drivers/firmware/psci/psci_checker.c - linux/torvalds/linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  *
  * Copyright (C) 2016 ARM Limited
  */

 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

 #include <linux/atomic.h>
 #include <linux/completion.h>
 #include <linux/cpu.h>
 #include <linux/cpuidle.h>
 #include <linux/cpu_pm.h>
 #include <linux/kernel.h>
 #include <linux/kthread.h>
 #include <uapi/linux/sched/types.h>
 #include <linux/module.h>
 #include <linux/preempt.h>
 #include <linux/psci.h>
 #include <linux/slab.h>
 #include <linux/tick.h>
 #include <linux/topology.h>

 #include <asm/cpuidle.h>

 #include <uapi/linux/psci.h>

 #define NUM_SUSPEND_CYCLE (10)

 static unsigned int nb_available_cpus;
 static int tos_resident_cpu = -1;

 static atomic_t nb_active_threads;
 static struct completion suspend_threads_started =
 	COMPLETION_INITIALIZER(suspend_threads_started);
 static struct completion suspend_threads_done =
 	COMPLETION_INITIALIZER(suspend_threads_done);

 /*
  * We assume that PSCI operations are used if they are available. This is not
  * necessarily true on arm64, since the decision is based on the
  * "enable-method" property of each CPU in the DT, but given that there is no
  * arch-specific way to check this, we assume that the DT is sensible.
  */
 static int psci_ops_check(void)
 {
 	int migrate_type = -1;
 	int cpu;

 	if (!(psci_ops.cpu_off && psci_ops.cpu_on && psci_ops.cpu_suspend)) {
 		pr_warn("Missing PSCI operations, aborting tests\n");
 		return -EOPNOTSUPP;
 	}

 	if (psci_ops.migrate_info_type)
 		migrate_type = psci_ops.migrate_info_type();

 	if (migrate_type == PSCI_0_2_TOS_UP_MIGRATE ||
 	    migrate_type == PSCI_0_2_TOS_UP_NO_MIGRATE) {
 		/* There is a UP Trusted OS, find on which core it resides. */
 		for_each_online_cpu(cpu)
 			if (psci_tos_resident_on(cpu)) {
 				tos_resident_cpu = cpu;
 				break;
 			}
 		if (tos_resident_cpu == -1)
 			pr_warn("UP Trusted OS resides on no online CPU\n");
 	}

 	return 0;
 }

 /*
  * offlined_cpus is a temporary array but passing it as an argument avoids
  * multiple allocations.
  */
 static unsigned int down_and_up_cpus(const struct cpumask *cpus,
 				     struct cpumask *offlined_cpus)
 {
 	int cpu;
 	int err = 0;

 	cpumask_clear(offlined_cpus);

 	/* Try to power down all CPUs in the mask. */
 	for_each_cpu(cpu, cpus) {
 		int ret = remove_cpu(cpu);

 		/*
 		 * cpu_down() checks the number of online CPUs before the TOS
 		 * resident CPU.
 		 */
 		if (cpumask_weight(offlined_cpus) + 1 == nb_available_cpus) {
 			if (ret != -EBUSY) {
 				pr_err("Unexpected return code %d while trying "
 				       "to power down last online CPU %d\n",
 				       ret, cpu);
 				++err;
 			}
 		} else if (cpu == tos_resident_cpu) {
 			if (ret != -EPERM) {
 				pr_err("Unexpected return code %d while trying "
 				       "to power down TOS resident CPU %d\n",
 				       ret, cpu);
 				++err;
 			}
 		} else if (ret != 0) {
 			pr_err("Error occurred (%d) while trying "
 			       "to power down CPU %d\n", ret, cpu);
 			++err;
 		}

 		if (ret == 0)
 			cpumask_set_cpu(cpu, offlined_cpus);
 	}

 	/* Try to power up all the CPUs that have been offlined. */
 	for_each_cpu(cpu, offlined_cpus) {
 		int ret = add_cpu(cpu);

 		if (ret != 0) {
 			pr_err("Error occurred (%d) while trying "
 			       "to power up CPU %d\n", ret, cpu);
 			++err;
 		} else {
 			cpumask_clear_cpu(cpu, offlined_cpus);
 		}
 	}

