
More details on the Nouveau/NVIDIA performance counter exploration can be found via Samuel Pitoiset's blog