U-Boot with direct NVMe boot support for eMMC/SPI Flash

[Arwen]

...
to do that I can (basically) just copy most of the root over to the NVMe and change the fstab - simple enough?

Yes, basically you copy all "/" to the NVMe, change it's "/etc/fstab" to reflect the new location.
And then change "/boot/x/y" to reflect the new root location on the kernel command line. Like;

linux  /linux-5.4.72-gentoo.3 root=/dev/nvme0n1p1 ...

I've left off the exact path to the U-Boot config file, (the "x/y"), as I don't have that information handy.
Further, some distros keep the master U-Boot config file on "/etc/" somewhere, so "/boot/x/y" might get over-written on OS update.

If that does not work and you need to restore, simply boot off a SD card, (which you should make sure you have both a working one and that U-Boot recognizes it as boot target). Then modify the eMMC's "/boot/x/y" again, but restore the old until you can figure out what went wrong.

I can't give exact steps as I've not done it. But others have.


My suggestion is to come up with the steps first, including the back out plan. Then implement. If something goes wrong, you at least have a plan you can update with any missing step.