thermal: core: Allocate thermal_class statically

Define thermal_class as a static structure to simplify thermal_init()
and to simplify thermal class availability checks that will need to
be carried out during the suspend and resume of thermal zones after
subsequent changes.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://patch.msgid.link/10831981.nUPlyArG6x@rafael.j.wysocki

Author: rafaeljw

drivers/thermal/thermal_core.c

@@ -972,7 +972,11 @@ static void thermal_release(struct device *dev)
 	}
 }
 
-static struct class *thermal_class;
+static const struct class thermal_class = {
+	.name = "thermal",
+	.dev_release = thermal_release,
+};
+static bool thermal_class_unavailable __ro_after_init = true;
 
 static inline
 void print_bind_err_msg(struct thermal_zone_device *tz,
@@ -1065,7 +1069,7 @@ __thermal_cooling_device_register(struct device_node *np,
 	    !ops->set_cur_state)
 		return ERR_PTR(-EINVAL);
 
-	if (!thermal_class)
+	if (thermal_class_unavailable)
 		return ERR_PTR(-ENODEV);
 
 	cdev = kzalloc_obj(*cdev);
@@ -1088,7 +1092,7 @@ __thermal_cooling_device_register(struct device_node *np,
 	cdev->np = np;
 	cdev->ops = ops;
 	cdev->updated = false;
-	cdev->device.class = thermal_class;
+	cdev->device.class = &thermal_class;
 	cdev->devdata = devdata;
 
 	ret = cdev->ops->get_max_state(cdev, &cdev->max_state);
@@ -1536,7 +1540,7 @@ thermal_zone_device_register_with_trips(const char *type,
 	if (polling_delay && passive_delay > polling_delay)
 		return ERR_PTR(-EINVAL);
 
-	if (!thermal_class)
+	if (thermal_class_unavailable)
 		return ERR_PTR(-ENODEV);
 
 	tz = kzalloc_flex(*tz, trips, num_trips);
@@ -1572,7 +1576,7 @@ thermal_zone_device_register_with_trips(const char *type,
 	if (!tz->ops.critical)
 		tz->ops.critical = thermal_zone_device_critical;
 
-	tz->device.class = thermal_class;
+	tz->device.class = &thermal_class;
 	tz->devdata = devdata;
 	tz->num_trips = num_trips;
 	for_each_trip_desc(tz, td) {
@@ -1914,21 +1918,11 @@ static int __init thermal_init(void)
 	if (result)
 		goto destroy_workqueue;
 
-	thermal_class = kzalloc_obj(*thermal_class);
-	if (!thermal_class) {
-		result = -ENOMEM;
+	result = class_register(&thermal_class);
+	if (result)
 		goto unregister_governors;
-	}
 
-	thermal_class->name = "thermal";
-	thermal_class->dev_release = thermal_release;
-
-	result = class_register(thermal_class);
-	if (result) {
-		kfree(thermal_class);
-		thermal_class = NULL;
-		goto unregister_governors;
-	}
+	thermal_class_unavailable = false;
 
 	result = register_pm_notifier(&thermal_pm_nb);
 	if (result)