HID: logitech-hidpp: BatteryVoltage: only read chargeStatus if extPower is active

In the HID++ 2.0 function getBatteryInfo() from the BatteryVoltage
(0x1001) feature, chargeStatus is only valid if extPower is active.

Previously we were ignoring extPower, which resulted in wrong values.

Example:
    With an unplugged mouse

    $ cat /sys/class/power_supply/hidpp_battery_0/status
    Charging

This patch fixes that, it also renames charge_sts to flags as
charge_sts can be confused with chargeStatus from the spec.

Spec:
+--------+-------------------------------------------------------------------------+
|  byte  |                                    2                                    |
+--------+--------------+------------+------------+----------+----------+----------+
|   bit  |     0..2     |      3     |      4     |     5    |     6    |     7    |
+--------+--------------+------------+------------+----------+----------+----------+
| buffer | chargeStatus | fastCharge | slowCharge | critical | (unused) | extPower |
+--------+--------------+------------+------------+----------+----------+----------+
Table 1 - battery voltage (0x1001), getBatteryInfo() (ASE 0), 3rd byte

+-------+--------------------------------------+
| value |                meaning               |
+-------+--------------------------------------+
|   0   | Charging                             |
+-------+--------------------------------------+
|   1   | End of charge (100% charged)         |
+-------+--------------------------------------+
|   2   | Charge stopped (any "normal" reason) |
+-------+--------------------------------------+
|   7   | Hardware error                       |
+-------+--------------------------------------+
Table 2 - chargeStatus value
Signed-off-by: Filipe Laíns <lains@archlinux.org>
Tested-by: Pedro Vanzella <pedro@pedrovanzella.com>
Reviewed-by: Pedro Vanzella <pedro@pedrovanzella.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

drivers/hid/hid-logitech-hidpp.c

@@ -1256,36 +1256,35 @@ static int hidpp20_battery_map_status_voltage(u8 data[3], int *voltage,
 {
 	int status;
 
-	long charge_sts = (long)data[2];
+	long flags = (long) data[2];
 
-	*level = POWER_SUPPLY_CAPACITY_LEVEL_UNKNOWN;
-	switch (data[2] & 0xe0) {
-	case 0x00:
+	if (flags & 0x80)
+		switch (flags & 0x07) {
+		case 0:
 			status = POWER_SUPPLY_STATUS_CHARGING;
 			break;
-	case 0x20:
+		case 1:
 			status = POWER_SUPPLY_STATUS_FULL;
 			*level = POWER_SUPPLY_CAPACITY_LEVEL_FULL;
 			break;
-	case 0x40:
-		status = POWER_SUPPLY_STATUS_DISCHARGING;
-		break;
-	case 0xe0:
+		case 2:
 			status = POWER_SUPPLY_STATUS_NOT_CHARGING;
 			break;
 		default:
 			status = POWER_SUPPLY_STATUS_UNKNOWN;
+			break;
 		}
+	else
+		status = POWER_SUPPLY_STATUS_DISCHARGING;
 
 	*charge_type = POWER_SUPPLY_CHARGE_TYPE_STANDARD;
-	if (test_bit(3, &charge_sts)) {
+	if (test_bit(3, &flags)) {
 		*charge_type = POWER_SUPPLY_CHARGE_TYPE_FAST;
 	}
-	if (test_bit(4, &charge_sts)) {
+	if (test_bit(4, &flags)) {
 		*charge_type = POWER_SUPPLY_CHARGE_TYPE_TRICKLE;
 	}
-
-	if (test_bit(5, &charge_sts)) {
+	if (test_bit(5, &flags)) {
 		*level = POWER_SUPPLY_CAPACITY_LEVEL_CRITICAL;
 	}