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 /**
  17  * bang_bang_control - controls devices associated with the given zone
  18  * @tz: thermal_zone_device
  19  * @trip: the trip point
  20  * @crossed_up: whether or not the trip has been crossed on the way up
  21  *
  22  * Regulation Logic: a two point regulation, deliver cooling state depending
  23  * on the previous state shown in this diagram:
  24  *
  25  *                Fan:   OFF    ON
  26  *
  27  *                              |
  28  *                              |
  29  *          trip_temp:    +---->+
  30  *                        |     |        ^
  31  *                        |     |        |
  32  *                        |     |   Temperature
  33  * (trip_temp - hyst):    +<----+
  34  *                        |
  35  *                        |
  36  *                        |
  37  *
  38  *   * If the fan is not running and temperature exceeds trip_temp, the fan
  39  *     gets turned on.
  40  *   * In case the fan is running, temperature must fall below
  41  *     (trip_temp - hyst) so that the fan gets turned off again.
  42  *
  43  */
  44 static void bang_bang_control(struct thermal_zone_device *tz,
  45                               const struct thermal_trip *trip,
  46                               bool crossed_up)
  47 {
  48         struct thermal_instance *instance;
  49
  50         lockdep_assert_held(&tz->lock);
  51
  52         dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
  53                 thermal_zone_trip_id(tz, trip), trip->temperature,
  54                 tz->temperature, trip->hysteresis);
  55
  56         list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
  57                 if (instance->trip != trip)
  58                         continue;
  59
  60                 if (instance->target == THERMAL_NO_TARGET)
  61                         instance->target = 0;
  62
  63                 if (instance->target != 0 && instance->target != 1) {
  64                         pr_debug("Unexpected state %ld of thermal instance %s in bang-bang\n",
  65                                  instance->target, instance->name);
  66
  67                         instance->target = 1;
  68                 }
  69
  70                 /*
  71                  * Enable the fan when the trip is crossed on the way up and
  72                  * disable it when the trip is crossed on the way down.
  73                  */
  74                 if (instance->target == 0 && crossed_up)
  75                         instance->target = 1;
  76                 else if (instance->target == 1 && !crossed_up)
  77                         instance->target = 0;
  78
  79                 dev_dbg(&instance->cdev->device, "target=%ld\n", instance->target);
  80
  81                 mutex_lock(&instance->cdev->lock);
  82                 instance->cdev->updated = false; /* cdev needs update */
  83                 mutex_unlock(&instance->cdev->lock);
  84         }
  85
  86         list_for_each_entry(instance, &tz->thermal_instances, tz_node)
  87                 thermal_cdev_update(instance->cdev);
  88 }
  89
  90 static struct thermal_governor thermal_gov_bang_bang = {
  91         .name           = "bang_bang",
  92         .trip_crossed   = bang_bang_control,
  93 };
  94 THERMAL_GOVERNOR_DECLARE(thermal_gov_bang_bang);