On Tue, Feb 20, 2018 at 6:19 AM, Baruch Siach [off-list ref] wrote:

The Raspberry Pi 3 GPIO expander is controlled by the VC4 firmware over
I2C. The firmware mailbox interface allows the ARM core to control the
GPIO lines.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
---
v5:
  * Remove the 'firmware' property
  * Note that the gpio node is a child of the firmware node

v4:
  * Move the example gpio node under the firmware node
  * Rename gpio node name to plain 'gpio'

v3:
  * Rename node name.

v2:
  * Rename compatible string to raspberrypi,firmware-gpio
---
 .../bindings/gpio/raspberrypi,firmware-gpio.txt    | 30 ++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/gpio/raspberrypi,firmware-gpio.txt

Reviewed-by: Rob Herring <robh@kernel.org>