[PATCH 1/7] Documentation: DT: bindings: iio: adc: add documentation for Allwinner SoCs' GPADC driver

The Allwinner SoCs all have an ADC that can also act as a thermal sensor
and sometimes as a touchscreen controller. If there is a touchscreen
controller, the first four channels can be used either for the ADC or
the touchscreen and the fifth channel is used for the thermal sensor.
If there is not a touchscreen controller, the one and only channel is
used for the thermal sensor.

This patch adds the documentation for the driver of the Allwinner SoCs'
GPADC.

Signed-off-by: Quentin Schulz <redacted>
---
 .../bindings/iio/adc/sun4i-gpadc-iio.txt           | 57 ++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/adc/sun4i-gpadc-iio.txt

diff --git a/Documentation/devicetree/bindings/iio/adc/sun4i-gpadc-iio.txt b/Documentation/devicetree/bindings/iio/adc/sun4i-gpadc-iio.txt
new file mode 100644
index 0000000..aab768d
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/adc/sun4i-gpadc-iio.txt

@@ -0,0 +1,57 @@
+Allwinner SoCs' GPADC Device Tree bindings
+------------------------------------------
+
+The Allwinner SoCs all have an ADC that can also act as a thermal sensor and
+sometimes as a touchscreen controller. If there is a touchscreen controller, the
+first four channels can be used either for the ADC or the touchscreen and the
+fifth channel is used for the thermal sensor.
+If there is not a touchscreen controller, the one and only channel is used for
+the thermal sensor.
+
+Currently, the touchscreen controller does not have a driver using this ADC
+driver. The touchscreen controller is currently driven only by
+input/touchscreen/sun4i-ts.c which is absolutely incompatible with this driver.
+
+The Allwinner A10, A13 and A31 SoCs already have a DT binding for the
+aforementioned input driver, thus an MFD driver matches the existing DT binding
+(mfd/sun4i-gpadc.c) and replaces the input driver. No DT binding is required for
+these SoCs' ADC, everything is handled by the MFD which is matching the existing
+DT binding for input/touchscreen/sun4i-ts.c.
+
+The Allwinner A33 GPADC only have a thermal sensor and have a proper DT binding
+for this driver unlike the previously mentioned SoCs.

+
+Optional properties:
+(for use with thermal framework for CPU thermal throttling for example, and/or
+ IIO consumers)
+ - #thermal-sensor-cells = <0>; (see
+Documentation/devicetree/bindings/thermal/thermal.txt)
+ - #io-channel-cells = <0>; (see
+Documentation/devicetree/bindings/iio/iio-bindings.txt)