[PATCH v2 3/3] thermal: core: Sort trip point crossing notifications by temperature

[Rafael J. Wysocki]

From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

If multiple trip points are crossed in one go and the trips table in
the thermal zone device object is not sorted, the corresponding trip
point crossing notifications sent to user space will not be ordered
either.

Moreover, if the trips table is sorted by trip temperature in ascending
order, the trip crossing notifications on the way up will be sent in that
order too, but the trip crossing notifications on the way down will be
sent in the reverse order.

This is generally confusing and it is better to make the kernel send the
notifications in the order of growing (on the way up) or falling (on the
way down) trip temperature.

To achieve that, instead of sending a trip crossing notification right
away from handle_thermal_trip(), put the trip in question on a list that
will be sorted by __thermal_zone_device_update() after processing all of
the trips and before sending the notifications.

Do the same with the debugfs recording of trip crossing events.

Link: https://lore.kernel.org/linux-pm/20240306085428.88011-1-daniel.lezcano@xxxxxxxxxx/
Reported-by: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> 
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
---
 drivers/thermal/thermal_core.c |   39 +++++++++++++++++++++++++++++++++------
 drivers/thermal/thermal_core.h |    1 +
 2 files changed, 34 insertions(+), 6 deletions(-)

Index: linux-pm/drivers/thermal/thermal_core.c
===================================================================
--- linux-pm.orig/drivers/thermal/thermal_core.c
+++ linux-pm/drivers/thermal/thermal_core.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/kdev_t.h>
 #include <linux/idr.h>
+#include <linux/list_sort.h>
 #include <linux/thermal.h>
 #include <linux/reboot.h>
 #include <linux/string.h>
@@ -361,7 +362,9 @@ static void handle_critical_trips(struct
 }
 
 static void handle_thermal_trip(struct thermal_zone_device *tz,
-				struct thermal_trip_desc *td)
+				struct thermal_trip_desc *td,
+				struct list_head *way_up_list,
+				struct list_head *way_down_list)
 {
 	const struct thermal_trip *trip = &td->trip;
 
@@ -382,8 +385,7 @@ static void handle_thermal_trip(struct t
 		 * the threshold and the trip temperature will be equal.
 		 */
 		if (tz->temperature >= trip->temperature) {
-			thermal_notify_tz_trip_up(tz, trip);
-			thermal_debug_tz_trip_up(tz, trip);
+			list_add_tail(&td->notify_list_node, way_up_list);
 			td->threshold = trip->temperature - trip->hysteresis;
 		} else {
 			td->threshold = trip->temperature;
@@ -400,8 +402,7 @@ static void handle_thermal_trip(struct t
 		 * the trip.
 		 */
 		if (tz->temperature < trip->temperature - trip->hysteresis) {
-			thermal_notify_tz_trip_down(tz, trip);
-			thermal_debug_tz_trip_down(tz, trip);
+			list_add(&td->notify_list_node, way_down_list);
 			td->threshold = trip->temperature;
 		} else {
 			td->threshold = trip->temperature - trip->hysteresis;
@@ -457,10 +458,24 @@ static void thermal_zone_device_init(str
 		pos->initialized = false;
 }
 
+static int thermal_trip_notify_cmp(void *ascending, const struct list_head *a,
+				   const struct list_head *b)
+{
+	struct thermal_trip_desc *tda = container_of(a, struct thermal_trip_desc,
+						     notify_list_node);
+	struct thermal_trip_desc *tdb = container_of(b, struct thermal_trip_desc,
+						     notify_list_node);
+	int ret = tdb->trip.temperature - tda->trip.temperature;
+
+	return ascending ? ret : -ret;
+}
+
 void __thermal_zone_device_update(struct thermal_zone_device *tz,
 				  enum thermal_notify_event event)
 {
 	struct thermal_trip_desc *td;
+	LIST_HEAD(way_down_list);
+	LIST_HEAD(way_up_list);
 
 	if (tz->suspended)
 		return;
@@ -475,7 +490,19 @@ void __thermal_zone_device_update(struct
 	tz->notify_event = event;
 
 	for_each_trip_desc(tz, td)
-		handle_thermal_trip(tz, td);
+		handle_thermal_trip(tz, td, &way_up_list, &way_down_list);
+
+	list_sort((void *)true, &way_up_list, thermal_trip_notify_cmp);
+	list_for_each_entry(td, &way_up_list, notify_list_node) {
+		thermal_notify_tz_trip_up(tz, &td->trip);
+		thermal_debug_tz_trip_up(tz, &td->trip);
+	}
+
+	list_sort(NULL, &way_down_list, thermal_trip_notify_cmp);
+	list_for_each_entry(td, &way_down_list, notify_list_node) {
+		thermal_notify_tz_trip_down(tz, &td->trip);
+		thermal_debug_tz_trip_down(tz, &td->trip);
+	}
 
 	monitor_thermal_zone(tz);
 }
Index: linux-pm/drivers/thermal/thermal_core.h
===================================================================
--- linux-pm.orig/drivers/thermal/thermal_core.h
+++ linux-pm/drivers/thermal/thermal_core.h
@@ -17,6 +17,7 @@
 
 struct thermal_trip_desc {
 	struct thermal_trip trip;
+	struct list_head notify_list_node;
 	int threshold;
 };