U-Boot on SPI flash - discussion

[Arwen]

If the new U-Boot image fails in such a way we can't work around the problems easily, we install a SD card that has a special signature our stage 1 code recognizes. If stage 1 sees this, it changes the U-Boot image selection to the other one, (aka old U-Boot image), and proceeds to boot.

Discussion anyone?

I would suggest if the stage 1 code recognizes an SD then it boots from that.  It seems more robust than looking for a special signature, and doesn't require an SD that has a special signature, or a working boot image on the SPI.

We already have that, nothing to be added. Any bootable SD card installed during power on / reset will cause the eMMC U-Boot to transfer booting to the SD card. That was an update to U-Boot a few weeks ago. We would then use the SD card's OS to fix the U-Boot of the eMMC.

My thought was allow continuing to boot to the eMMC or NVMe. Fix it from there, which may have the tools and U-Boot images. Of course, if we booted from SD card, we can mount an eMMC or NVMe file system, and get access to the tools & U-Boot images.

Perhaps something simpler. If the SPI stage 1 sees a bootable SD card, boot off it. If the SPI stage 1 sees a non-bootable SD card, then try the alternate SPI U-Boot image. That gets us the simplicity you were looking for, and fault tolerance I was looking for.