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 void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
17{
18	int trip_temp, trip_hyst;
19	struct thermal_instance *instance;
20
21	tz->ops->get_trip_temp(tz, trip, &trip_temp);
22
23	if (!tz->ops->get_trip_hyst) {
24		pr_warn_once("Undefined get_trip_hyst for thermal zone %s - "
25				"running with default hysteresis zero\n", tz->type);
26		trip_hyst = 0;
27	} else
28		tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
29
30	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
31				trip, trip_temp, tz->temperature,
32				trip_hyst);
33
34	mutex_lock(&tz->lock);
35
36	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
37		if (instance->trip != trip)
38			continue;
39
40		/* in case fan is in initial state, switch the fan off */
41		if (instance->target == THERMAL_NO_TARGET)
42			instance->target = 0;
43
44		/* in case fan is neither on nor off set the fan to active */
45		if (instance->target != 0 && instance->target != 1) {
46			pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
47					instance->name, instance->target);
48			instance->target = 1;
49		}
50
51		/*
52		 * enable fan when temperature exceeds trip_temp and disable
53		 * the fan in case it falls below trip_temp minus hysteresis
54		 */
55		if (instance->target == 0 && tz->temperature >= trip_temp)
56			instance->target = 1;
57		else if (instance->target == 1 &&
58				tz->temperature <= trip_temp - trip_hyst)
59			instance->target = 0;
60
61		dev_dbg(&instance->cdev->device, "target=%d\n",
62					(int)instance->target);
63
64		mutex_lock(&instance->cdev->lock);
65		instance->cdev->updated = false; /* cdev needs update */
66		mutex_unlock(&instance->cdev->lock);
67	}
68
69	mutex_unlock(&tz->lock);
70}
71
72/**
73 * bang_bang_control - controls devices associated with the given zone
74 * @tz: thermal_zone_device
75 * @trip: the trip point
76 *
77 * Regulation Logic: a two point regulation, deliver cooling state depending
78 * on the previous state shown in this diagram:
79 *
80 *                Fan:   OFF    ON
81 *
82 *                              |
83 *                              |
84 *          trip_temp:    +---->+
85 *                        |     |        ^
86 *                        |     |        |
87 *                        |     |   Temperature
88 * (trip_temp - hyst):    +<----+
89 *                        |
90 *                        |
91 *                        |
92 *
93 *   * If the fan is not running and temperature exceeds trip_temp, the fan
94 *     gets turned on.
95 *   * In case the fan is running, temperature must fall below
96 *     (trip_temp - hyst) so that the fan gets turned off again.
97 *
98 */
99static int bang_bang_control(struct thermal_zone_device *tz, int trip)
100{
101	struct thermal_instance *instance;
102
103	thermal_zone_trip_update(tz, trip);
104
105	mutex_lock(&tz->lock);
106
107	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
108		thermal_cdev_update(instance->cdev);
109
110	mutex_unlock(&tz->lock);
111
112	return 0;
113}
114
115static struct thermal_governor thermal_gov_bang_bang = {
116	.name		= "bang_bang",
117	.throttle	= bang_bang_control,
118};
119THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
120