This chip is a popular way to add a matrix keyboard using I2C.
CONFIG_INPUT_EVDEV=y
# CONFIG_KEYBOARD_ATKBD is not set
CONFIG_KEYBOARD_GPIO=m
+CONFIG_KEYBOARD_TCA8418=m
CONFIG_KEYBOARD_MATRIX=m
CONFIG_KEYBOARD_CAP11XX=m
# CONFIG_INPUT_MOUSE is not set
CONFIG_INPUT_EVDEV=y
# CONFIG_KEYBOARD_ATKBD is not set
CONFIG_KEYBOARD_GPIO=m
+CONFIG_KEYBOARD_TCA8418=m
CONFIG_KEYBOARD_MATRIX=m
CONFIG_KEYBOARD_CAP11XX=m
# CONFIG_INPUT_MOUSE is not set
CONFIG_INPUT_EVDEV=y
# CONFIG_KEYBOARD_ATKBD is not set
CONFIG_KEYBOARD_GPIO=m
+CONFIG_KEYBOARD_TCA8418=m
CONFIG_KEYBOARD_MATRIX=m
CONFIG_KEYBOARD_CAP11XX=m
# CONFIG_INPUT_MOUSE is not set
CONFIG_INPUT_EVDEV=y
# CONFIG_KEYBOARD_ATKBD is not set
CONFIG_KEYBOARD_GPIO=m
+CONFIG_KEYBOARD_TCA8418=m
CONFIG_KEYBOARD_MATRIX=m
CONFIG_KEYBOARD_CAP11XX=m
# CONFIG_INPUT_MOUSE is not set
CONFIG_INPUT_EVDEV=y
# CONFIG_KEYBOARD_ATKBD is not set
CONFIG_KEYBOARD_GPIO=m
+CONFIG_KEYBOARD_TCA8418=m
CONFIG_KEYBOARD_MATRIX=m
CONFIG_KEYBOARD_CAP11XX=m
# CONFIG_INPUT_MOUSE is not set