buildroot/target/initramfs/Config.in

config BR2_TARGET_ROOTFS_INITRAMFS
	bool "initramfs for initial ramdisk of linux kernel"
	default n
	help
	  Build a file which is usable for the gen_init_cpio tool
	  at linux kernel build. 
	  This file is normally called initramfs_list and can be
	  generated with gen_initramfs_list.sh script from the root
	  directory structure. 
	  The file is then used in the kernel build process to generate
	  the cpio filesystem for the initial ramdisk. Make sure that
	  you configure this file in kernel build configuration.
	  The location in the kernel build configuration menu is
	  Device Drivers -> Block devices -> Initramfs source file(s).
	  The configuration variable is CONFIG_INITRAMFS_SOURCE