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