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 
16 static int thermal_zone_trip_update(struct thermal_zone_device *tz, int trip_id)
17 {
18 	struct thermal_trip trip;
19 	struct thermal_instance *instance;
20 	int ret;
21 
22 	ret = __thermal_zone_get_trip(tz, trip_id, &trip);
23 	if (ret) {
24 		pr_warn_once("Failed to retrieve trip point %d\n", trip_id);
25 		return ret;
26 	}
27 
28 	if (!trip.hysteresis)
29 		dev_info_once(&tz->device,
30 			      "Zero hysteresis value for thermal zone %s\n", tz->type);
31 
32 	dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
33 				trip_id, trip.temperature, tz->temperature,
34 				trip.hysteresis);
35 
36 	list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
37 		if (instance->trip != trip_id)
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.temperature)
56 			instance->target = 1;
57 		else if (instance->target == 1 &&
58 			 tz->temperature <= trip.temperature - trip.hysteresis)
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 	return 0;
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  */
99 static int bang_bang_control(struct thermal_zone_device *tz, int trip)
100 {
101 	struct thermal_instance *instance;
102 	int ret;
103 
104 	lockdep_assert_held(&tz->lock);
105 
106 	ret = thermal_zone_trip_update(tz, trip);
107 	if (ret)
108 		return ret;
109 
110 	list_for_each_entry(instance, &tz->thermal_instances, tz_node)
111 		thermal_cdev_update(instance->cdev);
112 
113 	return 0;
114 }
115 
116 static struct thermal_governor thermal_gov_bang_bang = {
117 	.name		= "bang_bang",
118 	.throttle	= bang_bang_control,
119 };
120 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);
121