![Michele Di Giorgio](/assets/img/avatar_default.png)
Bang-bang thermal governor uses trip point hysteresis to make decisions. Hysteresis is a required property in the device tree for trip points, but it is an optional thermal zone device operation. Hence, we need to check whether the function pointer is valid or not. If it is not available, we assume the hysteresis to be zero. Consequently, a highly varying temperature will make the governor continuosly switch a cooling device ON and OFF. CC: Zhang Rui <rui.zhang@intel.com> CC: Eduardo Valentin <edubezval@gmail.com> CC: Peter Feuerer <peter@piie.net> Signed-off-by: Michele Di Giorgio <michele.digiorgio@arm.com> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
137 lines
3.8 KiB
C
137 lines
3.8 KiB
C
/*
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* gov_bang_bang.c - A simple thermal throttling governor using hysteresis
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*
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* Copyright (C) 2014 Peter Feuerer <peter@piie.net>
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*
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* Based on step_wise.c with following Copyrights:
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* Copyright (C) 2012 Intel Corp
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* Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
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*
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 2.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
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* the GNU General Public License for more details.
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*
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*/
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#include <linux/thermal.h>
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#include "thermal_core.h"
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static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
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{
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int trip_temp, trip_hyst;
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struct thermal_instance *instance;
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tz->ops->get_trip_temp(tz, trip, &trip_temp);
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if (!tz->ops->get_trip_hyst) {
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pr_warn_once("Undefined get_trip_hyst for thermal zone %s - "
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"running with default hysteresis zero\n", tz->type);
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trip_hyst = 0;
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} else
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tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
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dev_dbg(&tz->device, "Trip%d[temp=%d]:temp=%d:hyst=%d\n",
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trip, trip_temp, tz->temperature,
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trip_hyst);
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mutex_lock(&tz->lock);
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list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
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if (instance->trip != trip)
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continue;
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/* in case fan is in initial state, switch the fan off */
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if (instance->target == THERMAL_NO_TARGET)
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instance->target = 0;
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/* in case fan is neither on nor off set the fan to active */
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if (instance->target != 0 && instance->target != 1) {
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pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
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instance->name, instance->target);
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instance->target = 1;
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}
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/*
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* enable fan when temperature exceeds trip_temp and disable
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* the fan in case it falls below trip_temp minus hysteresis
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*/
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if (instance->target == 0 && tz->temperature >= trip_temp)
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instance->target = 1;
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else if (instance->target == 1 &&
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tz->temperature < trip_temp - trip_hyst)
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instance->target = 0;
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dev_dbg(&instance->cdev->device, "target=%d\n",
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(int)instance->target);
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instance->cdev->updated = false; /* cdev needs update */
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}
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mutex_unlock(&tz->lock);
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}
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/**
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* bang_bang_control - controls devices associated with the given zone
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* @tz - thermal_zone_device
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* @trip - the trip point
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*
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* Regulation Logic: a two point regulation, deliver cooling state depending
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* on the previous state shown in this diagram:
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*
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* Fan: OFF ON
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*
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* |
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* |
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* trip_temp: +---->+
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* | | ^
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* | | |
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* | | Temperature
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* (trip_temp - hyst): +<----+
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* |
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* |
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* |
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*
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* * If the fan is not running and temperature exceeds trip_temp, the fan
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* gets turned on.
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* * In case the fan is running, temperature must fall below
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* (trip_temp - hyst) so that the fan gets turned off again.
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*
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*/
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static int bang_bang_control(struct thermal_zone_device *tz, int trip)
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{
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struct thermal_instance *instance;
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thermal_zone_trip_update(tz, trip);
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mutex_lock(&tz->lock);
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list_for_each_entry(instance, &tz->thermal_instances, tz_node)
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thermal_cdev_update(instance->cdev);
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mutex_unlock(&tz->lock);
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return 0;
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}
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static struct thermal_governor thermal_gov_bang_bang = {
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.name = "bang_bang",
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.throttle = bang_bang_control,
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};
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int thermal_gov_bang_bang_register(void)
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{
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return thermal_register_governor(&thermal_gov_bang_bang);
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}
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void thermal_gov_bang_bang_unregister(void)
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{
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thermal_unregister_governor(&thermal_gov_bang_bang);
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}
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