mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race

[linux/fpc-iii.git] / arch / arm / common / bL_switcher.c

/*
 * arch/arm/common/bL_switcher.c -- big.LITTLE cluster switcher core driver
 *
 * Created by:  Nicolas Pitre, March 2012
 * Copyright:   (C) 2012-2013  Linaro Limited
 *
 * 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.
 */

#include <linux/atomic.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched/signal.h>
#include <uapi/linux/sched/types.h>
#include <linux/interrupt.h>
#include <linux/cpu_pm.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/kthread.h>
#include <linux/wait.h>
#include <linux/time.h>
#include <linux/clockchips.h>
#include <linux/hrtimer.h>
#include <linux/tick.h>
#include <linux/notifier.h>
#include <linux/mm.h>
#include <linux/mutex.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <linux/string.h>
#include <linux/sysfs.h>
#include <linux/irqchip/arm-gic.h>
#include <linux/moduleparam.h>

#include <asm/smp_plat.h>
#include <asm/cputype.h>
#include <asm/suspend.h>
#include <asm/mcpm.h>
#include <asm/bL_switcher.h>

#define CREATE_TRACE_POINTS
#include <trace/events/power_cpu_migrate.h>


/*
 * Use our own MPIDR accessors as the generic ones in asm/cputype.h have
 * __attribute_const__ and we don't want the compiler to assume any
 * constness here as the value _does_ change along some code paths.
 */

static int read_mpidr(void)
{
        unsigned int id;
        asm volatile ("mrc p15, 0, %0, c0, c0, 5" : "=r" (id));
        return id & MPIDR_HWID_BITMASK;
}

/*
 * bL switcher core code.
 */

static void bL_do_switch(void *_arg)
{
        unsigned ib_mpidr, ib_cpu, ib_cluster;
        long volatile handshake, **handshake_ptr = _arg;

        pr_debug("%s\n", __func__);

        ib_mpidr = cpu_logical_map(smp_processor_id());
        ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
        ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);

        /* Advertise our handshake location */
        if (handshake_ptr) {
                handshake = 0;
                *handshake_ptr = &handshake;
        } else
                handshake = -1;

        /*
         * Our state has been saved at this point.  Let's release our
         * inbound CPU.
         */
        mcpm_set_entry_vector(ib_cpu, ib_cluster, cpu_resume);
        sev();

        /*
         * From this point, we must assume that our counterpart CPU might
         * have taken over in its parallel world already, as if execution
         * just returned from cpu_suspend().  It is therefore important to
         * be very careful not to make any change the other guy is not
         * expecting.  This is why we need stack isolation.
         *
         * Fancy under cover tasks could be performed here.  For now
         * we have none.
         */

        /*
         * Let's wait until our inbound is alive.
         */
        while (!handshake) {
                wfe();
                smp_mb();
        }

        /* Let's put ourself down. */
        mcpm_cpu_power_down();

        /* should never get here */
        BUG();
}

/*
 * Stack isolation.  To ensure 'current' remains valid, we just use another
 * piece of our thread's stack space which should be fairly lightly used.
 * The selected area starts just above the thread_info structure located
 * at the very bottom of the stack, aligned to a cache line, and indexed
 * with the cluster number.
 */
#define STACK_SIZE 512
extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
static int bL_switchpoint(unsigned long _arg)
{
        unsigned int mpidr = read_mpidr();
        unsigned int clusterid = MPIDR_AFFINITY_LEVEL(mpidr, 1);
        void *stack = current_thread_info() + 1;
        stack = PTR_ALIGN(stack, L1_CACHE_BYTES);
        stack += clusterid * STACK_SIZE + STACK_SIZE;
        call_with_stack(bL_do_switch, (void *)_arg, stack);
        BUG();
}

/*
 * Generic switcher interface
 */

static unsigned int bL_gic_id[MAX_CPUS_PER_CLUSTER][MAX_NR_CLUSTERS];
static int bL_switcher_cpu_pairing[NR_CPUS];

