iio: adc: Add ad7124 support

The ad7124-4 and ad7124-8 are a family of 4 and 8 channel sigma-delta ADCs
with 24-bit precision and reference.

Three power modes are available which in turn affect the output data rate:
 * Full power: 9.38 SPS to 19,200 SPS
 * Mid power: 2.34 SPS to 4800 SPS
 * Low power: 1.17 SPS to 2400 SPS

The ad7124-4 can be configured to have four differential inputs, while
ad7124-8 can have 8. Moreover, ad7124 also supports per channel
configuration. Each configuration consists of gain, reference source,
output data rate and bipolar/unipolar configuration.

Datasheets:
Link: http://www.analog.com/media/en/technical-documentation/data-sheets/AD7124-4.pdf
Link: http://www.analog.com/media/en/technical-documentation/data-sheets/ad7124-8.pdfSigned-off-by: Stefan Popa <stefan.popa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

MAINTAINERS

@@ -839,6 +839,13 @@ S:	Supported
 F:	drivers/iio/dac/ad5758.c
 F:	Documentation/devicetree/bindings/iio/dac/ad5758.txt
 
+ANALOG DEVICES INC AD7124 DRIVER
+M:	Stefan Popa <stefan.popa@analog.com>
+L:	linux-iio@vger.kernel.org
+W:	http://ez.analog.com/community/linux-device-drivers
+S:	Supported
+F:	drivers/iio/adc/ad7124.c
+
 ANALOG DEVICES INC AD9389B DRIVER
 M:	Hans Verkuil <hans.verkuil@cisco.com>
 L:	linux-media@vger.kernel.org

drivers/iio/adc/Kconfig

@@ -10,6 +10,17 @@ config AD_SIGMA_DELTA
 	select IIO_BUFFER
 	select IIO_TRIGGERED_BUFFER
 
+config AD7124
+	tristate "Analog Devices AD7124 and similar sigma-delta ADCs driver"
+	depends on SPI_MASTER
+	select AD_SIGMA_DELTA
+	help
+	  Say yes here to build support for Analog Devices AD7124-4 and AD7124-8
+	  SPI analog to digital converters (ADC).
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called ad7124.
+
 config AD7266
 	tristate "Analog Devices AD7265/AD7266 ADC driver"
 	depends on SPI_MASTER

drivers/iio/adc/Makefile

@@ -5,6 +5,7 @@
 
 # When adding new entries keep the list in alphabetical order
 obj-$(CONFIG_AD_SIGMA_DELTA) += ad_sigma_delta.o
+obj-$(CONFIG_AD7124) += ad7124.o
 obj-$(CONFIG_AD7266) += ad7266.o
 obj-$(CONFIG_AD7291) += ad7291.o
 obj-$(CONFIG_AD7298) += ad7298.o