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/*
* A power allocator to manage temperature
*
* Copyright (C) 2014 ARM Ltd.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed "as is" WITHOUT ANY WARRANTY of any
* kind, whether express or implied; without even the implied warranty
* of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
#define pr_fmt(fmt) "Power allocator: " fmt
#include <linux/rculist.h>
#include <linux/slab.h>
#include <linux/thermal.h>
#define CREATE_TRACE_POINTS
#include <trace/events/thermal_power_allocator.h>
#include "thermal_core.h"
#define FRAC_BITS 10
#define int_to_frac(x) ((x) << FRAC_BITS)
#define frac_to_int(x) ((x) >> FRAC_BITS)
/**
* mul_frac() - multiply two fixed-point numbers
* @x: first multiplicand
* @y: second multiplicand
*
* Return: the result of multiplying two fixed-point numbers. The
* result is also a fixed-point number.
*/
static inline s64 mul_frac(s64 x, s64 y)
{
return (x * y) >> FRAC_BITS;
}
/**
* div_frac() - divide two fixed-point numbers
* @x: the dividend
* @y: the divisor
*
* Return: the result of dividing two fixed-point numbers. The
* result is also a fixed-point number.
*/
static inline s64 div_frac(s64 x, s64 y)
{
return div_s64(x << FRAC_BITS, y);
}
/**
* struct power_allocator_params - parameters for the power allocator governor
* @err_integral: accumulated error in the PID controller.
* @prev_err: error in the previous iteration of the PID controller.
* Used to calculate the derivative term.
* @trip_switch_on: first passive trip point of the thermal zone. The
* governor switches on when this trip point is crossed.
* @trip_max_desired_temperature: last passive trip point of the thermal
* zone. The temperature we are
* controlling for.
*/
struct power_allocator_params {
s64 err_integral;
s32 prev_err;
int trip_switch_on;
int trip_max_desired_temperature;
};
/**
* pid_controller() - PID controller
* @tz: thermal zone we are operating in
* @current_temp: the current temperature in millicelsius
* @control_temp: the target temperature in millicelsius
* @max_allocatable_power: maximum allocatable power for this thermal zone
*
* This PID controller increases the available power budget so that the
* temperature of the thermal zone gets as close as possible to
* @control_temp and limits the power if it exceeds it. k_po is the
* proportional term when we are overshooting, k_pu is the
* proportional term when we are undershooting. integral_cutoff is a
* threshold below which we stop accumulating the error. The
* accumulated error is only valid if the requested power will make
* the system warmer. If the system is mostly idle, there's no point
* in accumulating positive error.
*
* Return: The power budget for the next period.
*/
static u32 pid_controller(struct thermal_zone_device *tz,
unsigned long current_temp,
unsigned long control_temp,
u32 max_allocatable_power)
{
s64 p, i, d, power_range;
s32 err, max_power_frac;
struct power_allocator_params *params = tz->governor_data;
max_power_frac = int_to_frac(max_allocatable_power);
err = ((s32)control_temp - (s32)current_temp);
err = int_to_frac(err);
/* Calculate the proportional term */
p = mul_frac(err < 0 ? tz->tzp->k_po : tz->tzp->k_pu, err);
/*
* Calculate the integral term
*
* if the error is less than cut off allow integration (but
* the integral is limited to max power)
*/
i = mul_frac(tz->tzp->k_i, params->err_integral);
if (err < int_to_frac(tz->tzp->integral_cutoff)) {
s64 i_next = i + mul_frac(tz->tzp->k_i, err);
if (abs64(i_next) < max_power_frac) {
i = i_next;
params->err_integral += err;
}
}
/*
* Calculate the derivative term
*
* We do err - prev_err, so with a positive k_d, a decreasing
* error (i.e. driving closer to the line) results in less
* power being applied, slowing down the controller)
*/
d = mul_frac(tz->tzp->k_d, err - params->prev_err);
d = div_frac(d, tz->passive_delay);
params->prev_err = err;
power_range = p + i + d;
/* feed-forward the known sustainable dissipatable power */
power_range = tz->tzp->sustainable_power + frac_to_int(power_range);
power_range = clamp(power_range, (s64)0, (s64)max_allocatable_power);
trace_thermal_power_allocator_pid(tz, frac_to_int(err),
frac_to_int(params->err_integral),
frac_to_int(p), frac_to_int(i),
frac_to_int(d), power_range);
return power_range;
}
/**
* divvy_up_power() - divvy the allocated power between the actors
* @req_power: each actor's requested power
* @max_power: each actor's maximum available power
* @num_actors: size of the @req_power, @max_power and @granted_power's array
* @total_req_power: sum of @req_power
* @power_range: total allocated power
* @granted_power: output array: each actor's granted power
* @extra_actor_power: an appropriately sized array to be used in the
* function as temporary storage of the extra power given
* to the actors
*
* This function divides the total allocated power (@power_range)
* fairly between the actors. It first tries to give each actor a
* share of the @power_range according to how much power it requested
* compared to the rest of the actors. For example, if only one actor
* requests power, then it receives all the @power_range. If
* three actors each requests 1mW, each receives a third of the
* @power_range.
