Hi! I’m also relatively new to Yocto and Mender, so this may not be an optimal solution, but it’s working for us.
In my meta-myproject layer I created a recipes-bsp/ directory containing these files:
./u-boot/u-boot_%.bbappend:
FILESEXTRAPATHS_prepend := "${THISDIR}/files:"
SRC_URI_append += "file://no_config_env_is_in_fat.cfg"
This is a relatively simple bbappend file that adds the ./files/ directory to the search path, and then tells the recipe to include the new no_config_env_is_in_fat.cfg file, which it somehow knows is a config file (maybe it assumes that for .cfg files, maybe it parses the file, I’m not sure).
./u-boot/files/no_config_env_is_in_fat.cfg:
CONFIG_ENV_IS_IN_FAT=n
This KCONF snippet changes the compilation options for u-boot, to disable support for storing the env in fat.
Hope that helps!