/*
* coupled.c - helper functions to enter the same idle state on multiple cpus
*
* Copyright (c) 2011 Google, Inc.
*
* Author: Colin Cross <ccross@android.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; either version 2 of the License, or
* (at your option) any later version.
*
* 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/kernel.h>
#include <linux/cpu.h>
#include <linux/cpuidle.h>
#include <linux/mutex.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include "cpuidle.h"
/**
* DOC: Coupled cpuidle states
*
* On some ARM SMP SoCs (OMAP4460, Tegra 2, and probably more), the
* cpus cannot be independently powered down, either due to
* sequencing restrictions (on Tegra 2, cpu 0 must be the last to
* power down), or due to HW bugs (on OMAP4460, a cpu powering up
* will corrupt the gic state unless the other cpu runs a work
* around). Each cpu has a power state that it can enter without
* coordinating with the other cpu (usually Wait For Interrupt, or
* WFI), and one or more "coupled" power states that affect blocks
* shared between the cpus (L2 cache, interrupt controller, and
* sometimes the whole SoC). Entering a coupled power state must
* be tightly controlled on both cpus.
*
* This file implements a solution, where each cpu will wait in the
* WFI state until all cpus are ready to enter a coupled state, at
* which point the coupled state function will be called on all
* cpus at approximately the same time.
*
* Once all cpus are ready to enter idle, they are woken by an smp
* cross call. At this point, there is a chance that one of the
* cpus will find work to do, and choose not to enter idle. A
* final pass is needed to guarantee that all cpus will call the
* power state enter function at the same time. During this pass,
* each cpu will increment the ready counter, and continue once the
* ready counter matches the number of online coupled cpus. If any
* cpu exits idle, the other cpus will decrement their counter and
* retry.
*
* requested_state stores the deepest coupled idle state each cpu
* is ready for. It is assumed that the states are indexed from
* shallowest (highest power, lowest exit latency) to deepest
* (lowest power, highest exit latency). The requested_state
* variable is not locked. It is only written from the cpu that
* it stores (or by the on/offlining cpu if that cpu is offline),
* and only read after all the cpus are ready for the coupled idle
* state are are no longer updating it.
*
* Three atomic counters are used. alive_count tracks the number
* of cpus in the coupled set that are currently or soon will be
* online. waiting_count tracks the number of cpus that are in
* the waiting loop, in the ready loop, or in the coupled idle state.
* ready_count tracks the number of cpus that are in the ready loop
* or in the coupled idle state.
*
* To use coupled cpuidle states, a cpuidle driver must:
*
* Set struct cpuidle_device.coupled_cpus to the mask of all
* coupled cpus, usually the same as cpu_possible_mask if all cpus
* are part of the same cluster. The coupled_cpus mask must be
* set in the struct cpuidle_device for each cpu.
*
* Set struct cpuidle_device.safe_state to a state that is not a
* coupled state. This is usually WFI.
*
* Set CPUIDLE_FLAG_COUPLED in struct cpuidle_state.flags for each
* state that affects multiple cpus.
*
* Provide a struct cpuidle_state.enter function for each state
* that affects multiple cpus. This function is guaranteed to be
* called on all cpus at approximately the same time. The driver
* should ensure that the cpus all abort together if any cpu tries
* to abort once the function is called. The function should return
* with interrupts still disabled.
*/
/**
* struct cpuidle_coupled - data for set of cpus that share a coupled idle state
* @coupled_cpus: mask of cpus that are part of the coupled set
* @requested_state: array of requested states for cpus in the coupled set
* @ready_waiting_counts: combined count of cpus in ready or waiting loops
* @online_count: count of cpus that are online
* @refcnt: reference count of cpuidle devices that are using this struct
* @prevent: flag to prevent coupled idle while a cpu is hotplugging
*/
struct cpuidle_coupled {
cpumask_t coupled_cpus;
int requested_state[NR_CPUS];
atomic_t ready_waiting_counts;
int online_count;
int refcnt;
int prevent;
};
#define WAITING_BITS 16
#define MAX_WAITING_CPUS (1 << WAITING_BITS)
#define WAITING_MASK (MAX_WAITING_CPUS - 1)
#define READY_MASK (~WAITING_MASK)
#define CPUIDLE_COUPLED_NOT_IDLE (-1)
static DEFINE_MUTEX(cpuidle_coupled_lock);
static DEFINE_PER_CPU(struct call_single_data, cpuidle_coupled_poke_cb);
/*
* The cpuidle_coupled_poked_mask mask is used to avoid calling
* __smp_call_function_single with the per cpu call_single_data struct already
* in use. This prevents a deadlock where two cpus are waiting for each others
* call_single_data struct to be available
*/
static cpumask_t cpuidle_coupled_poked_mask;
/**
* cpuidle_coupled_parallel_barrier - synchronize all online coupled cpus
* @dev: cpuidle_device of the calling cpu
* @a: atomic variable to hold the barrier
*
* No caller to this function will return from this function until all online
* cpus in the same coupled group have called this function. Once any caller
* has returned from this function, the barrier is immediately available for
* reuse.
*
* The atomic variable a must be initialized to 0 before any cpu calls
* this function, will be reset to 0 before any cpu returns from this function.
*
* Must only be called from within a coupled idle state handler
* (state.enter when state.flags has CPUIDLE_FLAG_COUPLED set).
*
* Provides full smp barrier semantics before and after calling.
*/
void cpuidle_coupled_parallel_barrier(struct cpuidle_device *dev, atomic_t *a)
{
int n = dev->coupled->online_count;
smp_mb__before_atomic_inc();
atomic_inc(a);
while (atomic_read(a) < n)
cpu_relax();
if (atomic_inc_return(a) == n * 2) {
atomic_set(a, 0);
return;
}
while (atomic_read(a) > n)
cpu_relax();
}
/**
* cpuidle_state_is_coupled - check if a state is part of a coupled set
* @dev: struct cpuidle_device for the current cpu
* @drv: struct cpuidle_driver for the platform
* @state: index of the target state in drv->states
*
* Returns true if the target state is coupled with cpus besides this one
*/
bool cpuidle_state_is_coupled(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int state)
{
return drv->states[state].flags & CPUIDLE_FLAG_COUPLED;
}
/**
* cpuidle_coupled_set_ready - mark a cpu as ready
* @coupled: the struct coupled that contains the current cpu
*/
static inline void cpuidle_coupled_set_ready(struct cpuidle_coupled *coupled)
{
atomic_add(MAX_WAITING_CPUS, &coupled->ready_waiting_counts);
}
/**
* cpuidle_coupled_set_not_ready - mark a cpu as not ready
* @coupled: the struct coupled that contains the current cpu
*
* Decrements the ready counter, unless the ready (and thus the waiting) counter
* is equal to the number of online cpus. Prevents a race where one cpu
* decrements the waiting counter and then re-increments it just before another
* cpu has decremented its ready counter, leading to the ready counter going
* down from the number of online cpus without going through the coupled idle
* state.
*
* Returns 0 if the counter was decremented successfully, -EINVAL if the ready
* counter was equal to the number of online cpus.
*/
static
inline int cpuidle_coupled_set_not_ready(struct cpuidle_coupled *coupled)
{
int all;
int ret;
all = coupled->online_count | (coupled->online_count << WAITING_BITS);
ret = atomic_add_unless(&coupled->ready_waiting_counts,
-MAX_WAITING_CPUS, all);
return ret ? 0 : -EINVAL;
}
/**
* cpuidle_coupled_no_cpus_ready - check if no cpus in a coupled set are ready
* @coupled: the struct coupled that contains the current cpu
*
* Returns true if all of the cpus in a coupled set are out of the ready loop.
*/
static inline int cpuidle_coupled_no_cpus_ready(struct cpuidle_coupled *coupled)
{
int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS;
return r == 0;
}
/**
* cpuidle_coupled_cpus_ready - check if all cpus in a coupled set are ready
* @coupled: the struct coupled that contains the current cpu
*
* Returns true if all cpus coupled to this target state are in the ready loop
*/
static inline bool cpuidle_coupled_cpus_ready(struct cpuidle_coupled *coupled)
{
int r = atomic_read(&coupled->ready_waiting_counts) >> WAITING_BITS;
return r == coupled->online_count;
}
/**
* cpuidle_coupled_cpus_waiting - check if all cpus in a coupled set are waiting
* @coupled: the struct coupled that contains the current cpu
*
* Returns true if all cpus coupled to this target state are in the wait loop
*/
static inline bool cpuidle_coupled_cpus_waiting(struct cpuidle_coupled *coupled)
{
int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK;
return w == coupled->online_count;
}
/**
* cpuidle_coupled_no_cpus_waiting - check if no cpus in coupled set are waiting
* @coupled: the struct coupled that contains the current cpu
*
* Returns true if all of the cpus in a coupled set are out of the waiting loop.
*/
static inline int cpuidle_coupled_no_cpus_waiting(struct cpuidle_coupled *coupled)
{
int w = atomic_read(&coupled->ready_waiting_counts) & WAITING_MASK;
return w == 0;
}
/**
* cpuidle_coupled_get_state - determine the deepest idle state
* @dev: struct cpuidle_device for this cpu
* @coupled: the struct coupled that contains the current cpu
*
* Returns the deepest idle state that all coupled cpus can enter
*/
static inline int cpuidle_coupled_get_state(struct cpuidle_device *dev,
struct cpuidle_coupled *coupled)
{
int i;
int state = INT_MAX;
/*
* Read barrier ensures that read of requested_state is ordered after
* reads of ready_count. Matches the write barriers
* cpuidle_set_state_waiting.
*/
smp_rmb();
for_each_cpu_mask(i, coupled->coupled_cpus)
if (cpu_online(i) && coupled->requested_state[i] < state)
state = coupled->requested_state[i];
return state;
}
static void cpuidle_coupled_poked(void *info)
{
int cpu = (unsigned long)info;
cpumask_clear_cpu(cpu, &cpuidle_coupled_poked_mask);
}
/**
* cpuidle_coupled_poke - wake up a cpu that may be waiting
* @cpu: target cpu
*
* Ensures that the target cpu exits it's waiting idle state (if it is in it)
* and will see updates to waiting_count before it re-enters it's waiting idle
* state.
*
* If cpuidle_coupled_poked_mask is already set for the target cpu, that cpu
* either has or will soon have a pending IPI that will wake it out of idle,
* or it is currently processing the IPI and is not in idle.
*/
static void cpuidle_coupled_poke(int cpu)
{
struct call_single_data *csd = &per_cpu(cpuidle_coupled_poke_cb, cpu);
if (!cpumask_test_and_set_cpu(cpu, &cpuidle_coupled_poked_mask))
__smp_call_function_single(cpu, csd, 0);
}
/**
* cpuidle_coupled_poke_others - wake up all other cpus that may be waiting
* @dev: struct cpuidle_device for this cpu
* @coupled: the struct coupled that contains the current cpu
*
* Calls cpuidle_coupled_poke on all other online cpus.
*/
static void cpuidle_coupled_poke_others(int this_cpu,
struct cpuidle_coupled *coupled)
{
int cpu;
for_each_cpu_mask(cpu, coupled->coupled_cpus)
if (cpu != this_cpu && cpu_online(cpu))
cpuidle_coupled_poke(cpu);
}
/**
* cpuidle_coupled_set_waiting - mark this cpu as in the wait loop
* @dev: struct cpuidle_device for this cpu
* @coupled: the struct coupled that contains the current cpu
* @next_state: the index in drv->states of the requested state for this cpu
*
* Updates the requested idle state for the specified cpuidle device,
* poking all coupled cpus out of idle if necessary to let them see the new
* state.
*/
static void cpuidle_coupled_set_waiting(int cpu,
struct cpuidle_coupled *coupled, int next_state)
{
int w;
coupled->requested_state[cpu] = next_state;
/*
* If this is the last cpu to enter the waiting state, poke
* all the other cpus out of their waiting state so they can
* enter a deeper state. This can race with one of the cpus
* exiting the waiting state due to an interrupt and
* decrementing waiting_count, see comment below.
*
* The atomic_inc_return provides a write barrier to order the write
* to requested_state with the later write that increments ready_count.
*/
w = atomic_inc_return(&coupled->ready_waiting_counts) & WAITING_MASK;
if (w == coupled->online_count)
cpuidle_coupled_poke_others(cpu, coupled);
}
/**
* cpuidle_coupled_set_not_waiting - mark this cpu as leaving the wait loop
* @dev: struct cpuidle_device for this cpu
* @coupled: the struct coupled that contains the current cpu
*
* Removes the requested idle state for the specified cpuidle device.
*/
static void cpuidle_coupled_set_not_waiting(int cpu,
struct cpuidle_coupled *coupled)
{
/*
* Decrementing waiting count can race with incrementing it in
* cpuidle_coupled_set_waiting, but that's OK. Worst case, some
* cpus will increment ready_count and then spin until they
* notice that this cpu has cleared it's requested_state.
*/
atomic_dec(&coupled->ready_waiting_counts);
coupled->requested_state[cpu] = CPUIDLE_COUPLED_NOT_IDLE;
}
/**
* cpuidle_coupled_set_done - mark this cpu as leaving the ready loop
* @cpu: the current cpu
* @coupled: the struct coupled that contains the current cpu
*
* Marks this cpu as no longer in the ready and waiting loops. Decrements
* the waiting count first to prevent another cpu looping back in and seeing
* this cpu as waiting just before it exits idle.
*/
static void cpuidle_coupled_set_done(int cpu, struct cpuidle_coupled *coupled)
{
cpuidle_coupled_set_not_waiting(cpu, coupled);
atomic_sub(MAX_WAITING_CPUS, &coupled->ready_waiting_counts);
}
/**
* cpuidle_coupled_clear_pokes - spin until the poke interrupt is processed
* @cpu - this cpu
*
* Turns on interrupts and spins until any outstanding poke interrupts have
* been processed and the poke bit has been cleared.
*
* Other interrupts may also be processed while interrupts are enabled, so
* need_resched() must be tested after turning interrupts off again to make sure
* the interrupt didn't schedule work that should take the cpu out of idle.
*
* Returns 0 if need_resched was false, -EINTR if need_resched was true.
*/
static int cpuidle_coupled_clear_pokes(int cpu)
{
local_irq_enable();
while (cpumask_test_cpu(cpu, &cpuidle_coupled_poked_mask))
cpu_relax();
local_irq_disable();
return need_resched() ? -EINTR : 0;
}
/**
* cpuidle_enter_state_coupled - attempt to enter a state with coupled cpus
* @dev: struct cpuidle_device for the current cpu
* @drv: struct cpuidle_driver for the platform
* @next_state: index of the requested state in drv->states
*
* Coordinate with coupled cpus to enter the target state. This is a two
* stage process. In the first stage, the cpus are operating independently,
* and may call into cpuidle_enter_state_coupled at completely different times.
* To save as much power as possible, the first cpus to call this function will
* go to an intermediate state (the cpuidle_device's safe state), and wait for
* all the other cpus to call this function. Once all coupled cpus are idle,
* the second stage will start. Each coupled cpu will spin until all cpus have
* guaranteed that they will call the target_state.
*
* This function must be called with interrupts disabled. It may enable
* interrupts while preparing for idle, and it will always return with
* interrupts enabled.
*/
int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int next_state)
{
int entered_state = -1;
struct cpuidle_coupled *coupled = dev->coupled;
if (!coupled)
return -EINVAL;
while (coupled->prevent) {
if (cpuidle_coupled_clear_pokes(dev->cpu)) {
local_irq_enable();
return entered_state;
}
entered_state = cpuidle_enter_state(dev, drv,
dev->safe_state_index);
local_irq_disable();
}
/* Read barrier ensures online_count is read after prevent is cleared */
smp_rmb();
cpuidle_coupled_set_waiting(dev->cpu, coupled, next_state);
retry:
/*
* Wait for all coupled cpus to be idle, using the deepest state
* allowed for a single cpu.
