[azzentys]

A lot of work here is working on vendor provided BSP (which can range from esoteric mix of ancient kernels/bootloaders to top-quality community maintained mainline kernels) to work on your custom board/product.

[pabs3]

So Linux kernel config/building/patching?

[afr0ck]

Linux kernel + bootloaders + firmware

The Linux kernel side is mostly device trees, device drivers and the like.

u-boot is very famous as a bootloader in the embedded space

Firmware for board bring up and devices