Work that landed in Mesa Git on Friday by Ilia Mirkin adds shader atomic counters support and shader storage buffer object (SSBO) support as needed by OpenGL 4.2 and 4.3, respectively. Nouveau NVC0 is the second driver after Intel's i965 classic code to support these extensions.
ARB_shader_storage_buffer_object allows shaders to perform random access read/writes and atomic memory operations on variables within a buffer object. ARB_shader_atomic_counters provides a set of atomic counters.
With Ilia Mirkin doing the heavy lifting by adding the atomic counters and SSBO support to the Mesa Gallium3D state tracker, hopefully it won't be long before the RadeonSI driver is also supporting these OpenGL 4.2/4.3 extensions. All NVC0 has left now until hitting OpenGL 4.2 compliance is tackling ARB_shader_image_load_store, which Mirkin is already working on (state tracker patches published, but the NVC0 implementation isn't yet ready) and will be covered in another Phoronix article shortly.