 	/*
 	 * Something went bad at some point and some CPUs could not be turned
 	 * back on.
 	 */
 	WARN_ON(!cpumask_empty(offlined_cpus) ||
 		num_online_cpus() != nb_available_cpus);

 	return err;
 }

 static void free_cpu_groups(int num, cpumask_var_t **pcpu_groups)
 {
 	int i;
 	cpumask_var_t *cpu_groups = *pcpu_groups;

 	for (i = 0; i < num; ++i)
 		free_cpumask_var(cpu_groups[i]);
 	kfree(cpu_groups);
 }

 static int alloc_init_cpu_groups(cpumask_var_t **pcpu_groups)
 {
 	int num_groups = 0;
 	cpumask_var_t tmp, *cpu_groups;

 	if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
 		return -ENOMEM;

 	cpu_groups = kcalloc(nb_available_cpus, sizeof(cpu_groups),
 			     GFP_KERNEL);
 	if (!cpu_groups)
 		return -ENOMEM;

 	cpumask_copy(tmp, cpu_online_mask);

 	while (!cpumask_empty(tmp)) {
 		const struct cpumask *cpu_group =
 			topology_core_cpumask(cpumask_any(tmp));

 		if (!alloc_cpumask_var(&cpu_groups[num_groups], GFP_KERNEL)) {
 			free_cpu_groups(num_groups, &cpu_groups);
 			return -ENOMEM;
 		}
 		cpumask_copy(cpu_groups[num_groups++], cpu_group);
 		cpumask_andnot(tmp, tmp, cpu_group);
 	}

 	free_cpumask_var(tmp);
 	*pcpu_groups = cpu_groups;

 	return num_groups;
 }

 static int hotplug_tests(void)
 {
 	int i, nb_cpu_group, err = -ENOMEM;
 	cpumask_var_t offlined_cpus, *cpu_groups;
 	char *page_buf;

 	if (!alloc_cpumask_var(&offlined_cpus, GFP_KERNEL))
 		return err;

 	nb_cpu_group = alloc_init_cpu_groups(&cpu_groups);
 	if (nb_cpu_group < 0)
 		goto out_free_cpus;
 	page_buf = (char *)__get_free_page(GFP_KERNEL);
 	if (!page_buf)
 		goto out_free_cpu_groups;

 	err = 0;
 	/*
 	 * Of course the last CPU cannot be powered down and cpu_down() should
 	 * refuse doing that.
 	 */
 	pr_info("Trying to turn off and on again all CPUs\n");
 	err += down_and_up_cpus(cpu_online_mask, offlined_cpus);

 	/*
 	 * Take down CPUs by cpu group this time. When the last CPU is turned
 	 * off, the cpu group itself should shut down.
 	 */
 	for (i = 0; i < nb_cpu_group; ++i) {
 		ssize_t len = cpumap_print_to_pagebuf(true, page_buf,
 						      cpu_groups[i]);
 		/* Remove trailing newline. */
 		page_buf[len - 1] = '\0';
 		pr_info("Trying to turn off and on again group %d (CPUs %s)\n",
 			i, page_buf);
 		err += down_and_up_cpus(cpu_groups[i], offlined_cpus);
 	}

 	free_page((unsigned long)page_buf);
 out_free_cpu_groups:
 	free_cpu_groups(nb_cpu_group, &cpu_groups);
 out_free_cpus:
 	free_cpumask_var(offlined_cpus);
 	return err;
 }

 static void dummy_callback(struct timer_list *unused) {}

 static int suspend_cpu(struct cpuidle_device *dev,
 		       struct cpuidle_driver *drv, int index)
 {
 	struct cpuidle_state *state = &drv->states[index];
 	bool broadcast = state->flags & CPUIDLE_FLAG_TIMER_STOP;
 	int ret;

 	arch_cpu_idle_enter();

 	if (broadcast) {
 		/*
 		 * The local timer will be shut down, we need to enter tick
 		 * broadcast.
 		 */
 		ret = tick_broadcast_enter();
 		if (ret) {
 			/*
 			 * In the absence of hardware broadcast mechanism,
 			 * this CPU might be used to broadcast wakeups, which
 			 * may be why entering tick broadcast has failed.
 			 * There is little the kernel can do to work around
 			 * that, so enter WFI instead (idle state 0).
 			 */
 			cpu_do_idle();
 			ret = 0;
 			goto out_arch_exit;
 		}
 	}

 	ret = state->enter(dev, drv, index);

 	if (broadcast)
 		tick_broadcast_exit();

 out_arch_exit:
 	arch_cpu_idle_exit();

 	return ret;
 }

 static int suspend_test_thread(void *arg)
 {
 	int cpu = (long)arg;
 	int i, nb_suspend = 0, nb_shallow_sleep = 0, nb_err = 0;
 	struct sched_param sched_priority = { .sched_priority = MAX_RT_PRIO-1 };
 	struct cpuidle_device *dev;
 	struct cpuidle_driver *drv;
 	/* No need for an actual callback, we just want to wake up the CPU. */
 	struct timer_list wakeup_timer;

