1Raspberry Pi GPIO expander 2 3The Raspberry Pi 3 GPIO expander is controlled by the VC4 firmware. The 4firmware exposes a mailbox interface that allows the ARM core to control the 5GPIO lines on the expander. 6 7The Raspberry Pi GPIO expander node must be a child node of the Raspberry Pi 8firmware node. 9 10Required properties: 11 12- compatible : Should be "raspberrypi,firmware-gpio" 13- gpio-controller : Marks the device node as a gpio controller 14- #gpio-cells : Should be two. The first cell is the pin number, and 15 the second cell is used to specify the gpio polarity: 16 0 = active high 17 1 = active low 18 19Example: 20 21firmware: firmware-rpi { 22 compatible = "raspberrypi,bcm2835-firmware"; 23 mboxes = <&mailbox>; 24 25 expgpio: gpio { 26 compatible = "raspberrypi,firmware-gpio"; 27 gpio-controller; 28 #gpio-cells = <2>; 29 }; 30}; 31