*
* If any actor received more than their maximum power, then that
* surplus is re-divvied among the actors based on how far they are
* from their respective maximums.
*
* Granted power for each actor is written to @granted_power, which
* should've been allocated by the calling function.
*/
static void divvy_up_power(u32 *req_power, u32 *max_power, int num_actors,
u32 total_req_power, u32 power_range,
u32 *granted_power, u32 *extra_actor_power)
{
u32 extra_power, capped_extra_power;
int i;
/*
* Prevent division by 0 if none of the actors request power.
*/
if (!total_req_power)
total_req_power = 1;
capped_extra_power = 0;
extra_power = 0;
for (i = 0; i < num_actors; i++) {
u64 req_range = req_power[i] * power_range;
granted_power[i] = DIV_ROUND_CLOSEST_ULL(req_range,
total_req_power);
if (granted_power[i] > max_power[i]) {
extra_power += granted_power[i] - max_power[i];
granted_power[i] = max_power[i];
}
extra_actor_power[i] = max_power[i] - granted_power[i];
capped_extra_power += extra_actor_power[i];
}
if (!extra_power)
return;
/*
* Re-divvy the reclaimed extra among actors based on
* how far they are from the max
*/
extra_power = min(extra_power, capped_extra_power);
if (capped_extra_power > 0)
for (i = 0; i < num_actors; i++)
granted_power[i] += (extra_actor_power[i] *
extra_power) / capped_extra_power;
}
static int allocate_power(struct thermal_zone_device *tz,
unsigned long current_temp,
unsigned long control_temp)
{
struct thermal_instance *instance;
struct power_allocator_params *params = tz->governor_data;
u32 *req_power, *max_power, *granted_power, *extra_actor_power;
u32 *weighted_req_power;
u32 total_req_power, max_allocatable_power, total_weighted_req_power;
u32 total_granted_power, power_range;
int i, num_actors, total_weight, ret = 0;
int trip_max_desired_temperature = params->trip_max_desired_temperature;
mutex_lock(&tz->lock);
num_actors = 0;
total_weight = 0;
list_for_each_entry(instance, &tz->thermal_instances, tz_node) {
if ((instance->trip == trip_max_desired_temperature) &&
cdev_is_power_actor(instance->cdev)) {
num_actors++;
total_weight += instance->weight;
}
}
/*
* We need to allocate five arrays of the same size:
* req_power, max_power, granted_power, extra_actor_power and
* weighted_req_power. They are going to be needed until this
* function returns. Allocate them all in one go to simplify
* the allocation and deallocation logic.
*/
BUILD_BUG_ON(sizeof(*req_power) != sizeof(*max_power));
BUILD_BUG_ON(sizeof(*req_power) != sizeof(*granted_power));
BUILD_BUG_ON(sizeof(*req_power) != sizeof(*extra_actor_power));
BUILD_BUG_ON(sizeof(*req_power) != sizeof(*weighted_req_power));
req_power = devm_kcalloc(&tz->device, num_actors * 5,
sizeof(*req_power), GFP_KERNEL);
if (!req_power) {
ret = -ENOMEM;
goto unlock;
}
max_power = &req_power[num_actors];
granted_power = &req_power[2 * num_actors];
extra_actor_power = &req_power[3 * num_actors];
weighted_req_power = &req_power[4 * num_actors];
i =
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