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Raspberry Pi GPIO expander
The Raspberry Pi 3 GPIO expander is controlled by the VC4 firmware. The
firmware exposes a mailbox interface that allows the ARM core to control the
GPIO lines on the expander.
The Raspberry Pi GPIO expander node must be a child node of the Raspberry Pi
firmware node.
Required properties:
- compatible : Should be "raspberrypi,firmware-gpio"
- gpio-controller : Marks the device node as a gpio controller
- #gpio-cells : Should be two. The first cell is the pin number, and
the second cell is used to specify the gpio polarity:
0 = active high
1 = active low
firmware: firmware-rpi {
compatible = "raspberrypi,bcm2835-firmware";
mboxes = <&mailbox>;
expgpio: gpio {
compatible = "raspberrypi,firmware-gpio";
#gpio-cells = <2>;