*/
while (!cpuidle_coupled_cpus_waiting(coupled)) {
if (cpuidle_coupled_clear_pokes(dev->cpu)) {
cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
goto out;
}
if (coupled->prevent) {
cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
goto out;
}
entered_state = cpuidle_enter_state(dev, drv,
dev->safe_state_index);
local_irq_disable();
}
if (cpuidle_coupled_clear_pokes(dev->cpu)) {
cpuidle_coupled_set_not_waiting(dev->cpu, coupled);
goto out;
}
/*
* All coupled cpus are probably idle. There is a small chance that
* one of the other cpus just became active. Increment the ready count,
* and spin until all coupled cpus have incremented the counter. Once a
* cpu has incremented the ready counter, it cannot abort idle and must
* spin until either all cpus have incremented the ready counter, or
* another cpu leaves idle and decrements the waiting counter.
*/
cpuidle_coupled_set_ready(coupled);
while (!cpuidle_coupled_cpus_ready(coupled)) {
/* Check if any other cpus bailed out of idle. */
if (!cpuidle_coupled_cpus_waiting(coupled))
if (!cpuidle_coupled_set_not_ready(coupled))
goto retry;
cpu_relax();
}
/* all cpus have acked the coupled state */
next_state = cpuidle_coupled_get_state(dev, coupled);
entered_state = cpuidle_enter_state(dev, drv, next_state);
cpuidle_coupled_set_done(dev->cpu, coupled);
out:
/*
* Normal cpuidle states are expected to return with irqs enabled.
* That leads to an inefficiency where a cpu receiving an interrupt
* that brings it out of idle will process that interrupt before
* exiting the idle enter function and decrementing ready_count. All
* other cpus will need to spin waiting for the cpu that is processing
* the interrupt. If the driver returns with interrupts disabled,
* all other cpus will loop back into the safe idle state instead of
* spinning, saving power.
*
* Calling local_irq_enable here allows coupled states to return with
* interrupts disabled, but won't cause problems for drivers that
* exit with interrupts enabled.
*/
local_irq_enable();
/*
* Wait until all coupled cpus have exited idle. There is no risk that
* a cpu exits and re-enters the ready state because this cpu has
* already decremented its waiting_count.
*/
while (!cpuidle_coupled_no_cpus_ready(coupled))
cpu_relax();
return entered_state;
}
static void cpuidle_coupled_update_online_cpus(struct cpuidle_coupled *coupled)
{
cpumask_t cpus;
cpumask_and(&cpus, cpu_online_mask, &coupled->coupled_cpus);
coupled->online_count = cpumask_weight(&cpus);
}
/**
* cpuidle_coupled_register_device - register a coupled cpuidle device
* @dev: struct cpuidle_device for the current cpu
*
* Called from cpuidle_register_device to handle coupled idle init. Finds the
* cpuidle_coupled struct for this set of coupled cpus, or creates one if none
* exists yet.
*/
int cpuidle_coupled_register_device(struct cpuidle_device *dev)
{
int cpu;
struct cpuidle_device *other_dev;
struct call_single_data *csd;
struct cpuidle_coupled *coupled;
if (cpumask_empty(&dev->coupled_cpus))
return 0;
for_each_cpu_mask(cpu, dev->coupled_cpus) {
other_dev = per_cpu(cpuidle_devices, cpu);
if (other_dev && other_dev->coupled) {
coupled = other_dev->coupled;
goto have_coupled;
}
}
/* No existing coupled info found, create a new one */
coupled = kzalloc(sizeof(struct cpuidle_coupled), GFP_KERNEL);
if (!coupled)
return -ENOMEM;
coupled->coupled_cpus = dev->coupled_cpus;
have_coupled:
dev->coupled = coupled;
if (WARN_ON(!cpumask_equal(&dev->coupled_cpus, &coupled->coupled_cpus)))
coupled->prevent++;
cpuidle_coupled_update_online_cpus(coupled);
coupled->refcnt++;
csd = &per_cpu(cpuidle_coupled_poke_cb, dev->cpu);
csd->func = cpuidle_coupled_poked;
csd->info = (void *)(unsigned long)dev->cpu;
return 0;
}
/**
* cpuidle_coupled_unregister_device - unregister a coupled cpuidle device
* @dev: struct cpuidle_device for the current cpu
*
* Called from cpuidle_unregister_device to tear down coupled idle. Removes the
* cpu from the coupled idle set, and frees the cpuidle_coupled_info struct if
* this was the last cpu in the set.