/*
 * bL_switch_to - Switch to a specific cluster for the current CPU
 * @new_cluster_id: the ID of the cluster to switch to.
 *
 * This function must be called on the CPU to be switched.
 * Returns 0 on success, else a negative status code.
 */
static int bL_switch_to(unsigned int new_cluster_id)
{
        unsigned int mpidr, this_cpu, that_cpu;
        unsigned int ob_mpidr, ob_cpu, ob_cluster, ib_mpidr, ib_cpu, ib_cluster;
        struct completion inbound_alive;
        long volatile *handshake_ptr;
        int ipi_nr, ret;

        this_cpu = smp_processor_id();
        ob_mpidr = read_mpidr();
        ob_cpu = MPIDR_AFFINITY_LEVEL(ob_mpidr, 0);
        ob_cluster = MPIDR_AFFINITY_LEVEL(ob_mpidr, 1);
        BUG_ON(cpu_logical_map(this_cpu) != ob_mpidr);

        if (new_cluster_id == ob_cluster)
                return 0;

        that_cpu = bL_switcher_cpu_pairing[this_cpu];
        ib_mpidr = cpu_logical_map(that_cpu);
        ib_cpu = MPIDR_AFFINITY_LEVEL(ib_mpidr, 0);
        ib_cluster = MPIDR_AFFINITY_LEVEL(ib_mpidr, 1);

        pr_debug("before switch: CPU %d MPIDR %#x -> %#x\n",
                 this_cpu, ob_mpidr, ib_mpidr);

        this_cpu = smp_processor_id();

        /* Close the gate for our entry vectors */
        mcpm_set_entry_vector(ob_cpu, ob_cluster, NULL);
        mcpm_set_entry_vector(ib_cpu, ib_cluster, NULL);

        /* Install our "inbound alive" notifier. */
        init_completion(&inbound_alive);
        ipi_nr = register_ipi_completion(&inbound_alive, this_cpu);
        ipi_nr |= ((1 << 16) << bL_gic_id[ob_cpu][ob_cluster]);
        mcpm_set_early_poke(ib_cpu, ib_cluster, gic_get_sgir_physaddr(), ipi_nr);

        /*
         * Let's wake up the inbound CPU now in case it requires some delay
         * to come online, but leave it gated in our entry vector code.
         */
        ret = mcpm_cpu_power_up(ib_cpu, ib_cluster);
        if (ret) {
                pr_err("%s: mcpm_cpu_power_up() returned %d\n", __func__, ret);
                return ret;
        }

        /*
         * Raise a SGI on the inbound CPU to make sure it doesn't stall
         * in a possible WFI, such as in bL_power_down().
         */
        gic_send_sgi(bL_gic_id[ib_cpu][ib_cluster], 0);

        /*
         * Wait for the inbound to come up.  This allows for other
         * tasks to be scheduled in the mean time.
         */
        wait_for_completion(&inbound_alive);
        mcpm_set_early_poke(ib_cpu, ib_cluster, 0, 0);

        /*
         * From this point we are entering the switch critical zone
         * and can't take any interrupts anymore.
         */
        local_irq_disable();
        local_fiq_disable();
        trace_cpu_migrate_begin(ktime_get_real_ns(), ob_mpidr);

        /* redirect GIC's SGIs to our counterpart */
        gic_migrate_target(bL_gic_id[ib_cpu][ib_cluster]);

        tick_suspend_local();

        ret = cpu_pm_enter();

        /* we can not tolerate errors at this point */
        if (ret)
                panic("%s: cpu_pm_enter() returned %d\n", __func__, ret);

        /* Swap the physical CPUs in the logical map for this logical CPU. */
        cpu_logical_map(this_cpu) = ib_mpidr;
        cpu_logical_map(that_cpu) = ob_mpidr;

        /* Let's do the actual CPU switch. */
        ret = cpu_suspend((unsigned long)&handshake_ptr, bL_switchpoint);
        if (ret > 0)
                panic("%s: cpu_suspend() returned %d\n", __func__, ret);

        /* We are executing on the inbound CPU at this point */
        mpidr = read_mpidr();
        pr_debug("after switch: CPU %d MPIDR %#x\n", this_cpu, mpidr);
        BUG_ON(mpidr != ib_mpidr);

        mcpm_cpu_powered_up();

        ret = cpu_pm_exit();

        tick_resume_local();

        trace_cpu_migrate_finish(ktime_get_real_ns(), ib_mpidr);
        local_fiq_enable();
        local_irq_enable();

