1. How uboot changes to the new partition when kernel fails to start.
2. kernel changes any boot arguments to notify the uboot ?
For roll back to another kernel in case of failure/crash of current kernel, you can do below things(just a raw idea):
1) Create two partition scheme both will have zImage and dtb.
2) Change the boot partition from u-boot. (change mmcdev and mmcpart env variables)
3) To automatically detect the kernel failure you can use the bootcount and bootlimit variables in u-boot and implement the mechanism to switch automatically.
For further understanding of the same in detail please refer to the SWUpdate: software update for embedded system — Embedded Software Update Documentation 2019.11 docum... .
Regards,
Radhika Somaiya.
Have you download images success to your board? Here you can send us your fail log.
Could you tell us which version of BSP are you using?