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The bang-bang thermal governor uses a hysteresis to switch abruptly on or off a cooling device. It is intended to control fans, which can not be throttled but just switched on or off. Bang-bang cannot be set as default governor as it is intended for special devices only. For those special devices the driver needs to explicitely request it. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Zhang Rui <rui.zhang@intel.com> Cc: Andreas Mohr <andi@lisas.de> Cc: Borislav Petkov <bp@suse.de> Cc: Javi Merino <javi.merino@arm.com> Cc: linux-pm@vger.kernel.org Signed-off-by: Peter Feuerer <peter@piie.net> Signed-off-by: Zhang Rui <rui.zhang@intel.com>
131 lines
3.6 KiB
C
131 lines
3.6 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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long trip_temp;
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unsigned long 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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tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
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dev_dbg(&tz->device, "Trip%d[temp=%ld]:temp=%d:hyst=%ld\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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