hwmon: (ntc_thermistor) Add ntc thermistor to thermal subsystem as a sensor.

To get more comprehensive and integrated thermal management, it adds ntc
thermistor to thermal framework as a thermal sensor. It's governed thermal
susbsystem only if it is described in DT node. Otherwise, it just notifies
temperature to userspace via sysfs as it used to be.

Signed-off-by: Jonghwa Lee <jonghwa3.lee@samsung.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/devicetree/bindings/hwmon/ntc_thermistor.txt

@@ -25,6 +25,9 @@ Requires node properties:
 - "io-channels"	Channel node of ADC to be used for
 		conversion.
 
+Optional node properties:
+- "#thermal-sensor-cells" Used to expose itself to thermal fw.
+
 Read more about iio bindings at
 	Documentation/devicetree/bindings/iio/iio-bindings.txt
 

drivers/hwmon/Kconfig

@@ -1077,6 +1077,7 @@ config SENSORS_PC87427
 config SENSORS_NTC_THERMISTOR
 	tristate "NTC thermistor support from Murata"
 	depends on !OF || IIO=n || IIO
+	depends on THERMAL || !THERMAL_OF
 	help
 	  This driver supports NTC thermistors sensor reading and its
 	  interpretation. The driver can also monitor the temperature and

drivers/hwmon/ntc_thermistor.c

@@ -38,6 +38,7 @@
 
 #include <linux/hwmon.h>
 #include <linux/hwmon-sysfs.h>
+#include <linux/thermal.h>
 
 struct ntc_compensation {
 	int		temp_c;
@@ -182,6 +183,7 @@ struct ntc_data {
 	struct device *dev;
 	int n_comp;
 	char name[PLATFORM_NAME_SIZE];
+	struct thermal_zone_device *tz;
 };
 
 #if defined(CONFIG_OF) && IS_ENABLED(CONFIG_IIO)
@@ -428,6 +430,20 @@ static int ntc_thermistor_get_ohm(struct ntc_data *data)
 	return -EINVAL;
 }
 
+static int ntc_read_temp(void *dev, long *temp)
+{
+	struct ntc_data *data = dev_get_drvdata(dev);
+	int ohm;
+
+	ohm = ntc_thermistor_get_ohm(data);
+	if (ohm < 0)
+		return ohm;
+
+	*temp = get_temp_mc(data, ohm);
+
+	return 0;
+}
+
 static ssize_t ntc_show_name(struct device *dev,
 		struct device_attribute *attr, char *buf)
 {
@@ -562,6 +578,13 @@ static int ntc_thermistor_probe(struct platform_device *pdev)
 	dev_info(&pdev->dev, "Thermistor type: %s successfully probed.\n",
 								pdev_id->name);
 
+	data->tz = thermal_zone_of_sensor_register(data->dev, 0, data->dev,
+						ntc_read_temp, NULL);
+	if (IS_ERR(data->tz)) {
+		dev_dbg(&pdev->dev, "Failed to register to thermal fw.\n");
+		data->tz = NULL;
+	}
+
 	return 0;
 err_after_sysfs:
 	sysfs_remove_group(&data->dev->kobj, &ntc_attr_group);
@@ -578,6 +601,8 @@ static int ntc_thermistor_remove(struct platform_device *pdev)
 	sysfs_remove_group(&data->dev->kobj, &ntc_attr_group);
 	ntc_iio_channel_release(pdata);
 
+	thermal_zone_of_sensor_unregister(data->dev, data->tz);
+
 	return 0;
 }