dt-bindings: iio: afe: add binding for current-sense-shunt

An ADC is often used to measure other quantities indirectly. This
binding describe one cases, a current through a shunt resistor
measured by the voltage over it.
Signed-off-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/afe/current-sense-shunt.txt

+Current Sense Shunt
+===================
+
+When an io-channel measures the voltage over a current sense shunt,
+the interesting mesaurement is almost always the current through the
+shunt, not the voltage over it. This binding describes such a current
+sense circuit.
+
+Required properties:
+- compatible : "current-sense-shunt"
+- io-channels : Channel node of a voltage io-channel.
+- shunt-resistor-micro-ohms : The shunt resistance in microohms.
+
+Example:
+The system current is measured by measuring the voltage over a
+3.3 ohms shunt resistor.
+
+sysi {
+	compatible = "current-sense-shunt";
+	io-channels = <&tiadc 0>;
+
+	/* Divide the voltage by 3300000/1000000 (or 3.3) for the current. */
+	shunt-resistor-micro-ohms = <3300000>;
+};
+
+&i2c {
+	tiadc: adc@48 {
+		compatible = "ti,ads1015";
+		reg = <0x48>;
+		#io-channel-cells = <1>;
+
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		channel@0 { /* IN0,IN1 differential */
+			reg = <0>;
+			ti,gain = <1>;
+			ti,datarate = <4>;
+		};
+	};
+};

MAINTAINERS

@@ -6898,6 +6898,12 @@ F:	drivers/staging/iio/
 F:	include/linux/iio/
 F:	tools/iio/
 
+IIO UNIT CONVERTER
+M:	Peter Rosin <peda@axentia.se>
+L:	linux-iio@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/iio/afe/current-sense-shunt.txt
+
 IKANOS/ADI EAGLE ADSL USB DRIVER
 M:	Matthieu Castet <castet.matthieu@free.fr>
 M:	Stanislaw Gruszka <stf_xl@wp.pl>