iio: adc: Add Spreadtrum SC27XX PMICs ADC support

The Spreadtrum SC27XX PMICs ADC controller contains 32 channels,
which is used to sample voltages with 12 bits conversion.

[Baolin Wang did lots of improvements]
Signed-off-by: Freeman Liu <freeman.liu@spreadtrum.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/Kconfig

@@ -620,6 +620,16 @@ config ROCKCHIP_SARADC
 	  To compile this driver as a module, choose M here: the
 	  module will be called rockchip_saradc.
 
+config SC27XX_ADC
+	tristate "Spreadtrum SC27xx series PMICs ADC"
+	depends on MFD_SC27XX_PMIC || COMPILE_TEST
+	help
+	  Say yes here to build support for the integrated ADC inside the
+	  Spreadtrum SC27xx series PMICs.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called sc27xx_adc.
+
 config SPEAR_ADC
 	tristate "ST SPEAr ADC"
 	depends on PLAT_SPEAR || COMPILE_TEST

drivers/iio/adc/Makefile

@@ -59,6 +59,7 @@ obj-$(CONFIG_QCOM_SPMI_VADC) += qcom-spmi-vadc.o
 obj-$(CONFIG_QCOM_PM8XXX_XOADC) += qcom-pm8xxx-xoadc.o
 obj-$(CONFIG_RCAR_GYRO_ADC) += rcar-gyroadc.o
 obj-$(CONFIG_ROCKCHIP_SARADC) += rockchip_saradc.o
+obj-$(CONFIG_SC27XX_ADC) += sc27xx_adc.o
 obj-$(CONFIG_SPEAR_ADC) += spear_adc.o
 obj-$(CONFIG_STX104) += stx104.o
 obj-$(CONFIG_SUN4I_GPADC) += sun4i-gpadc-iio.o