$ ls boot config-5.15.2 lost+found System.map-5.15.2 vmlinuz-5.15.2
$ ls config-5.1.21 lost+found System.map-5.1.21 uImage uImage-5.1.21
sudo mkimage -A arm -O linux -T kernel -C none -a 80008000 -e 80008000 -n kernel -d vmlinuz-5.15.2 uImage-5.15.2
sudo mkimage -A arm -O linux -T kernel -C gzip -a 80008000 -e 80008000 -n kernel -d vmlinuz-5.15.2 uImage-5.15.2