I'm not advocating for secure boot. In fact I advocate against any form of secure boot that is not under the user control at all times.
Yes, we agree violently ;-)
Yes. I only said that because SD cards have a switch and uSD cards don't so I thought there is some mechanical difficulty in puting a switch in a card so small.
Oh, you're right, I forgot that µSD cards don't have the little advisory switch. So we'd need an SD card instead. I can live with it.
You could put a switch in a uSD card, but that would make the whole uSD card read only, so you would need something else for storage space. If you can get simply a part readonly that'd be much better and self contained.
Sure, you can always ask for more, but since the A20 comes with plenty of MMC ports, you can have a whole read-only SD card plus a separate read-write µSD card.
Stefan "whose Orange Pi mini has 2 µSD slots one of which holds a card with nothing else than U-boot"