power_supply: Add voltage_ocv property and use it for max17042 driver

This adds a new sysfs file called 'voltage_ocv' which gives the
Open Circuit Voltage of the battery.

This property can be used for platform shutdown policies and
can be useful for initial capacity estimations.

Note: This patch is generated against linux-next branch.
Signed-off-by: Ramakrishna Pallala <ramakrishna.pallala@intel.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>

Documentation/power/power_supply_class.txt

@@ -84,6 +84,8 @@ are already charged or discharging, 'n/a' can be displayed (or
 HEALTH - represents health of the battery, values corresponds to
 POWER_SUPPLY_HEALTH_*, defined in battery.h.
 
+VOLTAGE_OCV - open circuit voltage of the battery.
+
 VOLTAGE_MAX_DESIGN, VOLTAGE_MIN_DESIGN - design values for maximal and
 minimal power supply voltages. Maximal/minimal means values of voltages
 when battery considered "full"/"empty" at normal conditions. Yes, there is

drivers/power/max17042_battery.c

@@ -106,6 +106,7 @@ static enum power_supply_property max17042_battery_props[] = {
 	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
 	POWER_SUPPLY_PROP_VOLTAGE_NOW,
 	POWER_SUPPLY_PROP_VOLTAGE_AVG,
+	POWER_SUPPLY_PROP_VOLTAGE_OCV,
 	POWER_SUPPLY_PROP_CAPACITY,
 	POWER_SUPPLY_PROP_CHARGE_FULL,
 	POWER_SUPPLY_PROP_TEMP,
@@ -170,6 +171,13 @@ static int max17042_get_property(struct power_supply *psy,
 		if (ret < 0)
 			return ret;
 
+		val->intval = ret * 625 / 8;
+		break;
+	case POWER_SUPPLY_PROP_VOLTAGE_OCV:
+		ret = max17042_read_reg(chip->client, MAX17042_OCVInternal);
+		if (ret < 0)
+			return ret;
+
 		val->intval = ret * 625 / 8;
 		break;
 	case POWER_SUPPLY_PROP_CAPACITY:

drivers/power/power_supply_sysfs.c

@@ -146,6 +146,7 @@ static struct device_attribute power_supply_attrs[] = {
 	POWER_SUPPLY_ATTR(voltage_min_design),
 	POWER_SUPPLY_ATTR(voltage_now),
 	POWER_SUPPLY_ATTR(voltage_avg),
+	POWER_SUPPLY_ATTR(voltage_ocv),
 	POWER_SUPPLY_ATTR(current_max),
 	POWER_SUPPLY_ATTR(current_now),
 	POWER_SUPPLY_ATTR(current_avg),

include/linux/power_supply.h

@@ -96,6 +96,7 @@ enum power_supply_property {
 	POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN,
 	POWER_SUPPLY_PROP_VOLTAGE_NOW,
 	POWER_SUPPLY_PROP_VOLTAGE_AVG,
+	POWER_SUPPLY_PROP_VOLTAGE_OCV,
 	POWER_SUPPLY_PROP_CURRENT_MAX,
 	POWER_SUPPLY_PROP_CURRENT_NOW,
 	POWER_SUPPLY_PROP_CURRENT_AVG,
@@ -261,6 +262,7 @@ static inline bool power_supply_is_watt_property(enum power_supply_property psp)
 	case POWER_SUPPLY_PROP_VOLTAGE_MIN_DESIGN:
 	case POWER_SUPPLY_PROP_VOLTAGE_NOW:
 	case POWER_SUPPLY_PROP_VOLTAGE_AVG:
+	case POWER_SUPPLY_PROP_VOLTAGE_OCV:
 	case POWER_SUPPLY_PROP_POWER_NOW:
 		return 1;
 	default: