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 <[e-mail]>
Signed-off-by: Anton Vorontsov <[e-mail]>

Documentation/power/power_supply_class.txt

···
 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

···
 	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,
···
 		break;
 	case POWER_SUPPLY_PROP_VOLTAGE_AVG:
 		ret = max17042_read_reg(chip->client, MAX17042_AvgVCELL);
+		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;
 

drivers/power/power_supply_sysfs.c

···
 	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

···
 	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,
···
 	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: