"sudo make modules_prepare" fails

We’re trying to build a custom kernel module and receive the below failure:

jetson-0423018055078# pwd

jetson-0423018055078# sudo make modules_prepare
scripts/kconfig/conf  --silentoldconfig Kconfig
arch/arm64/Kconfig:1221: can't open file "drivers/firmware/tegra/Kconfig"
scripts/kconfig/Makefile:37: recipe for target 'silentoldconfig' failed
make[2]: *** [silentoldconfig] Error 1
Makefile:562: recipe for target 'silentoldconfig' failed
make[1]: *** [silentoldconfig] Error 2
make: *** No rule to make target 'include/config/auto.conf', needed by 'include/config/kernel.release'.  Stop.

This is with latest Jetpack on the Xavier (4.0) with all options installed. Gcc version 7.3.0.

Any help would be most appreciated

Looks like you need to download the l4t kernel source and run that command in the source folder. The directory you are in is just the headers.