power: max17040: get thermal data from adc if available

Since fuel gauge does not support thermal monitoring,
some vendors may couple this fuel gauge with thermal/adc
sensor to monitor battery cell exact temperature.

Add this feature by adding optional iio thermal channel.
Signed-off-by: Svyatoslav Ryhel <clamor95@gmail.com>
Reviewed-by: Iskren Chernev <me@iskren.info>
Link: https://lore.kernel.org/r/20230731073613.10394-4-clamor95@gmail.comSigned-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/Kconfig

@@ -374,7 +374,7 @@ config AXP288_FUEL_GAUGE
 
 config BATTERY_MAX17040
 	tristate "Maxim MAX17040/17041/17043 family Fuel Gauge"
-	depends on I2C
+	depends on I2C && IIO
 	select REGMAP_I2C
 	help
 	  Driver supports Maxim fuel-gauge systems for lithium-ion (Li+)

drivers/power/supply/max17040_battery.c

@@ -18,6 +18,7 @@
 #include <linux/of.h>
 #include <linux/regmap.h>
 #include <linux/slab.h>
+#include <linux/iio/consumer.h>
 
 #define MAX17040_VCELL	0x02
 #define MAX17040_SOC	0x04
@@ -142,6 +143,7 @@ struct max17040_chip {
 	struct delayed_work		work;
 	struct power_supply		*battery;
 	struct chip_data		data;
+	struct iio_channel		*channel_temp;
 
 	/* battery capacity */
 	int soc;
@@ -404,6 +406,13 @@ static int max17040_get_property(struct power_supply *psy,
 	case POWER_SUPPLY_PROP_STATUS:
 		power_supply_get_property_from_supplier(psy, psp, val);
 		break;
+	case POWER_SUPPLY_PROP_TEMP:
+		if (!chip->channel_temp)
+			return -ENODATA;
+
+		iio_read_channel_processed_scale(chip->channel_temp,
+						 &val->intval, 10);
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -424,6 +433,7 @@ static enum power_supply_property max17040_battery_props[] = {
 	POWER_SUPPLY_PROP_CAPACITY,
 	POWER_SUPPLY_PROP_CAPACITY_ALERT_MIN,
 	POWER_SUPPLY_PROP_STATUS,
+	POWER_SUPPLY_PROP_TEMP,
 };
 
 static const struct power_supply_desc max17040_battery_desc = {
@@ -469,6 +479,17 @@ static int max17040_probe(struct i2c_client *client)
 	i2c_set_clientdata(client, chip);
 	psy_cfg.drv_data = chip;
 
+	/* Switch to devm_iio_channel_get_optional when available  */
+	chip->channel_temp = devm_iio_channel_get(&client->dev, "temp");
+	if (IS_ERR(chip->channel_temp)) {
+		ret = PTR_ERR(chip->channel_temp);
+		if (ret != -ENODEV)
+			return dev_err_probe(&client->dev, PTR_ERR(chip->channel_temp),
+					     "failed to get temp\n");
+		else
+			chip->channel_temp = NULL;
+	}
+
 	chip->battery = devm_power_supply_register(&client->dev,
 				&max17040_battery_desc, &psy_cfg);
 	if (IS_ERR(chip->battery)) {