        *handshake_ptr = 1;
        dsb_sev();

        if (ret)
                pr_err("%s exiting with error %d\n", __func__, ret);
        return ret;
}

struct bL_thread {
        spinlock_t lock;
        struct task_struct *task;
        wait_queue_head_t wq;
        int wanted_cluster;
        struct completion started;
        bL_switch_completion_handler completer;
        void *completer_cookie;
};

static struct bL_thread bL_threads[NR_CPUS];

static int bL_switcher_thread(void *arg)
{
        struct bL_thread *t = arg;
        struct sched_param param = { .sched_priority = 1 };
        int cluster;
        bL_switch_completion_handler completer;
        void *completer_cookie;

        sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
        complete(&t->started);

        do {
                if (signal_pending(current))
                        flush_signals(current);
                wait_event_interruptible(t->wq,
                                t->wanted_cluster != -1 ||
                                kthread_should_stop());

                spin_lock(&t->lock);
                cluster = t->wanted_cluster;
                completer = t->completer;
                completer_cookie = t->completer_cookie;
                t->wanted_cluster = -1;
                t->completer = NULL;
                spin_unlock(&t->lock);

                if (cluster != -1) {
                        bL_switch_to(cluster);

                        if (completer)
                                completer(completer_cookie);
                }
        } while (!kthread_should_stop());

        return 0;
}

static struct task_struct *bL_switcher_thread_create(int cpu, void *arg)
{
        struct task_struct *task;

        task = kthread_create_on_node(bL_switcher_thread, arg,
                                      cpu_to_node(cpu), "kswitcher_%d", cpu);
        if (!IS_ERR(task)) {
                kthread_bind(task, cpu);
                wake_up_process(task);
        } else
                pr_err("%s failed for CPU %d\n", __func__, cpu);
        return task;
}

/*
 * bL_switch_request_cb - Switch to a specific cluster for the given CPU,
 *      with completion notification via a callback
 *
 * @cpu: the CPU to switch
 * @new_cluster_id: the ID of the cluster to switch to.
 * @completer: switch completion callback.  if non-NULL,
 *      @completer(@completer_cookie) will be called on completion of
 *      the switch, in non-atomic context.
 * @completer_cookie: opaque context argument for @completer.
 *
 * This function causes a cluster switch on the given CPU by waking up
 * the appropriate switcher thread.  This function may or may not return
 * before the switch has occurred.
 *
 * If a @completer callback function is supplied, it will be called when
 * the switch is complete.  This can be used to determine asynchronously
 * when the switch is complete, regardless of when bL_switch_request()
 * returns.  When @completer is supplied, no new switch request is permitted
 * for the affected CPU until after the switch is complete, and @completer
 * has returned.
 */
int bL_switch_request_cb(unsigned int cpu, unsigned int new_cluster_id,
                         bL_switch_completion_handler completer,
                         void *completer_cookie)
{
        struct bL_thread *t;

        if (cpu >= ARRAY_SIZE(bL_threads)) {
                pr_err("%s: cpu %d out of bounds\n", __func__, cpu);
                return -EINVAL;
        }

        t = &bL_threads[cpu];

        if (IS_ERR(t->task))
                return PTR_ERR(t->task);
        if (!t->task)
                return -ESRCH;

        spin_lock(&t->lock);
        if (t->completer) {
                spin_unlock(&t->lock);
                return -EBUSY;
        }
        t->completer = completer;
        t->completer_cookie = completer_cookie;
        t->wanted_cluster = new_cluster_id;
        spin_unlock(&t->lock);
        wake_up(&t->wq);
        return 0;
}
EXPORT_SYMBOL_GPL(bL_switch_request_cb);

/*
 * Activation and configuration code.
 */

static DEFINE_MUTEX(bL_switcher_activation_lock);
static BLOCKING_NOTIFIER_HEAD(bL_activation_notifier);
static unsigned int bL_switcher_active;
static unsigned int bL_switcher_cpu_original_cluster[NR_CPUS];
static cpumask_t bL_switcher_removed_logical_cpus;

int bL_switcher_register_notifier(struct notifier_block *nb)
{
        return blocking_notifier_chain_register(&bL_activation_notifier, nb);
}
EXPORT_SYMBOL_GPL(bL_switcher_register_notifier);

