gov_bang_bang.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 *  gov_bang_bang.c - A simple thermal throttling governor using hysteresis
  4 *
  5 *  Copyright (C) 2014 Peter Kaestle <peter@piie.net>
  6 *
  7 *  Based on step_wise.c with following Copyrights:
  8 *  Copyright (C) 2012 Intel Corp
  9 *  Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
 10 *
 11 * Regulation Logic: a two point regulation, deliver cooling state depending
 12 * on the previous state shown in this diagram:
 13 *
 14 *                Fan:   OFF    ON
 15 *
 16 *                              |
 17 *                              |
 18 *          trip_temp:    +---->+
 19 *                        |     |        ^
 20 *                        |     |        |
 21 *                        |     |   Temperature
 22 * (trip_temp - hyst):    +<----+
 23 *                        |
 24 *                        |
 25 *                        |
 26 *
 27 *   * If the fan is not running and temperature exceeds trip_temp, the fan
 28 *     gets turned on.
 29 *   * In case the fan is running, temperature must fall below
 30 *     (trip_temp - hyst) so that the fan gets turned off again.
 31 */
 32
 33#include <linux/thermal.h>
 34
 35#include "thermal_core.h"
 36
 37static void bang_bang_set_instance_target(struct thermal_instance *instance,
 38					  unsigned int target)
 39{
 40	if (instance->target != 0 && instance->target != 1 &&
 41	    instance->target != THERMAL_NO_TARGET)
 42		pr_debug("Unexpected state %ld of thermal instance %s in bang-bang\n",
 43			 instance->target, instance->name);
 44
 45	/*
 46	 * Enable the fan when the trip is crossed on the way up and disable it
 47	 * when the trip is crossed on the way down.
 48	 */
 49	instance->target = target;
 50	instance->initialized = true;
 51
 52	dev_dbg(&instance->cdev->device, "target=%ld\n", instance->target);
 53
 54	thermal_cdev_update_nocheck(instance->cdev);
 55}
 56
 57/**
 58 * bang_bang_trip_crossed - controls devices associated with the given zone
 59 * @tz: thermal_zone_device
 60 * @trip: the trip point
 61 * @upward: whether or not the trip has been crossed on the way up
 62 */
 63static void bang_bang_trip_crossed(struct thermal_zone_device *tz,
 64				   const struct thermal_trip *trip,
 65				   bool upward)
 66{
 67	const struct thermal_trip_desc *td = trip_to_trip_desc(trip);
 68	struct thermal_instance *instance;
 69
 70	lockdep_assert_held(&tz->lock);
 71
 72	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
 73		thermal_zone_trip_id(tz, trip), trip->temperature,
 74		tz->temperature, trip->hysteresis);
 75
 76	list_for_each_entry(instance, &td->thermal_instances, trip_node)
 77		bang_bang_set_instance_target(instance, upward);
 78}
 79
 80static void bang_bang_manage(struct thermal_zone_device *tz)
 81{
 82	const struct thermal_trip_desc *td;
 83	struct thermal_instance *instance;
 84
 85	/* If the code below has run already, nothing needs to be done. */
 86	if (tz->governor_data)
 87		return;
 88
 89	for_each_trip_desc(tz, td) {
 90		const struct thermal_trip *trip = &td->trip;
 91		bool turn_on;
 92
 93		if (trip->temperature == THERMAL_TEMP_INVALID ||
 94		    trip->type == THERMAL_TRIP_CRITICAL ||
 95		    trip->type == THERMAL_TRIP_HOT)
 96			continue;
 97
 98		/*
 99		 * Adjust the target states for uninitialized thermal instances
100		 * to the thermal zone temperature and the trip point threshold.
101		 */
102		turn_on = tz->temperature >= td->threshold;
103		list_for_each_entry(instance, &td->thermal_instances, trip_node) {
104			if (!instance->initialized)
105				bang_bang_set_instance_target(instance, turn_on);
106		}
107	}
108
109	tz->governor_data = (void *)true;
110}
111
112static void bang_bang_update_tz(struct thermal_zone_device *tz,
113				enum thermal_notify_event reason)
114{
115	/*
116	 * Let bang_bang_manage() know that it needs to walk trips after binding
117	 * a new cdev and after system resume.
118	 */
119	if (reason == THERMAL_TZ_BIND_CDEV || reason == THERMAL_TZ_RESUME)
120		tz->governor_data = NULL;
121}
122
123static struct thermal_governor thermal_gov_bang_bang = {
124	.name		= "bang_bang",
125	.trip_crossed	= bang_bang_trip_crossed,
126	.manage		= bang_bang_manage,
127	.update_tz	= bang_bang_update_tz,
128};
129THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);