thermal: gov_bang_bang: Use governor_data to reduce overhead

After running once, the for_each_trip_desc() loop in
bang_bang_manage() is pure needless overhead because it is not going to
make any changes unless a new cooling device has been bound to one of
the trips in the thermal zone or the system is resuming from sleep.

For this reason, make bang_bang_manage() set governor_data for the
thermal zone and check it upfront to decide whether or not it needs to
do anything.

However, governor_data needs to be reset in some cases to let
bang_bang_manage() know that it should walk the trips again, so add an
.update_tz() callback to the governor and make the core additionally
invoke it during system resume.

To avoid affecting the other users of that callback unnecessarily, add
a special notification reason for system resume, THERMAL_TZ_RESUME, and
also pass it to __thermal_zone_device_update() called during system
resume for consistency.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Kästle <peter@piie.net>
Reviewed-by: Zhang Rui <rui.zhang@intel.com>
Cc: 6.10+ <stable@vger.kernel.org> # 6.10+
Link: https://patch.msgid.link/2285575.iZASKD2KPV@rjwysocki.net

drivers/thermal/gov_bang_bang.c

@@ -86,6 +86,10 @@ static void bang_bang_manage(struct thermal_zone_device *tz)
 	const struct thermal_trip_desc *td;
 	struct thermal_instance *instance;
 
+	/* If the code below has run already, nothing needs to be done. */
+	if (tz->governor_data)
+		return;
+
 	for_each_trip_desc(tz, td) {
 		const struct thermal_trip *trip = &td->trip;
 
@@ -107,11 +111,25 @@ static void bang_bang_manage(struct thermal_zone_device *tz)
 				bang_bang_set_instance_target(instance, 0);
 		}
 	}
+
+	tz->governor_data = (void *)true;
+}
+
+static void bang_bang_update_tz(struct thermal_zone_device *tz,
+				enum thermal_notify_event reason)
+{
+	/*
+	 * Let bang_bang_manage() know that it needs to walk trips after binding
+	 * a new cdev and after system resume.
+	 */
+	if (reason == THERMAL_TZ_BIND_CDEV || reason == THERMAL_TZ_RESUME)
+		tz->governor_data = NULL;
 }
 
 static struct thermal_governor thermal_gov_bang_bang = {
 	.name		= "bang_bang",
 	.trip_crossed	= bang_bang_control,
 	.manage		= bang_bang_manage,
+	.update_tz	= bang_bang_update_tz,
 };
 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);

drivers/thermal/thermal_core.c

@@ -1728,7 +1728,8 @@ static void thermal_zone_device_resume(struct work_struct *work)
 
 	thermal_debug_tz_resume(tz);
 	thermal_zone_device_init(tz);
-	__thermal_zone_device_update(tz, THERMAL_EVENT_UNSPECIFIED);
+	thermal_governor_update_tz(tz, THERMAL_TZ_RESUME);
+	__thermal_zone_device_update(tz, THERMAL_TZ_RESUME);
 
 	complete(&tz->resume);
 	tz->resuming = false;

include/linux/thermal.h

@@ -55,6 +55,7 @@ enum thermal_notify_event {
 	THERMAL_TZ_BIND_CDEV, /* Cooling dev is bind to the thermal zone */
 	THERMAL_TZ_UNBIND_CDEV, /* Cooling dev is unbind from the thermal zone */
 	THERMAL_INSTANCE_WEIGHT_CHANGED, /* Thermal instance weight changed */
+	THERMAL_TZ_RESUME, /* Thermal zone is resuming after system sleep */
 };
 
 /**