[U-Boot] Raspberry Pi's MAC address locked to the first device the SD card boots on

[Timothy Froehlich]

We've had a problem the past few days that we've traced back to U-Boot.
We're generating images using Yocto with Mender's update routine. The issue
is the first time a clean image is booted on a Raspberry Pi, the mac
address gets permanently saved to the ethaddr env variable. It's a
combination of this line:

https://github.com/u-boot/u-boot/blob/b4ee6daad7a2604ca9466b2ba48de86cc27d381f/board/raspberrypi/rpi/rpi.c#L348

and what I'm pretty sure is Mender doing a "saveenv" on first boot. If you
move the SD card to a different Raspberry Pi, it will boot up with the mac
address of the first Raspberry Pi.

I'm not sure what the best long-term solution will be but I can make a
patch for my purposes to just always set ethaddr to usbethaddr.

So I guess i'm emailing this in to report an issue and maybe help anyone
else who runs into this issue.

-- 
Tim Froehlich
Embedded Linux Engineer
tfroehlich at archsys.io
215-218-8955