ACPI: battery: negate current when discharging

The ACPI specification requires that battery rate is always positive,
but the kernel ABI for POWER_SUPPLY_PROP_CURRENT_NOW
(Documentation/ABI/testing/sysfs-class-power) specifies that it should
be negative when a battery is discharging. When reporting CURRENT_NOW,
massage the value to match the documented ABI.

This only changes the sign of `current_now` and not `power_now` because
documentation doesn't describe any particular meaning for `power_now` so
leaving `power_now` unchanged is less likely to confuse userspace
unnecessarily, whereas becoming consistent with the documented ABI is
worth potentially confusing clients that read `current_now`.

Signed-off-by: Peter Marheine <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Rafael J. Wysocki <[email protected]>

Author: tari

drivers/acpi/battery.c

@@ -243,10 +243,23 @@ static int acpi_battery_get_property(struct power_supply *psy,
 		break;
 	case POWER_SUPPLY_PROP_CURRENT_NOW:
 	case POWER_SUPPLY_PROP_POWER_NOW:
-		if (battery->rate_now == ACPI_BATTERY_VALUE_UNKNOWN)
+		if (battery->rate_now == ACPI_BATTERY_VALUE_UNKNOWN) {
 			ret = -ENODEV;
-		else
-			val->intval = battery->rate_now * 1000;
+			break;
+		}
+
+		val->intval = battery->rate_now * 1000;
+		/*
+		 * When discharging, the current should be reported as a
+		 * negative number as per the power supply class interface
+		 * definition.
+		 */
+		if (psp == POWER_SUPPLY_PROP_CURRENT_NOW &&
+		    (battery->state & ACPI_BATTERY_STATE_DISCHARGING) &&
+		    acpi_battery_handle_discharging(battery)
+				== POWER_SUPPLY_STATUS_DISCHARGING)
+			val->intval = -val->intval;
+
 		break;
 	case POWER_SUPPLY_PROP_CHARGE_FULL_DESIGN:
 	case POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN: