power: ltc2941-battery-gauge: Disable continuous monitoring on shutdown

The driver sets the fuel gauge to continuous monitoring on startup, for
the models that support this. When the board shuts down, the chip remains
in that mode, causing a few mA drain on the battery every 2 or 10 seconds.

This patch registers a shutdown handler that turns off the monitoring to
prevent this battery drain.

Signed-off-by: Mike Looijmans <mike.looijmans@topic.nl>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.co.uk>

drivers/power/supply/ltc2941-battery-gauge.c

@@ -60,6 +60,7 @@ enum ltc294x_id {
 #define LTC294X_REG_CONTROL_PRESCALER_SET(x) \
 	((x << 3) & LTC294X_REG_CONTROL_PRESCALER_MASK)
 #define LTC294X_REG_CONTROL_ALCC_CONFIG_DISABLED	0
+#define LTC294X_REG_CONTROL_ADC_DISABLE(x)	((x) & ~(BIT(7) | BIT(6)))
 
 struct ltc294x_info {
 	struct i2c_client *client;	/* I2C Client pointer */
@@ -523,6 +524,29 @@ static int ltc294x_i2c_probe(struct i2c_client *client,
 	return 0;
 }
 
+static void ltc294x_i2c_shutdown(struct i2c_client *client)
+{
+	struct ltc294x_info *info = i2c_get_clientdata(client);
+	int ret;
+	u8 value;
+	u8 control;
+
+	/* The LTC2941 does not need any special handling */
+	if (info->id == LTC2941_ID)
+		return;
+
+	/* Read control register */
+	ret = ltc294x_read_regs(info->client, LTC294X_REG_CONTROL, &value, 1);
+	if (ret < 0)
+		return;
+
+	/* Disable continuous ADC conversion as this drains the battery */
+	control = LTC294X_REG_CONTROL_ADC_DISABLE(value);
+	if (control != value)
+		ltc294x_write_regs(info->client, LTC294X_REG_CONTROL,
+			&control, 1);
+}
+
 #ifdef CONFIG_PM_SLEEP
 
 static int ltc294x_suspend(struct device *dev)
@@ -589,6 +613,7 @@ static struct i2c_driver ltc294x_driver = {
 	},
 	.probe		= ltc294x_i2c_probe,
 	.remove		= ltc294x_i2c_remove,
+	.shutdown	= ltc294x_i2c_shutdown,
 	.id_table	= ltc294x_i2c_id,
 };
 module_i2c_driver(ltc294x_driver);