iio: adc: add ADC12130/ADC12132/ADC12138 ADC driver

This adds Texas Instruments' ADC12130/ADC12132/ADC12138 12-bit plus
sign ADC driver.  I have tested with the ADC12138.  The ADC12130 and
ADC12132 are not tested but these are similar to ADC12138 except that
the mode programming instruction is a bit different.
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Hartmut Knaack <knaack.h@gmx.de>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Peter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/ti-adc12138.txt

+* Texas Instruments' ADC12130/ADC12132/ADC12138
+
+Required properties:
+ - compatible: Should be one of
+	* "ti,adc12130"
+	* "ti,adc12132"
+	* "ti,adc12138"
+ - reg: SPI chip select number for the device
+ - interrupts: Should contain interrupt for EOC (end of conversion)
+ - clocks: phandle to conversion clock input
+ - spi-max-frequency: Definision as per
+	Documentation/devicetree/bindings/spi/spi-bus.txt
+ - vref-p-supply: The regulator supply for positive analog voltage reference
+
+Optional properties:
+ - vref-n-supply: The regulator supply for negative analog voltage reference
+	(Note that this must not go below GND or exceed vref-p)
+	If not specified, this is assumed to be analog ground.
+ - ti,acquisition-time: The number of conversion clock periods for the S/H's
+	acquisition time.  Should be one of 6, 10, 18, 34.  If not specified,
+	default value of 10 is used.
+	For high source impedances, this value can be increased to 18 or 34.
+	For less ADC accuracy and/or slower CCLK frequencies this value may be
+	decreased to 6.  See section 6.0 INPUT SOURCE RESISTANCE in the
+	datasheet for details.
+
+Example:
+adc@0 {
+	compatible = "ti,adc12138";
+	reg = <0>;
+	interrupts = <28 IRQ_TYPE_EDGE_RISING>;
+	interrupt-parent = <&gpio1>;
+	clocks = <&cclk>;
+	vref-p-supply = <&ldo4_reg>;
+	spi-max-frequency = <5000000>;
+	ti,acquisition-time = <6>;
+};

drivers/iio/adc/Kconfig

@@ -438,6 +438,18 @@ config TI_ADC0832
 	  This driver can also be built as a module. If so, the module will be
 	  called ti-adc0832.
 
+config TI_ADC12138
+	tristate "Texas Instruments ADC12130/ADC12132/ADC12138"
+	depends on SPI
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  If you say yes here you get support for Texas Instruments ADC12130,
+	  ADC12132 and ADC12138 chips.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called ti-adc12138.
+
 config TI_ADC128S052
 	tristate "Texas Instruments ADC128S052/ADC122S021/ADC124S021"
 	depends on SPI

drivers/iio/adc/Makefile

@@ -42,6 +42,7 @@ obj-$(CONFIG_QCOM_SPMI_VADC) += qcom-spmi-vadc.o
 obj-$(CONFIG_ROCKCHIP_SARADC) += rockchip_saradc.o
 obj-$(CONFIG_TI_ADC081C) += ti-adc081c.o
 obj-$(CONFIG_TI_ADC0832) += ti-adc0832.o
+obj-$(CONFIG_TI_ADC12138) += ti-adc12138.o
 obj-$(CONFIG_TI_ADC128S052) += ti-adc128s052.o
 obj-$(CONFIG_TI_ADC161S626) += ti-adc161s626.o
 obj-$(CONFIG_TI_ADS1015) += ti-ads1015.o