Allow linear scaling and modification of the type of an io-channel.
When an ADC channel measures the midpoint of a voltage divider, the
interesting voltage is often the voltage over the full resistance
of the divider. Likewise, measuring the voltage over a resistor is
often a way to get to the current through it.
This binding allows description of such hardware which is external
to the ADC.
Signed-off-by: Peter Rosin <peda@xxxxxxxxxx>
---
.../iio/wrapper/io-channel-unit-converter.txt | 84 ++++++++++++++++++++++
MAINTAINERS | 6 ++
2 files changed, 90 insertions(+)
create mode 100644 Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
diff --git a/Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt b/Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
new file mode 100644
index 000000000000..23af661abe32
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
@@ -0,0 +1,84 @@
+I/O channel unit converter bindings
+
+Allow linear scaling and modification of the type of an io-channel.
+
+When an ADC channel measures the midpoint of a voltage divider, the
+interesting voltage is often the voltage over the full resistance
+of the divider. Likewise, measuring the voltage over a resistor is
+often a way to get to the current through it.
+
+Required properties:
+- compatible : "io-channel-unit-converter"
+- io-channels : Channel node of the parent channel.
+- io-channel-names : Should be "parent".
+
+Optional properties:
+- numerator : The parent channel scale is multiplied by this value (default 1).
+- denominator : The parent channel scale is divided by this value (default 1).
+- type : The type of the wrapped channel is modified to this type. The default
+ is to use the same type as the parent channel. Recognized types are:
+ "voltage"
+ "current"
+
+Example 1:
+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 = "io-channel-unit-converter";
+ io-channles = <&maxadc 1>;
+ io-channel-names = "parent";
+
+ /* 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>;
+ };
+};
+
+Example 2:
+The system current is measured by measuring the voltage over a
+3.3 ohm resistor.
+
+sysi {
+ compatible = "io-channel-unit-converter";
+ io-channles = <&tiadc 0>;
+ io-channel-names = "parent";
+
+ /* divide the ADC voltage by 33/10 (i.e. 3.3) to get current */
+ numerator = <10>;
+ denominator = <33>;
+ type = "current";
+}
+
+&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/MAINTAINERS b/MAINTAINERS
index 96e5503bfb60..5dd555c7b1b0 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -6884,6 +6884,12 @@ F: drivers/staging/iio/
F: include/linux/iio/
F: tools/iio/
+IIO UNIT CONVERTER
+M: Peter Rosin <peda@xxxxxxxxxx>
+L: linux-iio@xxxxxxxxxxxxxxx
+S: Maintained
+F: Documentation/devicetree/bindings/iio/wrapper/io-channel-unit-converter.txt
+
IKANOS/ADI EAGLE ADSL USB DRIVER
M: Matthieu Castet <castet.matthieu@xxxxxxx>
M: Stanislaw Gruszka <stf_xl@xxxxx>
--
2.11.0
--
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