Lucas Stach of the Nouveau project just finished speaking at XDC2012 Nürnberg about open-source Tegra support. Lucas is one of the developers that as of late that have been toying around with open-source NVIDIA Tegra support.
Linus Torvalds called NVIDIA the worst company ever with the now popularized "fuck you" remark joined by his middle finger.
Up to this point NVIDIA hasn't exactly been open-source friendly with not providing any documentation and also not supporting the Nouveau open-source driver project. Their official stance is that they will not do anything to help nor hinder Nouveau.
Recently, however, there's seemingly been an interesting change of attitude with Nouveau having some same-day support since two developers managed to somehow get their hands on GeForce GTX 680 graphics cards early. Early GK110 support is also underway. Don't be surprised if you see more NVIDIA support going forward in some subtle ways.
It was also heard a few months back that NVIDIA was looking at Wayland support for Tegra based upon customer feedback, although nothing in that areas has officially materialized in the public spotlight. A Tegra DRM driver is started and there's also been some reverse-engineering of the 3D Tegra support.
In quickly asking Ritger about the forthcoming graphics documentation, he mentions that he's been told the next version of the Tegra TRM (Technical Reference Manual) should provide the public with this (NDA-free) documentation covering the 2D engine. This information should be effectively the same for the Tegra 2 and Tegra 3 generations. He officially hasn't been told anything concerning public 3D documentation. Andy also didn't make any statements concerning documentation for their GeForce/Quadro GPUs.
Times look to be changing. The video of this XDC2012 presentation will be available shortly. It was five years ago to the month that AMD announced their open-source Linux graphics strategy.
Meanwhile, no other ARM SoCs were brought up at during XDC2012 aside from some brief Freedreno mentions. The Lima driver was not mentioned although Luc was in attendance.
Update: Here's the video of the Tegra presentation at XDC2012.