*/
void cpuidle_coupled_unregister_device(struct cpuidle_device *dev)
{
struct cpuidle_coupled *coupled = dev->coupled;
if (cpumask_empty(&dev->coupled_cpus))
return;
if (--coupled->refcnt)
kfree(coupled);
dev->coupled = NULL;
}
/**
* cpuidle_coupled_prevent_idle - prevent cpus from entering a coupled state
* @coupled: the struct coupled that contains the cpu that is changing state
*
* Disables coupled cpuidle on a coupled set of cpus. Used to ensure that
* cpu_online_mask doesn't change while cpus are coordinating coupled idle.
*/
static void cpuidle_coupled_prevent_idle(struct cpuidle_coupled *coupled)
{
int cpu = get_cpu();
/* Force all cpus out of the waiting loop. */
coupled->prevent++;
cpuidle_coupled_poke_others(cpu, coupled);
put_cpu();
while (!cpuidle_coupled_no_cpus_waiting(coupled))
cpu_relax();
}
/**
* cpuidle_coupled_allow_idle - allows cpus to enter a coupled state
* @coupled: the struct coupled that contains the cpu that is changing state
*
* Enables coupled cpuidle on a coupled set of cpus. Used to ensure that
* cpu_online_mask doesn't change while cpus are coordinating coupled idle.
*/
static void cpuidle_coupled_allow_idle(struct cpuidle_coupled *coupled)
{
int cpu = get_cpu();
/*
* Write barrier ensures readers see the new online_count when they
* see prevent == 0.
*/
smp_wmb();
coupled->prevent--;
/* Force cpus out of the prevent loop. */
cpuidle_coupled_poke_others(cpu, coupled);
put_cpu();
}
/**
* cpuidle_coupled_cpu_notify - notifier called during hotplug transitions
* @nb: notifier block
* @action: hotplug transition
* @hcpu: target cpu number
*
* Called when a cpu is brought on or offline using hotplug. Updates the
* coupled cpu set appropriately
*/
static int cpuidle_coupled_cpu_notify(struct notifier_block *nb,
unsigned long action, void *hcpu)
{
int cpu = (unsigned long)hcpu;
struct cpuidle_device *dev;
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_UP_PREPARE:
case CPU_DOWN_PREPARE:
case CPU_ONLINE:
case CPU_DEAD:
case CPU_UP_CANCELED:
case CPU_DOWN_FAILED:
break;
default:
return NOTIFY_OK;
}
mutex_lock(&cpuidle_lock);
dev = per_cpu(cpuidle_devices, cpu);
if (!dev || !dev->coupled)
goto out;
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_UP_PREPARE:
case CPU_DOWN_PREPARE:
cpuidle_coupled_prevent_idle(dev->coupled);
break;
case CPU_ONLINE:
case CPU_DEAD:
cpuidle_coupled_update_online_cpus(dev->coupled);
/* Fall through */
case CPU_UP_CANCELED:
case CPU_DOWN_FAILED:
cpuidle_coupled_allow_idle(dev->coupled);
break;
}
out:
mutex_unlock(&cpuidle_lock);
return NOTIFY_OK;
}
static struct notifier_block cpuidle_coupled_cpu_notifier = {
.notifier_call = cpuidle_coupled_cpu_notify,
};
static int __init cpuidle_coupled_init(void)
{
return register_cpu_notifier(&cpuidle_coupled_cpu_notifier);
}
core_initcall(cpuidle_coupled_init);
