The 2D graphics acceleration support for NVIDIA Tegra 2 and Tegra 3 ARM SoCs is still maturing and going through code revisions before entering the mainline Linux kernel, hopefully for Linux 3.10.
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."