My other meta question seems to have yet again brought to the fore the question of what is and isn't embedded programming. In other words, where the cutoff is for a questions being off-topic here and better moved to SO.
The current help article says that "the writing of firmware for bare-metal or RTOS applications" is on-topic, while "Programming software for a PC" is not. Personally, I understand "Programming software for a PC" to mean userspace.
This leaves the question whether kernel-space programming, and drivers specifically, are on topic on this site. Where exactly is the line?