Interesting Repo's

Nvidia Linux files

https://developer.nvidia.com/linux-tegra-rel-16 Tegra3 aka Surface RT https://developer.nvidia.com/linux-tegra-rel-17 Tegra4 aka Surface RT2

UBOOT Tegra

Good for reference DTB's etc https://github.com/OE4T/u-boot-tegra

UBoot has Tegra Mainline support: https://gitlab.denx.de/u-boot/u-boot

Context Switcher for Tegra3

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 https://github.com/imbushuo/boot-shim-tegra-3

QEMU for ARM32

https://designprincipia.com/virtualize-uefi-on-arm-using-qemu/

Fusee Gelee for T30 (Surface RT)

GitHub - jevinskie/fusee-launcher at b6e03fd7042ba2f1c989c1d007ebee6d4b5165efGitHub

GitHub - tofurky/tegra30_debrick: fusee-gelee payload, supporting files, and guide for debricking Tegra 3 devices (2012 Nexus 7 and Ouya)GitHub

GRUB BootLoader

A prepatched GRUB2 ready for SurfaceRT or SurfaceRT2. https://github.com/coherixmatts/grub-2.04

Misc

How the ARM32 kernel starts — linuswlinusw

I'd also recommend reading Jay Carlson's excellent notes on Embedded Linux here - https://jaycarlson.net/embedded-linux/ as an overview.