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
12#include <linux/thermal.h>
13
14#include "thermal_core.h"
15
16static int thermal_zone_trip_update(struct thermal_zone_device *tz, int trip_index)
17{
18	const struct thermal_trip *trip = &tz->trips[trip_index];
19	struct thermal_instance *instance;
20
21	if (!trip->hysteresis)
22		dev_info_once(&tz->device,
23			      "Zero hysteresis value for thermal zone %s\n", tz->type);
24
25	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
26				trip_index, trip->temperature, tz->temperature,
27				trip->hysteresis);
28
29	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
30		if (instance->trip != trip)
31			continue;
32
33		/* in case fan is in initial state, switch the fan off */
34		if (instance->target == THERMAL_NO_TARGET)
35			instance->target = 0;
36
37		/* in case fan is neither on nor off set the fan to active */
38		if (instance->target != 0 && instance->target != 1) {
39			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
40					instance->name, instance->target);
41			instance->target = 1;
42		}
43
44		/*
45		 * enable fan when temperature exceeds trip_temp and disable
46		 * the fan in case it falls below trip_temp minus hysteresis
47		 */
48		if (instance->target == 0 && tz->temperature >= trip->temperature)
49			instance->target = 1;
50		else if (instance->target == 1 &&
51			 tz->temperature <= trip->temperature - trip->hysteresis)
52			instance->target = 0;
53
54		dev_dbg(&instance->cdev->device, "target=%d\n",
55					(int)instance->target);
56
57		mutex_lock(&instance->cdev->lock);
58		instance->cdev->updated = false; /* cdev needs update */
59		mutex_unlock(&instance->cdev->lock);
60	}
61
62	return 0;
63}
64
65/**
66 * bang_bang_control - controls devices associated with the given zone
67 * @tz: thermal_zone_device
68 * @trip: the trip point
69 *
70 * Regulation Logic: a two point regulation, deliver cooling state depending
71 * on the previous state shown in this diagram:
72 *
73 *                Fan:   OFF    ON
74 *
75 *                              |
76 *                              |
77 *          trip_temp:    +---->+
78 *                        |     |        ^
79 *                        |     |        |
80 *                        |     |   Temperature
81 * (trip_temp - hyst):    +<----+
82 *                        |
83 *                        |
84 *                        |
85 *
86 *   * If the fan is not running and temperature exceeds trip_temp, the fan
87 *     gets turned on.
88 *   * In case the fan is running, temperature must fall below
89 *     (trip_temp - hyst) so that the fan gets turned off again.
90 *
91 */
92static int bang_bang_control(struct thermal_zone_device *tz, int trip)
93{
94	struct thermal_instance *instance;
95	int ret;
96
97	lockdep_assert_held(&tz->lock);
98
99	ret = thermal_zone_trip_update(tz, trip);
100	if (ret)
101		return ret;
102
103	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
104		thermal_cdev_update(instance->cdev);
105
106	return 0;
107}
108
109static struct thermal_governor thermal_gov_bang_bang = {
110	.name		= "bang_bang",
111	.throttle	= bang_bang_control,
112};
113THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
114