[RFC] hwmon: (dell_smm) Add cooling device support

diff --git a/Documentation/hwmon/dell-smm-hwmon.rst b/Documentation/hwmon/dell-smm-hwmon.rst
index d3323a96665d..da07e39935f1 100644
--- a/Documentation/hwmon/dell-smm-hwmon.rst
+++ b/Documentation/hwmon/dell-smm-hwmon.rst
@@ -86,6 +86,13 @@  probe the BIOS on your machine and discover the appropriate codes.

 Again, when you find new codes, we'd be happy to have your patches!

+``thermal`` interface
+---------------------------
+
+The driver also exports the fans as thermal cooling devices with
+``type`` set to ``dell-smm-fan``. This allows for easy fan control
+using one of the thermal governors.
+
 Module parameters
 -----------------

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index 84cb1ede7bc0..fb2c70875c0a 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -29,6 +29,7 @@ 
 #include <linux/seq_file.h>
 #include <linux/string.h>
 #include <linux/smp.h>
+#include <linux/thermal.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>

@@ -80,6 +81,11 @@  struct dell_smm_data {
 	int *fan_nominal_speed[DELL_SMM_NO_FANS];
 };

+struct dell_smm_cooling_data {
+	u8 fan_num;
+	struct dell_smm_data *data;
+};
+
 MODULE_AUTHOR("Massimo Dal Zotto (dz@debian.org)");
 MODULE_AUTHOR("Pali Rohár <pali@kernel.org>");
 MODULE_DESCRIPTION("Dell laptop SMM BIOS hwmon driver");
@@ -638,9 +644,50 @@  static void __init i8k_init_procfs(struct device *dev)

 #endif

-/*
- * Hwmon interface
- */
+static int dell_smm_get_max_state(struct thermal_cooling_device *dev, unsigned long *state)
+{
+	struct dell_smm_cooling_data *cdata = dev->devdata;
+
+	*state = cdata->data->i8k_fan_max;
+
+	return 0;
+}
+
+static int dell_smm_get_cur_state(struct thermal_cooling_device *dev, unsigned long *state)
+{
+	struct dell_smm_cooling_data *cdata = dev->devdata;
+	int ret;
+
+	ret = i8k_get_fan_speed(cdata->data, cdata->fan_num);
+	if (ret < 0)
+		return ret;
+
+	*state = ret;
+
+	return 0;
+}
+
+static int dell_smm_set_cur_state(struct thermal_cooling_device *dev, unsigned long state)
+{
+	struct dell_smm_cooling_data *cdata = dev->devdata;
+	struct dell_smm_data *data = cdata->data;
+	int ret;
+
+	if (state > data->i8k_fan_max)
+		return -EINVAL;
+
+	mutex_lock(&data->i8k_mutex);
+	ret = i8k_set_fan(data, cdata->fan_num, (int)state);
+	mutex_unlock(&data->i8k_mutex);
+
+	return ret;
+}
+
+static const struct thermal_cooling_device_ops dell_smm_cooling_ops = {
+	.get_max_state = dell_smm_get_max_state,
+	.get_cur_state = dell_smm_get_cur_state,
+	.set_cur_state = dell_smm_set_cur_state,
+};

 static umode_t dell_smm_is_visible(const void *drvdata, enum hwmon_sensor_types type, u32 attr,
 				   int channel)
@@ -944,6 +991,8 @@  static const struct hwmon_chip_info dell_smm_chip_info = {
 static int __init dell_smm_init_hwmon(struct device *dev)
 {
 	struct dell_smm_data *data = dev_get_drvdata(dev);
+	struct thermal_cooling_device *cdev;
+	struct dell_smm_cooling_data *cdata;
 	struct device *dell_smm_hwmon_dev;
 	int state, err;
 	u8 i;
@@ -967,6 +1016,19 @@  static int __init dell_smm_init_hwmon(struct device *dev)
 			continue;

 		data->fan[i] = true;
+
+		/* the cooling device it not critical, ignore failures */
+		cdata = devm_kmalloc(dev, sizeof(*cdata), GFP_KERNEL);
+		if (cdata) {
+			cdata->fan_num = i;
+			cdata->data = data;
+			cdev = devm_thermal_of_cooling_device_register(dev, NULL, "dell-smm-fan",
+								       cdata,
+								       &dell_smm_cooling_ops);
+			if (IS_ERR(cdev))
+				devm_kfree(dev, cdata);
+		}
+
 		data->fan_nominal_speed[i] = devm_kmalloc_array(dev, data->i8k_fan_max + 1,
 								sizeof(*data->fan_nominal_speed[i]),
 								GFP_KERNEL);