Recent VC4 firmware provides a hardware-independent way to retrieve the
under-voltage sensor on the following Raspberry Pi boards:
  - Raspberry Pi B+ (via GPIO on SoC)
  - Raspberry Pi A+ (via GPIO on SoC)
  - Raspberry Pi 2 B (via GPIO on SoC)
  - Raspberry Pi 3 B (via GPIO on port expander)
  - Raspberry Pi 3 B+ (via PMIC)

TODO:
  - try to make bcm2835 firmware a bus driver

Signed-off-by: Stefan Wahren <redacted>
---
 .../devicetree/bindings/hwmon/raspberrypi-hwmon.txt   | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/raspberrypi-hwmon.txt

diff --git a/Documentation/devicetree/bindings/hwmon/raspberrypi-hwmon.txt b/Documentation/devicetree/bindings/hwmon/raspberrypi-hwmon.txt
new file mode 100644
index 0000000..ec2523f
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/raspberrypi-hwmon.txt

@@ -0,0 +1,19 @@
+Raspberry Pi voltage sensor
+---------------------------
+
+The VC4 firmware exposes a mailbox interface that allows the ARM core
+to access the board's voltage sensor.
+
+Required properties :
+- compatible : Should be "raspberrypi,bcm2835-hwmon"
+
+Example:
+
+firmware: firmware-rpi {
+	compatible = "raspberrypi,bcm2835-firmware";
+	mboxes = <&mailbox>;
+
+	voltage-sensor {
+		compatible = "raspberrypi,bcm2835-hwmon";
+	};
+};

-- 
2.7.4