iio: adc: cpcap: Add minimal support for CPCAP PMIC ADC

On Motorola phones like droid 4 there is a custom CPCAP PMIC. This PMIC
has ADCs that are used for battery charging and USB PHY VBUS and ID pin
detection.

Unfortunately the only documentation for this ADC seems to be the
Motorola mapphone Linux kernel tree. I have tested that reading raw and
scaled values works, but I have not used the timed sampling that the ADC
seems to support.

Let's add a minimal support for it so we can eventually provide IIO
channels for the related battery charging and USB PHY drivers.

Cc: devicetree@vger.kernel.org
Cc: Marcel Partap <mpartap@gmx.net>
Cc: Michael Scott <michael.scott@linaro.org>
Cc: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

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

+Motorola CPCAP PMIC ADC binding
+
+Required properties:
+- compatible: Should be "motorola,cpcap-adc" or "motorola,mapphone-cpcap-adc"
+- interrupt-parent: The interrupt controller
+- interrupts: The interrupt number for the ADC device
+- interrupt-names: Should be "adcdone"
+- #io-channel-cells: Number of cells in an IIO specifier
+
+Example:
+
+cpcap_adc: adc {
+	compatible = "motorola,mapphone-cpcap-adc";
+	interrupt-parent = <&cpcap>;
+	interrupts = <8 IRQ_TYPE_NONE>;
+	interrupt-names = "adcdone";
+	#io-channel-cells = <1>;
+};

drivers/iio/adc/Kconfig

@@ -195,6 +195,17 @@ config CC10001_ADC
 	  This driver can also be built as a module. If so, the module will be
 	  called cc10001_adc.
 
+config CPCAP_ADC
+	tristate "Motorola CPCAP PMIC ADC driver"
+	depends on MFD_CPCAP
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say yes here to build support for Motorola CPCAP PMIC ADC.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called cpcap-adc.
+
 config DA9150_GPADC
 	tristate "Dialog DA9150 GPADC driver support"
 	depends on MFD_DA9150

drivers/iio/adc/Makefile

@@ -20,6 +20,7 @@ obj-$(CONFIG_AXP288_ADC) += axp288_adc.o
 obj-$(CONFIG_BCM_IPROC_ADC) += bcm_iproc_adc.o
 obj-$(CONFIG_BERLIN2_ADC) += berlin2-adc.o
 obj-$(CONFIG_CC10001_ADC) += cc10001_adc.o
+obj-$(CONFIG_CPCAP_ADC) += cpcap-adc.o
 obj-$(CONFIG_DA9150_GPADC) += da9150-gpadc.o
 obj-$(CONFIG_ENVELOPE_DETECTOR) += envelope-detector.o
 obj-$(CONFIG_EXYNOS_ADC) += exynos_adc.o