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