int bL_switcher_unregister_notifier(struct notifier_block *nb)
{
        return blocking_notifier_chain_unregister(&bL_activation_notifier, nb);
}
EXPORT_SYMBOL_GPL(bL_switcher_unregister_notifier);

static int bL_activation_notify(unsigned long val)
{
        int ret;

        ret = blocking_notifier_call_chain(&bL_activation_notifier, val, NULL);
        if (ret & NOTIFY_STOP_MASK)
                pr_err("%s: notifier chain failed with status 0x%x\n",
                        __func__, ret);
        return notifier_to_errno(ret);
}

static void bL_switcher_restore_cpus(void)
{
        int i;

        for_each_cpu(i, &bL_switcher_removed_logical_cpus) {
                struct device *cpu_dev = get_cpu_device(i);
                int ret = device_online(cpu_dev);
                if (ret)
                        dev_err(cpu_dev, "switcher: unable to restore CPU\n");
        }
}

static int bL_switcher_halve_cpus(void)
{
        int i, j, cluster_0, gic_id, ret;
        unsigned int cpu, cluster, mask;
        cpumask_t available_cpus;

        /* First pass to validate what we have */
        mask = 0;
        for_each_online_cpu(i) {
                cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
                cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
                if (cluster >= 2) {
                        pr_err("%s: only dual cluster systems are supported\n", __func__);
                        return -EINVAL;
                }
                if (WARN_ON(cpu >= MAX_CPUS_PER_CLUSTER))
                        return -EINVAL;
                mask |= (1 << cluster);
        }
        if (mask != 3) {
                pr_err("%s: no CPU pairing possible\n", __func__);
                return -EINVAL;
        }

        /*
         * Now let's do the pairing.  We match each CPU with another CPU
         * from a different cluster.  To get a uniform scheduling behavior
         * without fiddling with CPU topology and compute capacity data,
         * we'll use logical CPUs initially belonging to the same cluster.
         */
        memset(bL_switcher_cpu_pairing, -1, sizeof(bL_switcher_cpu_pairing));
        cpumask_copy(&available_cpus, cpu_online_mask);
        cluster_0 = -1;
        for_each_cpu(i, &available_cpus) {
                int match = -1;
                cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);
                if (cluster_0 == -1)
                        cluster_0 = cluster;
                if (cluster != cluster_0)
                        continue;
                cpumask_clear_cpu(i, &available_cpus);
                for_each_cpu(j, &available_cpus) {
                        cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(j), 1);
                        /*
                         * Let's remember the last match to create "odd"
                         * pairings on purpose in order for other code not
                         * to assume any relation between physical and
                         * logical CPU numbers.
                         */
                        if (cluster != cluster_0)
                                match = j;
                }
                if (match != -1) {
                        bL_switcher_cpu_pairing[i] = match;
                        cpumask_clear_cpu(match, &available_cpus);
                        pr_info("CPU%d paired with CPU%d\n", i, match);
                }
        }

        /*
         * Now we disable the unwanted CPUs i.e. everything that has no
         * pairing information (that includes the pairing counterparts).
         */
        cpumask_clear(&bL_switcher_removed_logical_cpus);
        for_each_online_cpu(i) {
                cpu = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 0);
                cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(i), 1);

                /* Let's take note of the GIC ID for this CPU */
                gic_id = gic_get_cpu_id(i);
                if (gic_id < 0) {
                        pr_err("%s: bad GIC ID for CPU %d\n", __func__, i);
                        bL_switcher_restore_cpus();
                        return -EINVAL;
                }
                bL_gic_id[cpu][cluster] = gic_id;
                pr_info("GIC ID for CPU %u cluster %u is %u\n",
                        cpu, cluster, gic_id);

                if (bL_switcher_cpu_pairing[i] != -1) {
                        bL_switcher_cpu_original_cluster[i] = cluster;
                        continue;
                }

                ret = device_offline(get_cpu_device(i));
                if (ret) {
                        bL_switcher_restore_cpus();
                        return ret;
                }
                cpumask_set_cpu(i, &bL_switcher_removed_logical_cpus);
        }

        return 0;
}

/* Determine the logical CPU a given physical CPU is grouped on. */
int bL_switcher_get_logical_index(u32 mpidr)
{
        int cpu;

        if (!bL_switcher_active)
                return -EUNATCH;

