The patches were merged last night into the Nouveau DRM development tree for enabling Pascal hardware acceleration for the GP102 to GP107 Pascal GPUs. We should be seeing the binary firmware release to pair with the driver today. While this is a huge milestone and great to see it finally happen, do note this initial support doesn't yet have any re-clocking (similar to the Maxwell Nouveau support) and is basically in the same boat as Maxwell in terms of supported features, etc.
Kernel mode-setting has been supported for a few kernel cycles now with Pascal GPUs while the acceleration was held up by NVIDIA with their signed firmware images and necessary DRM code changes for supporting the new blobs. The code is staged in the skeggsb/nouveau branch. Sadly this code is coming just too late for making the Linux 4.11 merge window, so this support likely won't be merged until Linux 4.12. While there isn't much to be expected in the way of performance until re-clocking support comes, I'll run some Pascal 3D Nouveau tests in the near future.