 	/* Wait for the main thread to give the start signal. */
 	wait_for_completion(&suspend_threads_started);

 	/* Set maximum priority to preempt all other threads on this CPU. */
 	if (sched_setscheduler_nocheck(current, SCHED_FIFO, &sched_priority))
 		pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
 			cpu);

 	dev = this_cpu_read(cpuidle_devices);
 	drv = cpuidle_get_cpu_driver(dev);

 	pr_info("CPU %d entering suspend cycles, states 1 through %d\n",
 		cpu, drv->state_count - 1);

 	timer_setup_on_stack(&wakeup_timer, dummy_callback, 0);
 	for (i = 0; i < NUM_SUSPEND_CYCLE; ++i) {
 		int index;
 		/*
 		 * Test all possible states, except 0 (which is usually WFI and
 		 * doesn't use PSCI).
 		 */
 		for (index = 1; index < drv->state_count; ++index) {
 			int ret;
 			struct cpuidle_state *state = &drv->states[index];

 			/*
 			 * Set the timer to wake this CPU up in some time (which
 			 * should be largely sufficient for entering suspend).
 			 * If the local tick is disabled when entering suspend,
 			 * suspend_cpu() takes care of switching to a broadcast
 			 * tick, so the timer will still wake us up.
 			 */
 			mod_timer(&wakeup_timer, jiffies +
 				  usecs_to_jiffies(state->target_residency));

 			/* IRQs must be disabled during suspend operations. */
 			local_irq_disable();

 			ret = suspend_cpu(dev, drv, index);

 			/*
 			 * We have woken up. Re-enable IRQs to handle any
 			 * pending interrupt, do not wait until the end of the
 			 * loop.
 			 */
 			local_irq_enable();

 			if (ret == index) {
 				++nb_suspend;
 			} else if (ret >= 0) {
 				/* We did not enter the expected state. */
 				++nb_shallow_sleep;
 			} else {
 				pr_err("Failed to suspend CPU %d: error %d "
 				       "(requested state %d, cycle %d)\n",
 				       cpu, ret, index, i);
 				++nb_err;
 			}
 		}
 	}

 	/*
 	 * Disable the timer to make sure that the timer will not trigger
 	 * later.
 	 */
 	del_timer(&wakeup_timer);
 	destroy_timer_on_stack(&wakeup_timer);

 	if (atomic_dec_return_relaxed(&nb_active_threads) == 0)
 		complete(&suspend_threads_done);

 	/* Give up on RT scheduling and wait for termination. */
 	sched_priority.sched_priority = 0;
 	if (sched_setscheduler_nocheck(current, SCHED_NORMAL, &sched_priority))
 		pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
 			cpu);
 	for (;;) {
 		/* Needs to be set first to avoid missing a wakeup. */
 		set_current_state(TASK_INTERRUPTIBLE);
 		if (kthread_should_park())
 			break;
 		schedule();
 	}

 	pr_info("CPU %d suspend test results: success %d, shallow states %d, errors %d\n",
 		cpu, nb_suspend, nb_shallow_sleep, nb_err);

 	kthread_parkme();

 	return nb_err;
 }

 static int suspend_tests(void)
 {
 	int i, cpu, err = 0;
 	struct task_struct **threads;
 	int nb_threads = 0;

 	threads = kmalloc_array(nb_available_cpus, sizeof(*threads),
 				GFP_KERNEL);
 	if (!threads)
 		return -ENOMEM;

