iio: chemical: add Atlas pH-SM sensor support

Add support for the Atlas Scientific pH-SM chemical sensor that can
detect pH levels of solutions in the range of 0-14.
Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/chemical/atlas,ph-sm.txt

+* Atlas Scientific pH-SM OEM sensor
+
+http://www.atlas-scientific.com/_files/_datasheets/_oem/pH_oem_datasheet.pdf
+
+Required properties:
+
+  - compatible: must be "atlas,ph-sm"
+  - reg: the I2C address of the sensor
+  - interrupt-parent: should be the phandle for the interrupt controller
+  - interrupts: the sole interrupt generated by the device
+
+  Refer to interrupt-controller/interrupts.txt for generic interrupt client
+  node bindings.
+
+Example:
+
+atlas@65 {
+	compatible = "atlas,ph-sm";
+	reg = <0x65>;
+	interrupt-parent = <&gpio1>;
+	interrupts = <16 2>;
+};

drivers/iio/chemical/Kconfig

@@ -4,6 +4,19 @@
 
 menu "Chemical Sensors"
 
+config ATLAS_PH_SENSOR
+	tristate "Atlas Scientific OEM pH-SM sensor"
+	depends on I2C
+	select REGMAP_I2C
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	 Say Y here to build I2C interface support for the Atlas
+	 Scientific OEM pH-SM sensor.
+
+	 To compile this driver as module, choose M here: the
+	 module will be called atlas-ph-sensor.
+
 config IAQCORE
 	tristate "AMS iAQ-Core VOC sensors"
 	depends on I2C

drivers/iio/chemical/Makefile

@@ -3,5 +3,6 @@
 #
 
 # When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_ATLAS_PH_SENSOR)	+= atlas-ph-sensor.o
 obj-$(CONFIG_IAQCORE)		+= ams-iaq-core.o
 obj-$(CONFIG_VZ89X)		+= vz89x.o