Comment # 12 on bug 1002194 from Freek de Kruijf

I connected the USB serial cable to the RPi3 and managed to get the U-Boot
prompt. I followed the menu to use setenv and entered the command "boot usb0".
This did not do what was expected. I used some other U-Boot commands; did see a
connected USB disk with the ISO image on it listed. However a connected USB
stick with the ISO image on it was not listed. U-Boot did not see that device.
After all I could NOT boot from the USB ISO disk.

I tried to find some information about support for ISO type disks, seems to
depend on conditional compilation settings. I could not find if these are set
to support ISO type disks.