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
thermal_zone_trip_update(struct thermal_zone_device * tz,int trip_id)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 */
bang_bang_control(struct thermal_zone_device * tz,int trip)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