This news shouldn't be a complete surprise since for months we have known that NVIDIA has been working out some public documentation concerning the graphics on their ARM-based Tegra SoCs. There's 2D documentation on Tegra and potentially 3D documentation to be eventually released too for this embedded hardware, but sadly likely no change of course for their GeForce/Quadro architecture.
NVIDIA now contributing to this open-source Tegra DRM driver shouldn't be a big surprise either since they have already been helpful in the driver's initial development. Patches previously published such as for enabling the HDMI output support note the helpfulness of NVIDIA engineers on this open-source Linux graphics driver. "A lot of work on this patch has been contributed by NVIDIA's Mark Zhang and many other people at NVIDIA were very helpful in getting the HDMI support and surrounding infrastructure to work." That recent contribution was from mid-November.
Thierry Reding, the Linux developer initially working on the Tegra DRM driver, mentioned NVIDIA's imminent 2D contribution in a new mailing list post. "With tegra-drm going into Linux 3.8 and NVIDIA posting initial patches for 2D acceleration on top of it..."
Reding mentioned this in a mailing list post because he's deciding how to implement the DDX driver for Tegra with acceleration. He could write an xf86-video-tegra driver that could be a partial fork of the generic xf86-video-modesetting driver with the various Tegra-specific acceleration hooks applied, or he could come up with a more innovative approach. One of the options he's looking at is making improvements to the generic xf86-video-modesetting driver where GPU-specific acceleration could be applied on top and be leveraged by other drivers while sharing this common base.
Anyhow, look for more open-source graphics excitement in the coming months.