 	/*
 	 * Stop cpuidle to prevent the idle tasks from entering a deep sleep
 	 * mode, as it might interfere with the suspend threads on other CPUs.
 	 * This does not prevent the suspend threads from using cpuidle (only
 	 * the idle tasks check this status). Take the idle lock so that
 	 * the cpuidle driver and device look-up can be carried out safely.
 	 */
 	cpuidle_pause_and_lock();

 	for_each_online_cpu(cpu) {
 		struct task_struct *thread;
 		/* Check that cpuidle is available on that CPU. */
 		struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
 		struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);

 		if (!dev || !drv) {
 			pr_warn("cpuidle not available on CPU %d, ignoring\n",
 				cpu);
 			continue;
 		}

 		thread = kthread_create_on_cpu(suspend_test_thread,
 					       (void *)(long)cpu, cpu,
 					       "psci_suspend_test");
 		if (IS_ERR(thread))
 			pr_err("Failed to create kthread on CPU %d\n", cpu);
 		else
 			threads[nb_threads++] = thread;
 	}

 	if (nb_threads < 1) {
 		err = -ENODEV;
 		goto out;
 	}

 	atomic_set(&nb_active_threads, nb_threads);

 	/*
 	 * Wake up the suspend threads. To avoid the main thread being preempted
 	 * before all the threads have been unparked, the suspend threads will
 	 * wait for the completion of suspend_threads_started.
 	 */
 	for (i = 0; i < nb_threads; ++i)
 		wake_up_process(threads[i]);
 	complete_all(&suspend_threads_started);

 	wait_for_completion(&suspend_threads_done);


 	/* Stop and destroy all threads, get return status. */
 	for (i = 0; i < nb_threads; ++i) {
 		err += kthread_park(threads[i]);
 		err += kthread_stop(threads[i]);
 	}
  out:
 	cpuidle_resume_and_unlock();
 	kfree(threads);
 	return err;
 }

 static int __init psci_checker(void)
 {
 	int ret;

 	/*
 	 * Since we're in an initcall, we assume that all the CPUs that all
 	 * CPUs that can be onlined have been onlined.
 	 *
 	 * The tests assume that hotplug is enabled but nobody else is using it,
 	 * otherwise the results will be unpredictable. However, since there
 	 * is no userspace yet in initcalls, that should be fine, as long as
 	 * no torture test is running at the same time (see Kconfig).
 	 */
 	nb_available_cpus = num_online_cpus();

 	/* Check PSCI operations are set up and working. */
 	ret = psci_ops_check();
 	if (ret)
 		return ret;

 	pr_info("PSCI checker started using %u CPUs\n", nb_available_cpus);

 	pr_info("Starting hotplug tests\n");
 	ret = hotplug_tests();
 	if (ret == 0)
 		pr_info("Hotplug tests passed OK\n");
 	else if (ret > 0)
 		pr_err("%d error(s) encountered in hotplug tests\n", ret);
 	else {
 		pr_err("Out of memory\n");
 		return ret;
 	}

 	pr_info("Starting suspend tests (%d cycles per state)\n",
 		NUM_SUSPEND_CYCLE);
 	ret = suspend_tests();
 	if (ret == 0)
 		pr_info("Suspend tests passed OK\n");
 	else if (ret > 0)
 		pr_err("%d error(s) encountered in suspend tests\n", ret);
 	else {
 		switch (ret) {
 		case -ENOMEM:
 			pr_err("Out of memory\n");
 			break;
 		case -ENODEV:
 			pr_warn("Could not start suspend tests on any CPU\n");
 			break;
 		}
 	}

 	pr_info("PSCI checker completed\n");
 	return ret < 0 ? ret : 0;
 }
 late_initcall(psci_checker);
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	*
	* Copyright (C) 2016 ARM Limited
	*/

	#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

	#include <linux/atomic.h>
	#include <linux/completion.h>
	#include <linux/cpu.h>
	#include <linux/cpuidle.h>
	#include <linux/cpu_pm.h>
	#include <linux/kernel.h>
	#include <linux/kthread.h>
	#include <uapi/linux/sched/types.h>
	#include <linux/module.h>
	#include <linux/preempt.h>
	#include <linux/psci.h>
	#include <linux/slab.h>
	#include <linux/tick.h>
	#include <linux/topology.h>

	#include <asm/cpuidle.h>

	#include <uapi/linux/psci.h>

	#define NUM_SUSPEND_CYCLE (10)

	static unsigned int nb_available_cpus;
	static int tos_resident_cpu = -1;

	static atomic_t nb_active_threads;
	static struct completion suspend_threads_started =
	COMPLETION_INITIALIZER(suspend_threads_started);
	static struct completion suspend_threads_done =
	COMPLETION_INITIALIZER(suspend_threads_done);

