This explains how to create a firmware for an unsupported device you have. For example, D-Link DIR-816 A1
To get a minimal list of files required to add a new board use this command:
#grep -lri DIR816-A1 target/
the list of files will be like:
target/linux/ramips/image/mt7620.mk
target/linux/ramips/dts/dir-816-A1.dts
target/linux/ramips/base-files/lib/ramips.sh
target/linux/ramips/base-files/lib/upgrade/platform.sh
target/linux/ramips/base-files/etc/board.d/02_network
target/linux/ramips/base-files/etc/board.d/01_leds
Edit these files to get the required configuration.
use this command to reset the make file:
touch target/linux/*/Makefile