Reboot to UEFI firmware settings from UEFI Shell

reset -c -fwui

There, you have it.

Adding EDK2 as a submodule without cloning it

Yeah, I have my reasons for this (mostly I commit on Windows, run the builds through GitHub Actions but compile from a non version-controlled Linux, and I don't want to suffer the wastage of yet another lengthy and cumbersome clone of EDK2).

This is mostly taken from https://stackoverflow.com/a/37378302/1069307:

mkdir edk2
git update-index --add --cacheinfo 160000 b158dad150bf02879668f72ce306445250838201 edk2
cat <<EOF >>.gitmodules
[submodule "edk2"]
	path = edk2
	url = https://github.com/tianocore/edk2.git
EOF

Of course, you should replace the commit hash with whatever current or stable EDK2 commit hash you want to point to.

And with this, you'll have added EDK2 as a submodule of your project without going through a cumbersome clone.