The latest NVIDIA Tegra 2D patches were published on Wednesday by Terje Bergstrom and can currently be found on the kernel mailing list. These patches are currently up to their seventh revision.
The set of 10 kernel patches introduce the host1x driver and 2D support. As far as the "host1x" component on the NVIDIA Tegra hardware, it's "the driver that controls host1x hardware. It supports host1x command channels, synchronization, and memory management."
The patch-set enables host1x and the 2D driver for the earlier-merged "tegradrm" driver. User-space interfaces are exposed by the patches for host1x and 2D so that an accelerated X.Org driver can be implemented around it.
The Tegra DRM driver work is being done by the community and other interested stakeholders with the official backing of NVIDIA -- read The Back Story On The Open NVIDIA Tegra Driver.
For more information on the state of the open-source NVIDIA Tegra graphics driver, see Open-Source NVIDIA Tegra Becoming More Exciting and NVIDIA Open-Source Tegra Driver Gets Enhanced. Hopefully the Tegra 2D support will be merged for the Linux 3.10 kernel and that NVIDIA Tegra 4 enablement on the open-source graphics stack isn't too far behind.
Sadly there's been no word by NVIDIA or the developers about any 3D/OpenGL ES support on the open-source Tegra stack. This though is a bit unlikely to see or hope for in the near-term.