iio: adc: add support for X-Powers AXP20X and AXP22X PMICs ADCs

The X-Powers AXP20X and AXP22X PMICs have multiple ADCs. They expose the
battery voltage, battery charge and discharge currents, AC-in and VBUS
voltages and currents, 2 GPIOs muxable in ADC mode and PMIC temperature.

This adds support for most of AXP20X and AXP22X ADCs.
Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Reviewed-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/iio/adc/Kconfig

@@ -154,6 +154,16 @@ config AT91_SAMA5D2_ADC
 	  To compile this driver as a module, choose M here: the module will be
 	  called at91-sama5d2_adc.
 
+config AXP20X_ADC
+	tristate "X-Powers AXP20X and AXP22X ADC driver"
+	depends on MFD_AXP20X
+	help
+	  Say yes here to have support for X-Powers power management IC (PMIC)
+	  AXP20X and AXP22X ADC devices.
+
+	  To compile this driver as a module, choose M here: the module will be
+	  called axp20x_adc.
+
 config AXP288_ADC
 	tristate "X-Powers AXP288 ADC driver"
 	depends on MFD_AXP20X

drivers/iio/adc/Makefile

@@ -16,6 +16,7 @@ obj-$(CONFIG_AD7887) += ad7887.o
 obj-$(CONFIG_AD799X) += ad799x.o
 obj-$(CONFIG_AT91_ADC) += at91_adc.o
 obj-$(CONFIG_AT91_SAMA5D2_ADC) += at91-sama5d2_adc.o
+obj-$(CONFIG_AXP20X_ADC) += axp20x_adc.o
 obj-$(CONFIG_AXP288_ADC) += axp288_adc.o
 obj-$(CONFIG_BCM_IPROC_ADC) += bcm_iproc_adc.o
 obj-$(CONFIG_BERLIN2_ADC) += berlin2-adc.o