Tegra3 aka Surface RT Tegra4 aka Surface RT2
Good for reference DTB's etc
UBoot has Tegra Mainline support:
The ContextSwitcher switches back from the windows Bootmgr environment back to the UEFI environment. Good for patch reference for SurfaceRT Grub2 display. Also setup for VisualC
A prepatched GRUB2 ready for SurfaceRT or SurfaceRT2.
I'd also recommend reading Jay Carlson's excellent notes on Embedded Linux here - as an overview.
