drivers/thermal/gov_bang_bang.c

   1 /*
   2  *  gov_bang_bang.c - A simple thermal throttling governor using hysteresis
   3  *
   4  *  Copyright (C) 2014 Peter Feuerer <peter@piie.net>
   5  *
   6  *  Based on step_wise.c with following Copyrights:
   7  *  Copyright (C) 2012 Intel Corp
   8  *  Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
   9  *
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License as published by
  13  * the Free Software Foundation, version 2.
  14  *
  15  * This program is distributed in the hope that it will be useful,
  16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
  18  * the GNU General Public License for more details.
  19  *
  20  */
  21
  22 #include <linux/thermal.h>
  23
  24 #include "thermal_core.h"
  25
  26 static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
  27 {
  28         long trip_temp;
  29         unsigned long trip_hyst;
  30         struct thermal_instance *instance;
  31
  32         tz->ops->get_trip_temp(tz, trip, &trip_temp);
  33         tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
  34
  35         dev_dbg(&tz->device, "Trip%d[temp=%ld]:temp=%d:hyst=%ld\n",
  36                                 trip, trip_temp, tz->temperature,
  37                                 trip_hyst);
  38
  39         mutex_lock(&tz->lock);
  40
  41         list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
  42                 if (instance->trip != trip)
  43                         continue;
  44
  45                 /* in case fan is in initial state, switch the fan off */
  46                 if (instance->target == THERMAL_NO_TARGET)
  47                         instance->target = 0;
  48
  49                 /* in case fan is neither on nor off set the fan to active */
  50                 if (instance->target != 0 && instance->target != 1) {
  51                         pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
  52                                         instance->name, instance->target);
  53                         instance->target = 1;
  54                 }
  55
  56                 /*
  57                  * enable fan when temperature exceeds trip_temp and disable
  58                  * the fan in case it falls below trip_temp minus hysteresis
  59                  */
  60                 if (instance->target == 0 && tz->temperature >= trip_temp)
  61                         instance->target = 1;
  62                 else if (instance->target == 1 &&
  63                                 tz->temperature < trip_temp - trip_hyst)
  64                         instance->target = 0;
  65
  66                 dev_dbg(&instance->cdev->device, "target=%d\n",
  67                                         (int)instance->target);
  68
  69                 instance->cdev->updated = false; /* cdev needs update */
  70         }
  71
  72         mutex_unlock(&tz->lock);
  73 }
  74
  75 /**
  76  * bang_bang_control - controls devices associated with the given zone
  77  * @tz - thermal_zone_device
  78  * @trip - the trip point
  79  *
  80  * Regulation Logic: a two point regulation, deliver cooling state depending
  81  * on the previous state shown in this diagram:
  82  *
  83  *                Fan:   OFF    ON
  84  *
  85  *                              |
  86  *                              |
  87  *          trip_temp:    +---->+
  88  *                        |     |        ^
  89  *                        |     |        |
  90  *                        |     |   Temperature
  91  * (trip_temp - hyst):    +<----+
  92  *                        |
  93  *                        |
  94  *                        |
  95  *
  96  *   * If the fan is not running and temperature exceeds trip_temp, the fan
  97  *     gets turned on.
  98  *   * In case the fan is running, temperature must fall below
  99  *     (trip_temp - hyst) so that the fan gets turned off again.
 100  *
 101  */
 102 static int bang_bang_control(struct thermal_zone_device *tz, int trip)
 103 {
 104         struct thermal_instance *instance;
 105
 106         thermal_zone_trip_update(tz, trip);
 107
 108         mutex_lock(&tz->lock);
 109
 110         list_for_each_entry(instance, &tz->thermal_instances, tz_node)
 111                 thermal_cdev_update(instance->cdev);
 112
 113         mutex_unlock(&tz->lock);
 114
 115         return 0;
 116 }
 117
 118 static struct thermal_governor thermal_gov_bang_bang = {
 119         .name           = "bang_bang",
 120         .throttle       = bang_bang_control,
 121 };
 122
 123 int thermal_gov_bang_bang_register(void)
 124 {
 125         return thermal_register_governor(&thermal_gov_bang_bang);
 126 }
 127
 128 void thermal_gov_bang_bang_unregister(void)
 129 {
 130         thermal_unregister_governor(&thermal_gov_bang_bang);
 131 }