	/*
	* We assume that PSCI operations are used if they are available. This is not
	* necessarily true on arm64, since the decision is based on the
	* "enable-method" property of each CPU in the DT, but given that there is no
	* arch-specific way to check this, we assume that the DT is sensible.
	*/
	static int psci_ops_check(void)
	{
	int migrate_type = -1;
	int cpu;

	if (!(psci_ops.cpu_off && psci_ops.cpu_on && psci_ops.cpu_suspend)) {
	pr_warn("Missing PSCI operations, aborting tests\n");
	return -EOPNOTSUPP;
	}

	if (psci_ops.migrate_info_type)
	migrate_type = psci_ops.migrate_info_type();

	if (migrate_type == PSCI_0_2_TOS_UP_MIGRATE \|\|
	migrate_type == PSCI_0_2_TOS_UP_NO_MIGRATE) {
	/* There is a UP Trusted OS, find on which core it resides. */
	for_each_online_cpu(cpu)
	if (psci_tos_resident_on(cpu)) {
	tos_resident_cpu = cpu;
	break;
	}
	if (tos_resident_cpu == -1)
	pr_warn("UP Trusted OS resides on no online CPU\n");
	}

	return 0;
	}

	/*
	* offlined_cpus is a temporary array but passing it as an argument avoids
	* multiple allocations.
	*/
	static unsigned int down_and_up_cpus(const struct cpumask *cpus,
	struct cpumask *offlined_cpus)
	{
	int cpu;
	int err = 0;

	cpumask_clear(offlined_cpus);

	/* Try to power down all CPUs in the mask. */
	for_each_cpu(cpu, cpus) {
	int ret = remove_cpu(cpu);

	/*
	* cpu_down() checks the number of online CPUs before the TOS
	* resident CPU.
	*/
	if (cpumask_weight(offlined_cpus) + 1 == nb_available_cpus) {
	if (ret != -EBUSY) {
	pr_err("Unexpected return code %d while trying "
	"to power down last online CPU %d\n",
	ret, cpu);
	++err;
	}
	} else if (cpu == tos_resident_cpu) {
	if (ret != -EPERM) {
	pr_err("Unexpected return code %d while trying "
	"to power down TOS resident CPU %d\n",
	ret, cpu);
	++err;
	}
	} else if (ret != 0) {
	pr_err("Error occurred (%d) while trying "
	"to power down CPU %d\n", ret, cpu);
	++err;
	}

	if (ret == 0)
	cpumask_set_cpu(cpu, offlined_cpus);
	}

	/* Try to power up all the CPUs that have been offlined. */
	for_each_cpu(cpu, offlined_cpus) {
	int ret = add_cpu(cpu);

	if (ret != 0) {
	pr_err("Error occurred (%d) while trying "
	"to power up CPU %d\n", ret, cpu);
	++err;
	} else {
	cpumask_clear_cpu(cpu, offlined_cpus);
	}
	}

	/*
	* Something went bad at some point and some CPUs could not be turned
	* back on.
	*/
	WARN_ON(!cpumask_empty(offlined_cpus) \|\|
	num_online_cpus() != nb_available_cpus);

	return err;
	}

	static void free_cpu_groups(int num, cpumask_var_t **pcpu_groups)
	{
	int i;
	cpumask_var_t cpu_groups = pcpu_groups;

	for (i = 0; i < num; ++i)
	free_cpumask_var(cpu_groups[i]);
	kfree(cpu_groups);
	}

	static int alloc_init_cpu_groups(cpumask_var_t **pcpu_groups)
	{
	int num_groups = 0;
	cpumask_var_t tmp, *cpu_groups;

	if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
	return -ENOMEM;

	cpu_groups = kcalloc(nb_available_cpus, sizeof(cpu_groups),
	GFP_KERNEL);
	if (!cpu_groups)
	return -ENOMEM;

	cpumask_copy(tmp, cpu_online_mask);

	while (!cpumask_empty(tmp)) {
	const struct cpumask *cpu_group =
	topology_core_cpumask(cpumask_any(tmp));

	if (!alloc_cpumask_var(&cpu_groups[num_groups], GFP_KERNEL)) {
	free_cpu_groups(num_groups, &cpu_groups);
	return -ENOMEM;
	}
	cpumask_copy(cpu_groups[num_groups++], cpu_group);
	cpumask_andnot(tmp, tmp, cpu_group);
	}

