PM / devfreq: Register devfreq as a cooling device on demand

Currently the default behavior is to manually having the devfreq
backend to register themselves as a devfreq cooling device.

Instead of adding the code in the drivers for the thermal cooling
device registering, let's provide a flag in the devfreq's profile to
tell the common devfreq code to register the newly created devfreq as
a cooling device.

Suggested-by: Chanwoo Choi <[e-mail]>
Signed-off-by: Daniel Lezcano <[e-mail]>
Reviewed-by: Steven Price <[e-mail]>
Reviewed-by: Lukasz Luba <[e-mail]>
Signed-off-by: Chanwoo Choi <[e-mail]>

drivers/devfreq/devfreq.c

···
 #include <linux/kmod.h>
 #include <linux/sched.h>
 #include <linux/debugfs.h>
+#include <linux/devfreq_cooling.h>
 #include <linux/errno.h>
 #include <linux/err.h>
 #include <linux/init.h>
···
 
 	mutex_unlock(&devfreq_list_lock);
 
+	if (devfreq->profile->is_cooling_device) {
+		devfreq->cdev = devfreq_cooling_em_register(devfreq, NULL);
+		if (IS_ERR(devfreq->cdev))
+			devfreq->cdev = NULL;
+	}
+
 	return devfreq;
 
 err_init:
···
 {
 	if (!devfreq)
 		return -EINVAL;
+
+	devfreq_cooling_unregister(devfreq->cdev);
 
 	if (devfreq->governor) {
 		devfreq->governor->event_handler(devfreq,

include/linux/devfreq.h

···
 
 struct devfreq;
 struct devfreq_governor;
+struct thermal_cooling_device;
 
 /**
  * struct devfreq_dev_status - Data given from devfreq user device to
···
  * @freq_table:		Optional list of frequencies to support statistics
  *			and freq_table must be generated in ascending order.
  * @max_state:		The size of freq_table.
+ *
+ * @is_cooling_device: A self-explanatory boolean giving the device a
+ *                     cooling effect property.
  */
 struct devfreq_dev_profile {
 	unsigned long initial_freq;
 	unsigned int polling_ms;
 	enum devfreq_timer timer;
+	bool is_cooling_device;
 
 	int (*target)(struct device *dev, unsigned long *freq, u32 flags);
 	int (*get_dev_status)(struct device *dev,
···
  * @suspend_count:	 suspend requests counter for a device.
  * @stats:	Statistics of devfreq device behavior
  * @transition_notifier_list: list head of DEVFREQ_TRANSITION_NOTIFIER notifier
+ * @cdev:	Cooling device pointer if the devfreq has cooling property
  * @nb_min:		Notifier block for DEV_PM_QOS_MIN_FREQUENCY
  * @nb_max:		Notifier block for DEV_PM_QOS_MAX_FREQUENCY
  *
···
 	struct devfreq_stats stats;
 
 	struct srcu_notifier_head transition_notifier_list;
+
+	/* Pointer to the cooling device if used for thermal mitigation */
+	struct thermal_cooling_device *cdev;
 
 	struct notifier_block nb_min;
 	struct notifier_block nb_max;