power: supply: sbs-battery: Prevent CAPACITY_MODE races

A subset of smart battery commands return charge or energy depending on
the CAPACITY_MODE bit setting of BatteryMode(). In order to
unambiguously read a charge or energy value, it is necessary to ensure
that CAPACITY_MODE is set as desired, and not changed for the duration
of the attribute read.
Signed-off-by: Shawn Nematbakhsh <shawnn@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

drivers/power/supply/sbs-battery.c

@@ -171,6 +171,7 @@ struct sbs_info {
 	u32				i2c_retry_count;
 	u32				poll_retry_count;
 	struct delayed_work		work;
+	struct mutex			mode_lock;
 };
 
 static char model_name[I2C_SMBUS_BLOCK_MAX + 1];
@@ -622,7 +623,13 @@ static int sbs_get_property(struct power_supply *psy,
 		if (ret < 0)
 			break;
 
+		/* sbs_get_battery_capacity() will change the battery mode
+		 * temporarily to read the requested attribute. Ensure we stay
+		 * in the desired mode for the duration of the attribute read.
+		 */
+		mutex_lock(&chip->mode_lock);
 		ret = sbs_get_battery_capacity(client, ret, psp, val);
+		mutex_unlock(&chip->mode_lock);
 		break;
 
 	case POWER_SUPPLY_PROP_SERIAL_NUMBER:
@@ -807,6 +814,7 @@ static int sbs_probe(struct i2c_client *client,
 	psy_cfg.of_node = client->dev.of_node;
 	psy_cfg.drv_data = chip;
 	chip->last_state = POWER_SUPPLY_STATUS_UNKNOWN;
+	mutex_init(&chip->mode_lock);
 
 	/* use pdata if available, fall back to DT properties,
 	 * or hardcoded defaults if not