iio: add support of the max1027

This driver add partial support of the
maxim 1027/1029/1031. Differential mode is not
supported.

It was tested on armadeus apf27 board.
Signed-off-by: Philippe Reynes <tremyfr@yahoo.fr>
Reviewed-by: Hartmut Knaack <knaack.h@gmx.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Documentation/devicetree/bindings/iio/adc/max1027-adc.txt

+* Maxim 1027/1029/1031 Analog to Digital Converter (ADC)
+
+Required properties:
+  - compatible: Should be "maxim,max1027" or "maxim,max1029" or "maxim,max1031"
+  - reg: SPI chip select number for the device
+  - interrupt-parent: phandle to the parent interrupt controller
+  see: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
+  - interrupts: IRQ line for the ADC
+  see: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
+
+Recommended properties:
+- spi-max-frequency: Definition as per
+                     Documentation/devicetree/bindings/spi/spi-bus.txt
+
+Example:
+adc@0 {
+	compatible = "maxim,max1027";
+	reg = <0>;
+	interrupt-parent = <&gpio5>;
+	interrupts = <15 IRQ_TYPE_EDGE_RISING>;
+	spi-max-frequency = <1000000>;
+};

drivers/iio/adc/Kconfig

@@ -131,6 +131,15 @@ config LP8788_ADC
 	help
 	  Say yes here to build support for TI LP8788 ADC.
 
+config MAX1027
+	tristate "Maxim max1027 ADC driver"
+	depends on SPI
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say yes here to build support for Maxim SPI ADC models
+	  max1027, max1029 and max1031.
+
 config MAX1363
 	tristate "Maxim max1363 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -15,6 +15,7 @@ obj-$(CONFIG_AD799X) += ad799x.o
 obj-$(CONFIG_AT91_ADC) += at91_adc.o
 obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o
 obj-$(CONFIG_LP8788_ADC) += lp8788_adc.o
+obj-$(CONFIG_MAX1027) += max1027.o
 obj-$(CONFIG_MAX1363) += max1363.o
 obj-$(CONFIG_MCP320X) += mcp320x.o
 obj-$(CONFIG_MCP3422) += mcp3422.o