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/*
* gov_bang_bang.c - A simple thermal throttling governor using hysteresis
*
* Copyright (C) 2014 Peter Feuerer <peter@piie.net>
*
* Based on step_wise.c with following Copyrights:
* Copyright (C) 2012 Intel Corp
* Copyright (C) 2012 Durgadoss R <durgadoss.r@intel.com>
*
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 2.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See
* the GNU General Public License for more details.
*
*/
#include <linux/thermal.h>
#include "thermal_core.h"
static void thermal_zone_trip_update(struct thermal_zone_device *tz, int trip)
{
long trip_temp;
unsigned long trip_hyst;
struct thermal_instance *instance;
tz->ops->get_trip_temp(tz, trip, &trip_temp);
tz->ops->get_trip_hyst(tz, trip, &trip_hyst);
dev_dbg(&tz->device, "Trip%d[temp=%ld]:temp=%d:hyst=%ld\n",
trip, trip_temp, tz->temperature,
trip_hyst);
mutex_lock(&tz->lock);
list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
if (instance->trip != trip)
continue;
/* in case fan is in initial state, switch the fan off */
if (instance->target == THERMAL_NO_TARGET)
instance->target = 0;
/* in case fan is neither on nor off set the fan to active */
if (instance->target != 0 && instance->target != 1) {
pr_warn("Thermal instance %s controlled by bang-bang has unexpected state: %ld\n",
instance->name, instance->target);
instance->target = 1;
}
/*
* enable fan when temperature exceeds trip_temp and disable
* the fan in case it falls below trip_temp minus hysteresis
*/
if (instance->target == 0 && tz->temperature >= trip_temp)
instance->target = 1;
else if (instance->target == 1 &&
tz->temperature < trip_temp - trip_hyst)
instance->target = 0;
dev_dbg(&instance->cdev->device, "target=%d\n",
(int)instance->target);
instance->cdev->updated = false; /* cdev needs update */
}
mutex_unlock(&tz->lock);
}
/**
* bang_bang_control - controls devices associated with the given zone
* @tz - thermal_zone_device
* @trip - the trip point
*
* Regulation Logic: a two point regulation, deliver cooling state depending
* on the previous state shown in this diagram:
*
* Fan: OFF ON
*
* |
* |
* trip_temp: +---->+
* | | ^
* | | |
* | | Temperature
* (trip_temp - hyst): +<----+
* |
* |
* |
*
* * If the fan is not running and temperature exceeds trip_temp, the fan
* gets turned on.
* * In case the fan is running, temperature must fall below
* (trip_temp - hyst) so that the fan gets turned off again.
*
*/
static int bang_bang_control(struct thermal_zone_device *tz, int trip)
{
struct thermal_instance *instance;
thermal_zone_trip_update(tz, trip);
mutex_lock(&tz->lock);
list_for_each_entry(instance, &tz->thermal_instances, tz_node)
thermal_cdev_update(instance->cdev);
mutex_unlock(&tz->lock);
return 0;
}
static struct thermal_governor thermal_gov_bang_bang = {
.name = "bang_bang",
.throttle = bang_bang_control,
};
int thermal_gov_bang_bang_register(void)
{
return thermal_register_governor(&thermal_gov_bang_bang);
}
void thermal_gov_bang_bang_unregister(void)
{
thermal_unregister_governor(&thermal_gov_bang_bang);
}
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