	free_cpumask_var(tmp);
	*pcpu_groups = cpu_groups;

	return num_groups;
	}

	static int hotplug_tests(void)
	{
	int i, nb_cpu_group, err = -ENOMEM;
	cpumask_var_t offlined_cpus, *cpu_groups;
	char *page_buf;

	if (!alloc_cpumask_var(&offlined_cpus, GFP_KERNEL))
	return err;

	nb_cpu_group = alloc_init_cpu_groups(&cpu_groups);
	if (nb_cpu_group < 0)
	goto out_free_cpus;
	page_buf = (char *)__get_free_page(GFP_KERNEL);
	if (!page_buf)
	goto out_free_cpu_groups;

	err = 0;
	/*
	* Of course the last CPU cannot be powered down and cpu_down() should
	* refuse doing that.
	*/
	pr_info("Trying to turn off and on again all CPUs\n");
	err += down_and_up_cpus(cpu_online_mask, offlined_cpus);

	/*
	* Take down CPUs by cpu group this time. When the last CPU is turned
	* off, the cpu group itself should shut down.
	*/
	for (i = 0; i < nb_cpu_group; ++i) {
	ssize_t len = cpumap_print_to_pagebuf(true, page_buf,
	cpu_groups[i]);
	/* Remove trailing newline. */
	page_buf[len - 1] = '\0';
	pr_info("Trying to turn off and on again group %d (CPUs %s)\n",
	i, page_buf);
	err += down_and_up_cpus(cpu_groups[i], offlined_cpus);
	}

	free_page((unsigned long)page_buf);
	out_free_cpu_groups:
	free_cpu_groups(nb_cpu_group, &cpu_groups);
	out_free_cpus:
	free_cpumask_var(offlined_cpus);
	return err;
	}

	static void dummy_callback(struct timer_list *unused) {}

	static int suspend_cpu(struct cpuidle_device *dev,
	struct cpuidle_driver *drv, int index)
	{
	struct cpuidle_state *state = &drv->states[index];
	bool broadcast = state->flags & CPUIDLE_FLAG_TIMER_STOP;
	int ret;

	arch_cpu_idle_enter();

	if (broadcast) {
	/*
	* The local timer will be shut down, we need to enter tick
	* broadcast.
	*/
	ret = tick_broadcast_enter();
	if (ret) {
	/*
	* In the absence of hardware broadcast mechanism,
	* this CPU might be used to broadcast wakeups, which
	* may be why entering tick broadcast has failed.
	* There is little the kernel can do to work around
	* that, so enter WFI instead (idle state 0).
	*/
	cpu_do_idle();
	ret = 0;
	goto out_arch_exit;
	}
	}

	ret = state->enter(dev, drv, index);

	if (broadcast)
	tick_broadcast_exit();

	out_arch_exit:
	arch_cpu_idle_exit();

	return ret;
	}

	static int suspend_test_thread(void *arg)
	{
	int cpu = (long)arg;
	int i, nb_suspend = 0, nb_shallow_sleep = 0, nb_err = 0;
	struct sched_param sched_priority = { .sched_priority = MAX_RT_PRIO-1 };
	struct cpuidle_device *dev;
	struct cpuidle_driver *drv;
	/* No need for an actual callback, we just want to wake up the CPU. */
	struct timer_list wakeup_timer;

	/* Wait for the main thread to give the start signal. */
	wait_for_completion(&suspend_threads_started);

	/* Set maximum priority to preempt all other threads on this CPU. */
	if (sched_setscheduler_nocheck(current, SCHED_FIFO, &sched_priority))
	pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
	cpu);

	dev = this_cpu_read(cpuidle_devices);
	drv = cpuidle_get_cpu_driver(dev);

	pr_info("CPU %d entering suspend cycles, states 1 through %d\n",
	cpu, drv->state_count - 1);

	timer_setup_on_stack(&wakeup_timer, dummy_callback, 0);
	for (i = 0; i < NUM_SUSPEND_CYCLE; ++i) {
	int index;
	/*
	* Test all possible states, except 0 (which is usually WFI and
	* doesn't use PSCI).
	*/
	for (index = 1; index < drv->state_count; ++index) {
	int ret;
	struct cpuidle_state *state = &drv->states[index];

