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         int trip_temp, trip_hyst;
  29         struct thermal_instance *instance;
  30
  31         tz->ops->get_trip_temp(tz, trip, &trip_temp);
  32         tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
  33
  34         dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
  35                                 trip, trip_temp, tz->temperature,
  36                                 trip_hyst);
  37
  38         mutex_lock(&tz->lock);
  39
  40         list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
  41                 if (instance->trip != trip)
  42                         continue;
  43
  44                 /* in case fan is in initial state, switch the fan off */
  45                 if (instance->target == THERMAL_NO_TARGET)
  46                         instance->target = 0;
  47
  48                 /* in case fan is neither on nor off set the fan to active */
  49                 if (instance->target != 0 && instance->target != 1) {
  50                         pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
  51                                         instance->name, instance->target);
  52                         instance->target = 1;
  53                 }
  54
  55                 /*
  56                  * enable fan when temperature exceeds trip_temp and disable
  57                  * the fan in case it falls below trip_temp minus hysteresis
  58                  */
  59                 if (instance->target == 0 && tz->temperature >= trip_temp)
  60                         instance->target = 1;
  61                 else if (instance->target == 1 &&
  62                                 tz->temperature < trip_temp - trip_hyst)
  63                         instance->target = 0;
  64
  65                 dev_dbg(&instance->cdev->device, "target=%d\n",
  66                                         (int)instance->target);
  67
  68                 instance->cdev->updated = false; /* cdev needs update */
  69         }
  70
  71         mutex_unlock(&tz->lock);
  72 }
  73
  74 /**
  75  * bang_bang_control - controls devices associated with the given zone
  76  * @tz - thermal_zone_device
  77  * @trip - the trip point
  78  *
  79  * Regulation Logic: a two point regulation, deliver cooling state depending
  80  * on the previous state shown in this diagram:
  81  *
  82  *                Fan:   OFF    ON
  83  *
  84  *                              |
  85  *                              |
  86  *          trip_temp:    +---->+
  87  *                        |     |        ^
  88  *                        |     |        |
  89  *                        |     |   Temperature
  90  * (trip_temp - hyst):    +<----+
  91  *                        |
  92  *                        |
  93  *                        |
  94  *
  95  *   * If the fan is not running and temperature exceeds trip_temp, the fan
  96  *     gets turned on.
  97  *   * In case the fan is running, temperature must fall below
  98  *     (trip_temp - hyst) so that the fan gets turned off again.
  99  *
 100  */
 101 static int bang_bang_control(struct thermal_zone_device *tz, int trip)
 102 {
 103         struct thermal_instance *instance;
 104
 105         thermal_zone_trip_update(tz, trip);
 106
 107         mutex_lock(&tz->lock);
 108
 109         list_for_each_entry(instance, &tz->thermal_instances, tz_node)
 110                 thermal_cdev_update(instance->cdev);
 111
 112         mutex_unlock(&tz->lock);
 113
 114         return 0;
 115 }
 116
 117 static struct thermal_governor thermal_gov_bang_bang = {
 118         .name           = "bang_bang",
 119         .throttle       = bang_bang_control,
 120 };
 121
 122 int thermal_gov_bang_bang_register(void)
 123 {
 124         return thermal_register_governor(&thermal_gov_bang_bang);
 125 }
 126
 127 void thermal_gov_bang_bang_unregister(void)
 128 {
 129         thermal_unregister_governor(&thermal_gov_bang_bang);
 130 }