Makefile: where does 'u-boot-dtb.imx' come from?

[iam-TJ]

I'm currently writing a new Makefile that instead of needing to do network fetches each time uses locally git clone-d repositories. In reading through the current file to ensure I understand what build products are required and I see:

usbarmory-${IMG_VERSION}.raw.xz: usbarmory-${IMG_VERSION}.raw u-boot-${UBOOT_VER}/u-boot.bin
  sudo dd if=u-boot-${UBOOT_VER}/u-boot-dtb.imx of=usbarmory-${IMG_VERSION}.raw bs=512 seek=2 conv=fsync conv=notrunc
  xz -k usbarmory-${IMG_VERSION}.raw

But I cannot see where or how u-boot-dtb.imx is obtained or created. There is no mention of it elsewhere in the project or in any of the other repositories save one related to Secure Boot:

$ grep -rn u-boot-dtb
usbarmory-debian-base_image/Makefile:176:       sudo dd if=u-boot-${UBOOT_VER}/u-boot-dtb.imx of=usbarmory-${IMG_VERSION}.raw bs=512 seek=2 conv=fsync conv=notrunc
usbarmory/software/secure_boot/mark-one/hab4.csf:41:  Blocks = 0x777FF400 0x0 0x49C00 "/tmp/u-boot-dtb.imx"

[iam-TJ]

Answering my own question - I wasn't looking in the correct location!

$ grep -rn u-boot-dtb.imx ../bootloaders/u-boot/u-boot/
../bootloaders/u-boot/u-boot/arch/arm/config.mk:168:INPUTS-y += u-boot-dtb.imx