5 files changed, 726 insertions, 1 deletions

diff --git a/drivers/cpuidle/Kconfig b/drivers/cpuidle/Kconfig
index 78a666d1e5f5..a76b689e553b 100644
--- a/drivers/cpuidle/Kconfig
+++ b/drivers/cpuidle/Kconfig
@@ -18,3 +18,6 @@ config CPU_IDLE_GOV_MENU
         bool
         depends on CPU_IDLE && NO_HZ
         default y
+
+config ARCH_NEEDS_CPU_IDLE_COUPLED
+        def_bool n
diff --git a/drivers/cpuidle/Makefile b/drivers/cpuidle/Makefile
index 5634f88379df..38c8f69f30cf 100644
--- a/drivers/cpuidle/Makefile
+++ b/drivers/cpuidle/Makefile
@@ -3,3 +3,4 @@
 #
 
 obj-y += cpuidle.o driver.o governor.o sysfs.o governors/
+obj-$(CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED) += coupled.o
diff --git a/drivers/cpuidle/coupled.c b/drivers/cpuidle/coupled.c
new file mode 100644
index 000000000000..aab6bba8daec
--- /dev/null
+++ b/drivers/cpuidle/coupled.c
@@ -0,0 +1,678 @@
+/*
+ * 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_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);
+        }
+
+        /* 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);
+        }
+
+        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;
+
+        mutex_lock(&cpuidle_lock);
+
+        dev = per_cpu(cpuidle_devices, cpu);
+        if (!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);
diff --git a/drivers/cpuidle/cpuidle.c b/drivers/cpuidle/cpuidle.c
index 4540672a2e1c..e81cfda295a5 100644
--- a/drivers/cpuidle/cpuidle.c
+++ b/drivers/cpuidle/cpuidle.c
@@ -171,7 +171,11 @@ int cpuidle_idle_call(void)
         trace_power_start_rcuidle(POWER_CSTATE, next_state, dev->cpu);
         trace_cpu_idle_rcuidle(next_state, dev->cpu);
 
-        entered_state = cpuidle_enter_state(dev, drv, next_state);
+        if (cpuidle_state_is_coupled(dev, drv, next_state))
+                entered_state = cpuidle_enter_state_coupled(dev, drv,
+                                                            next_state);
+        else
+                entered_state = cpuidle_enter_state(dev, drv, next_state);
 
         trace_power_end_rcuidle(dev->cpu);
         trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, dev->cpu);
@@ -407,9 +411,16 @@ static int __cpuidle_register_device(struct cpuidle_device *dev)
         if (ret)
                 goto err_sysfs;
 
+        ret = cpuidle_coupled_register_device(dev);
+        if (ret)
+                goto err_coupled;
+
         dev->registered = 1;
         return 0;
 
+err_coupled:
+        cpuidle_remove_sysfs(cpu_dev);
+        wait_for_completion(&dev->kobj_unregister);
 err_sysfs:
         list_del(&dev->device_list);
         per_cpu(cpuidle_devices, dev->cpu) = NULL;
@@ -464,6 +475,8 @@ void cpuidle_unregister_device(struct cpuidle_device *dev)
         wait_for_completion(&dev->kobj_unregister);
         per_cpu(cpuidle_devices, dev->cpu) = NULL;
 
+        cpuidle_coupled_unregister_device(dev);
+
         cpuidle_resume_and_unlock();
 
         module_put(cpuidle_driver->owner);
diff --git a/drivers/cpuidle/cpuidle.h b/drivers/cpuidle/cpuidle.h
index d8a3ccce8281..76e7f696ad8c 100644
--- a/drivers/cpuidle/cpuidle.h
+++ b/drivers/cpuidle/cpuidle.h
@@ -32,4 +32,34 @@ extern void cpuidle_remove_state_sysfs(struct cpuidle_device *device);
 extern int cpuidle_add_sysfs(struct device *dev);
 extern void cpuidle_remove_sysfs(struct device *dev);
 
+#ifdef CONFIG_ARCH_NEEDS_CPU_IDLE_COUPLED
+bool cpuidle_state_is_coupled(struct cpuidle_device *dev,
+                struct cpuidle_driver *drv, int state);
+int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
+                struct cpuidle_driver *drv, int next_state);
+int cpuidle_coupled_register_device(struct cpuidle_device *dev);
+void cpuidle_coupled_unregister_device(struct cpuidle_device *dev);
+#else
+static inline bool cpuidle_state_is_coupled(struct cpuidle_device *dev,
+                struct cpuidle_driver *drv, int state)
+{
+        return false;
+}
+
+static inline int cpuidle_enter_state_coupled(struct cpuidle_device *dev,
+                struct cpuidle_driver *drv, int next_state)
+{
+        return -1;
+}
+
+static inline int cpuidle_coupled_register_device(struct cpuidle_device *dev)
+{
+        return 0;
+}
+
+static inline void cpuidle_coupled_unregister_device(struct cpuidle_device *dev)
+{
+}
+#endif
+
 #endif /* __DRIVER_CPUIDLE_H */