        mpidr &= MPIDR_HWID_BITMASK;
        for_each_online_cpu(cpu) {
                int pairing = bL_switcher_cpu_pairing[cpu];
                if (pairing == -1)
                        continue;
                if ((mpidr == cpu_logical_map(cpu)) ||
                    (mpidr == cpu_logical_map(pairing)))
                        return cpu;
        }
        return -EINVAL;
}

static void bL_switcher_trace_trigger_cpu(void *__always_unused info)
{
        trace_cpu_migrate_current(ktime_get_real_ns(), read_mpidr());
}

int bL_switcher_trace_trigger(void)
{
        int ret;

        preempt_disable();

        bL_switcher_trace_trigger_cpu(NULL);
        ret = smp_call_function(bL_switcher_trace_trigger_cpu, NULL, true);

        preempt_enable();

        return ret;
}
EXPORT_SYMBOL_GPL(bL_switcher_trace_trigger);

static int bL_switcher_enable(void)
{
        int cpu, ret;

        mutex_lock(&bL_switcher_activation_lock);
        lock_device_hotplug();
        if (bL_switcher_active) {
                unlock_device_hotplug();
                mutex_unlock(&bL_switcher_activation_lock);
                return 0;
        }

        pr_info("big.LITTLE switcher initializing\n");

        ret = bL_activation_notify(BL_NOTIFY_PRE_ENABLE);
        if (ret)
                goto error;

        ret = bL_switcher_halve_cpus();
        if (ret)
                goto error;

        bL_switcher_trace_trigger();

        for_each_online_cpu(cpu) {
                struct bL_thread *t = &bL_threads[cpu];
                spin_lock_init(&t->lock);
                init_waitqueue_head(&t->wq);
                init_completion(&t->started);
                t->wanted_cluster = -1;
                t->task = bL_switcher_thread_create(cpu, t);
        }

        bL_switcher_active = 1;
        bL_activation_notify(BL_NOTIFY_POST_ENABLE);
        pr_info("big.LITTLE switcher initialized\n");
        goto out;

error:
        pr_warn("big.LITTLE switcher initialization failed\n");
        bL_activation_notify(BL_NOTIFY_POST_DISABLE);

out:
        unlock_device_hotplug();
        mutex_unlock(&bL_switcher_activation_lock);
        return ret;
}

#ifdef CONFIG_SYSFS

static void bL_switcher_disable(void)
{
        unsigned int cpu, cluster;
        struct bL_thread *t;
        struct task_struct *task;

        mutex_lock(&bL_switcher_activation_lock);
        lock_device_hotplug();

        if (!bL_switcher_active)
                goto out;

        if (bL_activation_notify(BL_NOTIFY_PRE_DISABLE) != 0) {
                bL_activation_notify(BL_NOTIFY_POST_ENABLE);
                goto out;
        }

        bL_switcher_active = 0;

        /*
         * To deactivate the switcher, we must shut down the switcher
         * threads to prevent any other requests from being accepted.
         * Then, if the final cluster for given logical CPU is not the
         * same as the original one, we'll recreate a switcher thread
         * just for the purpose of switching the CPU back without any
         * possibility for interference from external requests.
         */
        for_each_online_cpu(cpu) {
                t = &bL_threads[cpu];
                task = t->task;
                t->task = NULL;
                if (!task || IS_ERR(task))
                        continue;
                kthread_stop(task);
                /* no more switch may happen on this CPU at this point */
                cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
                if (cluster == bL_switcher_cpu_original_cluster[cpu])
                        continue;
                init_completion(&t->started);
                t->wanted_cluster = bL_switcher_cpu_original_cluster[cpu];
                task = bL_switcher_thread_create(cpu, t);
                if (!IS_ERR(task)) {
                        wait_for_completion(&t->started);
                        kthread_stop(task);
                        cluster = MPIDR_AFFINITY_LEVEL(cpu_logical_map(cpu), 1);
                        if (cluster == bL_switcher_cpu_original_cluster[cpu])
                                continue;
                }
                /* If execution gets here, we're in trouble. */
                pr_crit("%s: unable to restore original cluster for CPU %d\n",
                        __func__, cpu);
                pr_crit("%s: CPU %d can't be restored\n",
                        __func__, bL_switcher_cpu_pairing[cpu]);
                cpumask_clear_cpu(bL_switcher_cpu_pairing[cpu],
                                  &bL_switcher_removed_logical_cpus);
        }

