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,
17				    const struct thermal_trip *trip)
18{
19	int trip_index = thermal_zone_trip_id(tz, trip);
20	struct thermal_instance *instance;
21
22	if (!trip->hysteresis)
23		dev_info_once(&tz->device,
24			      "Zero hysteresis value for thermal zone %s\n", tz->type);
25
26	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
27				trip_index, trip->temperature, tz->temperature,
28				trip->hysteresis);
29
30	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
31		if (instance->trip != trip)
32			continue;
33
34		/* in case fan is in initial state, switch the fan off */
35		if (instance->target == THERMAL_NO_TARGET)
36			instance->target = 0;
37
38		/* in case fan is neither on nor off set the fan to active */
39		if (instance->target != 0 && instance->target != 1) {
40			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
41					instance->name, instance->target);
42			instance->target = 1;
43		}
44
45		/*
46		 * enable fan when temperature exceeds trip_temp and disable
47		 * the fan in case it falls below trip_temp minus hysteresis
48		 */
49		if (instance->target == 0 && tz->temperature >= trip->temperature)
50			instance->target = 1;
51		else if (instance->target == 1 &&
52			 tz->temperature < trip->temperature - trip->hysteresis)
53			instance->target = 0;
54
55		dev_dbg(&instance->cdev->device, "target=%d\n",
56					(int)instance->target);
57
58		mutex_lock(&instance->cdev->lock);
59		instance->cdev->updated = false; /* cdev needs update */
60		mutex_unlock(&instance->cdev->lock);
61	}
62
63	return 0;
64}
65
66/**
67 * bang_bang_control - controls devices associated with the given zone
68 * @tz: thermal_zone_device
69 * @trip: the trip point
70 *
71 * Regulation Logic: a two point regulation, deliver cooling state depending
72 * on the previous state shown in this diagram:
73 *
74 *                Fan:   OFF    ON
75 *
76 *                              |
77 *                              |
78 *          trip_temp:    +---->+
79 *                        |     |        ^
80 *                        |     |        |
81 *                        |     |   Temperature
82 * (trip_temp - hyst):    +<----+
83 *                        |
84 *                        |
85 *                        |
86 *
87 *   * If the fan is not running and temperature exceeds trip_temp, the fan
88 *     gets turned on.
89 *   * In case the fan is running, temperature must fall below
90 *     (trip_temp - hyst) so that the fan gets turned off again.
91 *
92 */
93static int bang_bang_control(struct thermal_zone_device *tz,
94			     const struct thermal_trip *trip)
95{
96	struct thermal_instance *instance;
97	int ret;
98
99	lockdep_assert_held(&tz->lock);
100
101	ret = thermal_zone_trip_update(tz, trip);
102	if (ret)
103		return ret;
104
105	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
106		thermal_cdev_update(instance->cdev);
107
108	return 0;
109}
110
111static struct thermal_governor thermal_gov_bang_bang = {
112	.name		= "bang_bang",
113	.throttle	= bang_bang_control,
114};
115THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
116