drivers/thermal/gov_bang_bang.c

   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 <[email protected]>
   6  *
   7  *  Based on step_wise.c with following Copyrights:
   8  *  Copyright (C) 2012 Intel Corp
   9  *  Copyright (C) 2012 Durgadoss R <[email protected]>
  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(&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);