An ADC is often used to measure other quantities indirectly. These
bindings describe two cases, a current through a sense resistor, and
a "big" voltage measured with the help of a voltage divider.

Signed-off-by: Peter Rosin <p...@axentia.se>
---
 .../bindings/iio/afe/current-sense-circuit.txt     | 45 ++++++++++++++++++++++
 .../bindings/iio/afe/voltage-divider.txt           | 45 ++++++++++++++++++++++
 MAINTAINERS                                        |  7 ++++
 3 files changed, 97 insertions(+)
 create mode 100644 
Documentation/devicetree/bindings/iio/afe/current-sense-circuit.txt
 create mode 100644 
Documentation/devicetree/bindings/iio/afe/voltage-divider.txt

diff --git 
a/Documentation/devicetree/bindings/iio/afe/current-sense-circuit.txt 
b/Documentation/devicetree/bindings/iio/afe/current-sense-circuit.txt
new file mode 100644
index 000000000000..0bc7d89387c0
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/afe/current-sense-circuit.txt
@@ -0,0 +1,45 @@
+Current Sense Curcuit
+=====================
+
+When an io-channel measures the voltage over a current sense resistor,
+the interesting mesaurement is often the current through the resistor,
+not the voltage over it. This binding describes such a current sense
+curcuit.
+
+Required properties:
+- compatible : "current-sense-circuit"
+- io-channels : Channel node of a voltage io-channel.
+
+Optional properties:
+- numerator : The io-channel scale is multiplied by this value (default 1).
+- denominator : The io-channel scale is divided by this value (default 1).
+
+Example:
+The system current is measured by measuring the voltage over a
+3.3 ohms sense resistor.
+
+sysi {
+       compatible = "current-sense-circuit";
+       io-channels = <&tiadc 0>;
+
+       /* Divide the ADC voltage by 33/10 (i.e. 3.3) to get the current. */
+       numerator = <10>;
+       denominator = <33>;
+};
+
+&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>;
+               };
+       };
+};
diff --git a/Documentation/devicetree/bindings/iio/afe/voltage-divider.txt 
b/Documentation/devicetree/bindings/iio/afe/voltage-divider.txt
new file mode 100644
index 000000000000..fd4a215d9e6d
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/afe/voltage-divider.txt
@@ -0,0 +1,45 @@
+Voltage divider
+===============
+
+When an io-channel measures the midpoint of a voltage divider, the
+interesting voltage is often the voltage over the full resistance
+of the divider. This binding describes the voltage divider in such
+a curcuit.
+
+Required properties:
+- compatible : "voltage-divider"
+- io-channels : Channel node of a voltage io-channel.
+
+Optional properties:
+- numerator : The io-channel scale is multiplied by this value (default 1).
+- denominator : The io-channel scale is divided by this value (default 1).
+
+Example:
+The system voltage is circa 12V, but divided down with a 22/200
+voltage divider to adjust it to the ADC range.
+
+SYSV        ADC       GND
+  +          +         +
+  |  .-----. | .----.  |
+  '--| 200 |-+-| 22 |--'
+     '-----'   '----'
+
+sysv {
+       compatible = "voltage-divider";
+       io-channels = <&maxadc 1>;
+
+       /* Multiply the ADC voltage by 222/22 to get the system voltage. */
+       numerator = <222>; /* 200 + 22 */
+       denominator = <22>;
+};
+
+&spi {
+       maxadc: adc@0 {
+               compatible = "maxim,max1027";
+               reg = <0>;
+               #io-channel-cells = <1>;
+               interrupt-parent = <&gpio5>;
+               interrupts = <15 IRQ_TYPE_EDGE_RISING>;
+               spi-max-frequency = <1000000>;
+       };
+};
diff --git a/MAINTAINERS b/MAINTAINERS
index 36a28e979e9a..9dbe5019c6bd 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6889,6 +6889,13 @@ F:       drivers/staging/iio/
 F:     include/linux/iio/
 F:     tools/iio/
 
+IIO UNIT CONVERTER
+M:     Peter Rosin <p...@axentia.se>
+L:     linux-...@vger.kernel.org
+S:     Maintained
+F:     Documentation/devicetree/bindings/iio/afe/current-sense-circuit.txt
+F:     Documentation/devicetree/bindings/iio/afe/voltage-divider.txt
+
 IKANOS/ADI EAGLE ADSL USB DRIVER
 M:     Matthieu Castet <castet.matth...@free.fr>
 M:     Stanislaw Gruszka <stf...@wp.pl>
-- 
2.11.0

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