        bL_switcher_restore_cpus();
        bL_switcher_trace_trigger();

        bL_activation_notify(BL_NOTIFY_POST_DISABLE);

out:
        unlock_device_hotplug();
        mutex_unlock(&bL_switcher_activation_lock);
}

static ssize_t bL_switcher_active_show(struct kobject *kobj,
                struct kobj_attribute *attr, char *buf)
{
        return sprintf(buf, "%u\n", bL_switcher_active);
}

static ssize_t bL_switcher_active_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t count)
{
        int ret;

        switch (buf[0]) {
        case '0':
                bL_switcher_disable();
                ret = 0;
                break;
        case '1':
                ret = bL_switcher_enable();
                break;
        default:
                ret = -EINVAL;
        }

        return (ret >= 0) ? count : ret;
}

static ssize_t bL_switcher_trace_trigger_store(struct kobject *kobj,
                struct kobj_attribute *attr, const char *buf, size_t count)
{
        int ret = bL_switcher_trace_trigger();

        return ret ? ret : count;
}

static struct kobj_attribute bL_switcher_active_attr =
        __ATTR(active, 0644, bL_switcher_active_show, bL_switcher_active_store);

static struct kobj_attribute bL_switcher_trace_trigger_attr =
        __ATTR(trace_trigger, 0200, NULL, bL_switcher_trace_trigger_store);

static struct attribute *bL_switcher_attrs[] = {
        &bL_switcher_active_attr.attr,
        &bL_switcher_trace_trigger_attr.attr,
        NULL,
};

static struct attribute_group bL_switcher_attr_group = {
        .attrs = bL_switcher_attrs,
};

static struct kobject *bL_switcher_kobj;

static int __init bL_switcher_sysfs_init(void)
{
        int ret;

        bL_switcher_kobj = kobject_create_and_add("bL_switcher", kernel_kobj);
        if (!bL_switcher_kobj)
                return -ENOMEM;
        ret = sysfs_create_group(bL_switcher_kobj, &bL_switcher_attr_group);
        if (ret)
                kobject_put(bL_switcher_kobj);
        return ret;
}

#endif  /* CONFIG_SYSFS */

bool bL_switcher_get_enabled(void)
{
        mutex_lock(&bL_switcher_activation_lock);

        return bL_switcher_active;
}
EXPORT_SYMBOL_GPL(bL_switcher_get_enabled);

void bL_switcher_put_enabled(void)
{
        mutex_unlock(&bL_switcher_activation_lock);
}
EXPORT_SYMBOL_GPL(bL_switcher_put_enabled);

/*
 * Veto any CPU hotplug operation on those CPUs we've removed
 * while the switcher is active.
 * We're just not ready to deal with that given the trickery involved.
 */
static int bL_switcher_cpu_pre(unsigned int cpu)
{
        int pairing;

        if (!bL_switcher_active)
                return 0;

        pairing = bL_switcher_cpu_pairing[cpu];

        if (pairing == -1)
                return -EINVAL;
        return 0;
}

static bool no_bL_switcher;
core_param(no_bL_switcher, no_bL_switcher, bool, 0644);

static int __init bL_switcher_init(void)
{
        int ret;

        if (!mcpm_is_available())
                return -ENODEV;

        cpuhp_setup_state_nocalls(CPUHP_ARM_BL_PREPARE, "arm/bl:prepare",
                                  bL_switcher_cpu_pre, NULL);
        ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "arm/bl:predown",
                                        NULL, bL_switcher_cpu_pre);
        if (ret < 0) {
                cpuhp_remove_state_nocalls(CPUHP_ARM_BL_PREPARE);
                pr_err("bL_switcher: Failed to allocate a hotplug state\n");
                return ret;
        }
        if (!no_bL_switcher) {
                ret = bL_switcher_enable();
                if (ret)
                        return ret;
        }

#ifdef CONFIG_SYSFS
        ret = bL_switcher_sysfs_init();
        if (ret)
                pr_err("%s: unable to create sysfs entry\n", __func__);
#endif

        return 0;
}

late_initcall(bL_switcher_init);