iio: Add Nuvoton NAU7802 ADC driver

The Nuvoton NAU7802 ADC is a 24-bit 2-channels I2C ADC, with adjustable
gain and sampling rates.
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/nuvoton-nau7802.txt

+* Nuvoton NAU7802 Analog to Digital Converter (ADC)
+
+Required properties:
+  - compatible: Should be "nuvoton,nau7802"
+  - reg: Should contain the ADC I2C address
+
+Optional properties:
+  - nuvoton,vldo: Internal reference voltage in millivolts to be
+    configured valid values are between 2400 mV and 4500 mV.
+  - interrupts: IRQ line for the ADC. If not used the driver will use
+    polling.
+
+Example:
+adc2: nau7802@2a {
+	compatible = "nuvoton,nau7802";
+	reg = <0x2a>;
+	nuvoton,vldo = <3000>;
+};

drivers/iio/adc/Kconfig

@@ -143,6 +143,15 @@ config MCP320X
 	  This driver can also be built as a module. If so, the module will be
 	  called mcp320x.
 
+config NAU7802
+	tristate "Nuvoton NAU7802 ADC driver"
+	depends on I2C
+	help
+	  Say yes here to build support for Nuvoton NAU7802 ADC.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called nau7802.
+
 config TI_ADC081C
 	tristate "Texas Instruments ADC081C021/027"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -15,6 +15,7 @@ obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o
 obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
 obj-$(CONFIG_MAX1363) += max1363.o
 obj-$(CONFIG_MCP320X) += mcp320x.o
+obj-$(CONFIG_NAU7802) += nau7802.o
 obj-$(CONFIG_TI_ADC081C) += ti-adc081c.o
 obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o
 obj-$(CONFIG_VIPERBOARD_ADC) += viperboard_adc.o