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