hwmon: Support thermal zones registration for SCP temperature sensors

Add support to create thermal zones based on the temperature sensors
provided by the SCP. The thermal zones can be defined using the
thermal DT bindings and should refer to the SCP sensor id to select
the sensor.
Signed-off-by: Punit Agrawal <punit.agrawal@arm.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Cc: Eduardo Valentin <edubezval@gmail.com>

drivers/hwmon/scpi-hwmon.c

@@ -20,6 +20,7 @@
 #include <linux/scpi_protocol.h>
 #include <linux/slab.h>
 #include <linux/sysfs.h>
+#include <linux/thermal.h>
 
 struct sensor_data {
 	struct scpi_sensor_info info;
@@ -29,14 +30,39 @@ struct sensor_data {
 	char label[20];
 };
 
+struct scpi_thermal_zone {
+	struct list_head list;
+	int sensor_id;
+	struct scpi_sensors *scpi_sensors;
+	struct thermal_zone_device *tzd;
+};
+
 struct scpi_sensors {
 	struct scpi_ops *scpi_ops;
 	struct sensor_data *data;
+	struct list_head thermal_zones;
 	struct attribute **attrs;
 	struct attribute_group group;
 	const struct attribute_group *groups[2];
 };
 
+static int scpi_read_temp(void *dev, int *temp)
+{
+	struct scpi_thermal_zone *zone = dev;
+	struct scpi_sensors *scpi_sensors = zone->scpi_sensors;
+	struct scpi_ops *scpi_ops = scpi_sensors->scpi_ops;
+	struct sensor_data *sensor = &scpi_sensors->data[zone->sensor_id];
+	u32 value;
+	int ret;
+
+	ret = scpi_ops->sensor_get_value(sensor->info.sensor_id, &value);
+	if (ret)
+		return ret;
+
+	*temp = value;
+	return 0;
+}
+
 /* hwmon callback functions */
 static ssize_t
 scpi_show_sensor(struct device *dev, struct device_attribute *attr, char *buf)
@@ -66,6 +92,24 @@ scpi_show_label(struct device *dev, struct device_attribute *attr, char *buf)
 	return sprintf(buf, "%s\n", sensor->info.name);
 }
 
+static void
+unregister_thermal_zones(struct platform_device *pdev,
+			 struct scpi_sensors *scpi_sensors)
+{
+	struct list_head *pos;
+
+	list_for_each(pos, &scpi_sensors->thermal_zones) {
+		struct scpi_thermal_zone *zone;
+
+		zone = list_entry(pos, struct scpi_thermal_zone, list);
+		thermal_zone_of_sensor_unregister(&pdev->dev, zone->tzd);
+	}
+}
+
+static struct thermal_zone_of_device_ops scpi_sensor_ops = {
+	.get_temp = scpi_read_temp,
+};
+
 static int scpi_hwmon_probe(struct platform_device *pdev)
 {
 	u16 nr_sensors, i;
@@ -160,10 +204,67 @@ static int scpi_hwmon_probe(struct platform_device *pdev)
 	scpi_sensors->group.attrs = scpi_sensors->attrs;
 	scpi_sensors->groups[0] = &scpi_sensors->group;
 
+	platform_set_drvdata(pdev, scpi_sensors);
+
 	hwdev = devm_hwmon_device_register_with_groups(dev,
 			"scpi_sensors", scpi_sensors, scpi_sensors->groups);
 
-	return PTR_ERR_OR_ZERO(hwdev);
+	if (IS_ERR(hwdev))
+		return PTR_ERR(hwdev);
+
+	/*
+	 * Register the temperature sensors with the thermal framework
+	 * to allow their usage in setting up the thermal zones from
+	 * device tree.
+	 *
+	 * NOTE: Not all temperature sensors maybe used for thermal
+	 * control
+	 */
+	INIT_LIST_HEAD(&scpi_sensors->thermal_zones);
+	for (i = 0; i < nr_sensors; i++) {
+		struct sensor_data *sensor = &scpi_sensors->data[i];
+		struct scpi_thermal_zone *zone;
+
+		if (sensor->info.class != TEMPERATURE)
+			continue;
+
+		zone = devm_kzalloc(dev, sizeof(*zone), GFP_KERNEL);
+		if (!zone) {
+			ret = -ENOMEM;
+			goto unregister_tzd;
+		}
+
+		zone->sensor_id = i;
+		zone->scpi_sensors = scpi_sensors;
+		zone->tzd = thermal_zone_of_sensor_register(dev, i, zone,
+							    &scpi_sensor_ops);
+		/*
+		 * The call to thermal_zone_of_sensor_register returns
+		 * an error for sensors that are not associated with
+		 * any thermal zones or if the thermal subsystem is
+		 * not configured.
+		 */
+		if (IS_ERR(zone->tzd)) {
+			devm_kfree(dev, zone);
+			continue;
+		}
+		list_add(&zone->list, &scpi_sensors->thermal_zones);
+	}
+
+	return 0;
+
+unregister_tzd:
+	unregister_thermal_zones(pdev, scpi_sensors);
+	return ret;
+}
+
+static int scpi_hwmon_remove(struct platform_device *pdev)
+{
+	struct scpi_sensors *scpi_sensors = platform_get_drvdata(pdev);
+
+	unregister_thermal_zones(pdev, scpi_sensors);
+
+	return 0;
 }
 
 static const struct of_device_id scpi_of_match[] = {
@@ -178,6 +279,7 @@ static struct platform_driver scpi_hwmon_platdrv = {
 		.of_match_table = scpi_of_match,
 	},
 	.probe		= scpi_hwmon_probe,
+	.remove		= scpi_hwmon_remove,
 };
 module_platform_driver(scpi_hwmon_platdrv);