In message 9BB2AECBBDD3E6499663C42C1DFD40AAE496C5@PETWM02.calix.local you wrote:

I am trying to see if u-boot allows to have a single partition for both kernel and file system in NAND Flash.

Yes, you can do this. If it makes sense, depends on a lot of factors. Usually it does not.

Currently, I am looking at two possible approaches:

1. add an extra partition in the NAND flash and keep the second kernel

in there and have some way in u-boot to decide which one to load.

That's the standard approach and works just fine, even in fancy setups like bootcnt triggered automatic fallback scenarios. It's simple, and fast.

2. if u-boot allows, have one single partition for both kernel and file

system and upload both kernel images and have a soft link to a kernel image.

I'm not sure if the softlink idea works, but you can just switch the image filename in U-Boot. Works well, too, but is one of the slowest ways to boot a system.

I can't find a way to do the second option above, but that would be

Why not? It's a two-step procedure: first load the image to RAM, then bootm it...

ideal for field upgrade. Has anyone tried either of these approaches or have any other idea of how to do this? I am new to using u-boot and linux.

I tend to disagree that it's "ideal". But it can be done.

Best regards,

Wolfgang Denk