power: supply: add battery driver for AXP20X and AXP22X PMICs

The X-Powers AXP20X and AXP22X PMICs can have a battery as power supply.

This patch adds the battery power supply driver to get various data from
the PMIC, such as the battery status (charging, discharging, full,
dead), current max limit, current current, battery capacity (in
percentage), voltage max and min limits, current voltage and battery
capacity (in Ah).

This battery driver uses the AXP20X/AXP22X ADC driver as PMIC data
provider.
Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

drivers/power/supply/Kconfig

@@ -238,6 +238,18 @@ config CHARGER_AXP20X
 	  This driver can also be built as a module. If so, the module will be
 	  called axp20x_ac_power.
 
+config BATTERY_AXP20X
+	tristate "X-Powers AXP20X battery driver"
+	depends on MFD_AXP20X
+	depends on AXP20X_ADC
+	depends on IIO
+	help
+	  Say Y here to enable support for X-Powers AXP20X PMICs' battery power
+	  supply.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called axp20x_battery.
+
 config AXP288_CHARGER
 	tristate "X-Powers AXP288 Charger"
 	depends on MFD_AXP20X && EXTCON_AXP288

drivers/power/supply/Makefile

@@ -18,6 +18,7 @@ obj-$(CONFIG_TEST_POWER)	+= test_power.o
 
 obj-$(CONFIG_BATTERY_88PM860X)	+= 88pm860x_battery.o
 obj-$(CONFIG_BATTERY_ACT8945A)	+= act8945a_charger.o
+obj-$(CONFIG_BATTERY_AXP20X)	+= axp20x_battery.o
 obj-$(CONFIG_CHARGER_AXP20X)	+= axp20x_ac_power.o
 obj-$(CONFIG_BATTERY_DS2760)	+= ds2760_battery.o
 obj-$(CONFIG_BATTERY_DS2780)	+= ds2780_battery.o