iio: potentiostat: add LMP91000 support

Add support for the LMP91000 potentiostat which is used for chemical
sensing applications.
Signed-off-by: Matt Ranostay <matt@ranostay.consulting>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/potentiostat/lmp91000.txt

+* Texas Instruments LMP91000 potentiostat
+
+http://www.ti.com/lit/ds/symlink/lmp91000.pdf
+
+Required properties:
+
+  - compatible: should be "ti,lmp91000"
+  - reg: the I2C address of the device
+  - io-channels: the phandle of the iio provider
+
+  - ti,external-tia-resistor: if the property ti,tia-gain-ohm is not defined this
+    needs to be set to signal that an external resistor value is being used.
+
+Optional properties:
+
+  - ti,tia-gain-ohm: ohm value of the internal resistor for the transimpedance
+    amplifier. Must be 2750, 3500, 7000, 14000, 35000, 120000, or 350000 ohms.
+
+  - ti,rload-ohm: ohm value of the internal resistor load applied to the gas
+    sensor. Must be 10, 33, 50, or 100 (default) ohms.
+
+Example:
+
+lmp91000@48 {
+	compatible = "ti,lmp91000";
+	reg = <0x48>;
+	ti,tia-gain-ohm = <7500>;
+	ti,rload = <100>;
+	io-channels = <&adc>;
+};

drivers/iio/Kconfig

@@ -87,6 +87,7 @@ if IIO_TRIGGER
    source "drivers/iio/trigger/Kconfig"
 endif #IIO_TRIGGER
 source "drivers/iio/potentiometer/Kconfig"
+source "drivers/iio/potentiostat/Kconfig"
 source "drivers/iio/pressure/Kconfig"
 source "drivers/iio/proximity/Kconfig"
 source "drivers/iio/temperature/Kconfig"

drivers/iio/Makefile

@@ -29,6 +29,7 @@ obj-y += light/
 obj-y += magnetometer/
 obj-y += orientation/
 obj-y += potentiometer/
+obj-y += potentiostat/
 obj-y += pressure/
 obj-y += proximity/
 obj-y += temperature/

drivers/iio/potentiostat/Kconfig

+#
+# Potentiostat drivers
+#
+# When adding new entries keep the list in alphabetical order
+
+menu "Digital potentiostats"
+
+config LMP91000
+	tristate "Texas Instruments LMP91000 potentiostat driver"
+	depends on I2C
+	select REGMAP_I2C
+	select IIO_BUFFER
+	select IIO_BUFFER_CB
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say yes here to build support for the Texas Instruments
+	  LMP91000 digital potentiostat chip.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called lmp91000
+
+endmenu

drivers/iio/potentiostat/Makefile

+#
+# Makefile for industrial I/O potentiostat drivers
+#
+
+# When adding new entries keep the list in alphabetical order
+obj-$(CONFIG_LMP91000) += lmp91000.o