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 Feuerer <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 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 */
99 static 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
115 static struct thermal_governor thermal_gov_bang_bang = {
116 .name = "bang_bang",
117 .throttle = bang_bang_control,
118 };
119 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);