linux-kernel - [PATCH v1 3/4] thermal: gov_bang

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Message-ID: <8419356.T7Z3S40VBb@rjwysocki.net>
Date: Tue, 13 Aug 2024 16:27:33 +0200
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>, Zhang Rui <rui.zhang@...el.com>,
 Peter Kästle <peter@...e.net>
Subject: [PATCH v1 3/4] thermal: gov_bang_bang: Add .manage() callback

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

After recent changes, the Bang-bang governor may not adjust the
initial configuration of cooling devices to the actual situation.

Namely, if a cooling device bound to a certain trip point starts in
the "on" state and the thermal zone temperature is below the threshold
of that trip point, the trip point may never be crossed on the way up
in which case the state of the cooling device will never be adjusted
because the thermal core will never invoke the governor's
.trip_crossed() callback.  [Note that there is no issue if the zone
temperature is at the trip threshold or above it to start with because
.trip_crossed() will be invoked then to indicate the start of thermal
mitigation for the given trip.]

To address this, add a .manage() callback to the Bang-bang governor
and use it to ensure that all of the thermal instances managed by the
governor have been initialized properly and the states of all of the
cooling devices involved have been adjusted to the current zone
temperature as appropriate.

Fixes: 530c932bdf75 ("thermal: gov_bang_bang: Use .trip_crossed() instead of .throttle()")
Link: https://lore.kernel.org/linux-pm/1bfbbae5-42b0-4c7d-9544-e98855715294@piie.net/
Cc: 6.10+ <stable@...r.kernel.org> # 6.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/thermal/gov_bang_bang.c |   30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

Index: linux-pm/drivers/thermal/gov_bang_bang.c
===================================================================
--- linux-pm.orig/drivers/thermal/gov_bang_bang.c
+++ linux-pm/drivers/thermal/gov_bang_bang.c
@@ -26,6 +26,7 @@ static void bang_bang_set_instance_targe
 	 * when the trip is crossed on the way down.
 	 */
 	instance->target = target;
+	instance->initialized = true;

 	dev_dbg(&instance->cdev->device, "target=%ld\n", instance->target);

@@ -80,8 +81,37 @@ static void bang_bang_control(struct the
 	}
 }

+static void bang_bang_manage(struct thermal_zone_device *tz)
+{
+	const struct thermal_trip_desc *td;
+	struct thermal_instance *instance;
+
+	for_each_trip_desc(tz, td) {
+		const struct thermal_trip *trip = &td->trip;
+
+		if (tz->temperature >= td->threshold ||
+		    trip->temperature == THERMAL_TEMP_INVALID ||
+		    trip->type == THERMAL_TRIP_CRITICAL ||
+		    trip->type == THERMAL_TRIP_HOT)
+			continue;
+
+		/*
+		 * If the initial cooling device state is "on", but the zone
+		 * temperature is not above the trip point, the core will not
+		 * call bang_bang_control() until the zone temperature reaches
+		 * the trip point temperature which may be never.  In those
+		 * cases, set the initial state of the cooling device to 0.
+		 */
+		list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
+			if (!instance->initialized && instance->trip == trip)
+				bang_bang_set_instance_target(instance, 0);
+		}
+	}
+}
+
 static struct thermal_governor thermal_gov_bang_bang = {
 	.name		= "bang_bang",
 	.trip_crossed	= bang_bang_control,
+	.manage		= bang_bang_manage,
 };
 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);