	/*
	* Set the timer to wake this CPU up in some time (which
	* should be largely sufficient for entering suspend).
	* If the local tick is disabled when entering suspend,
	* suspend_cpu() takes care of switching to a broadcast
	* tick, so the timer will still wake us up.
	*/
	mod_timer(&wakeup_timer, jiffies +
	usecs_to_jiffies(state->target_residency));

	/* IRQs must be disabled during suspend operations. */
	local_irq_disable();

	ret = suspend_cpu(dev, drv, index);

	/*
	* We have woken up. Re-enable IRQs to handle any
	* pending interrupt, do not wait until the end of the
	* loop.
	*/
	local_irq_enable();

	if (ret == index) {
	++nb_suspend;
	} else if (ret >= 0) {
	/* We did not enter the expected state. */
	++nb_shallow_sleep;
	} else {
	pr_err("Failed to suspend CPU %d: error %d "
	"(requested state %d, cycle %d)\n",
	cpu, ret, index, i);
	++nb_err;
	}
	}
	}

	/*
	* Disable the timer to make sure that the timer will not trigger
	* later.
	*/
	del_timer(&wakeup_timer);
	destroy_timer_on_stack(&wakeup_timer);

	if (atomic_dec_return_relaxed(&nb_active_threads) == 0)
	complete(&suspend_threads_done);

	/* Give up on RT scheduling and wait for termination. */
	sched_priority.sched_priority = 0;
	if (sched_setscheduler_nocheck(current, SCHED_NORMAL, &sched_priority))
	pr_warn("Failed to set suspend thread scheduler on CPU %d\n",
	cpu);
	for (;;) {
	/* Needs to be set first to avoid missing a wakeup. */
	set_current_state(TASK_INTERRUPTIBLE);
	if (kthread_should_park())
	break;
	schedule();
	}

	pr_info("CPU %d suspend test results: success %d, shallow states %d, errors %d\n",
	cpu, nb_suspend, nb_shallow_sleep, nb_err);

	kthread_parkme();

	return nb_err;
	}

	static int suspend_tests(void)
	{
	int i, cpu, err = 0;
	struct task_struct **threads;
	int nb_threads = 0;

	threads = kmalloc_array(nb_available_cpus, sizeof(*threads),
	GFP_KERNEL);
	if (!threads)
	return -ENOMEM;

	/*
	* Stop cpuidle to prevent the idle tasks from entering a deep sleep
	* mode, as it might interfere with the suspend threads on other CPUs.
	* This does not prevent the suspend threads from using cpuidle (only
	* the idle tasks check this status). Take the idle lock so that
	* the cpuidle driver and device look-up can be carried out safely.
	*/
	cpuidle_pause_and_lock();

	for_each_online_cpu(cpu) {
	struct task_struct *thread;
	/* Check that cpuidle is available on that CPU. */
	struct cpuidle_device *dev = per_cpu(cpuidle_devices, cpu);
	struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev);

	if (!dev \|\| !drv) {
	pr_warn("cpuidle not available on CPU %d, ignoring\n",
	cpu);
	continue;
	}

	thread = kthread_create_on_cpu(suspend_test_thread,
	(void *)(long)cpu, cpu,
	"psci_suspend_test");
	if (IS_ERR(thread))
	pr_err("Failed to create kthread on CPU %d\n", cpu);
	else
	threads[nb_threads++] = thread;
	}

	if (nb_threads < 1) {
	err = -ENODEV;
	goto out;
	}

	atomic_set(&nb_active_threads, nb_threads);

	/*
	* Wake up the suspend threads. To avoid the main thread being preempted
	* before all the threads have been unparked, the suspend threads will
	* wait for the completion of suspend_threads_started.
	*/
	for (i = 0; i < nb_threads; ++i)
	wake_up_process(threads[i]);
	complete_all(&suspend_threads_started);

	wait_for_completion(&suspend_threads_done);


	/* Stop and destroy all threads, get return status. */
	for (i = 0; i < nb_threads; ++i) {
	err += kthread_park(threads[i]);
	err += kthread_stop(threads[i]);
	}
	out:
	cpuidle_resume_and_unlock();
	kfree(threads);
	return err;
	}

	static int __init psci_checker(void)
	{
	int ret;

	/*
	* Since we're in an initcall, we assume that all the CPUs that all
	* CPUs that can be onlined have been onlined.
	*
	* The tests assume that hotplug is enabled but nobody else is using it,
	* otherwise the results will be unpredictable. However, since there
	* is no userspace yet in initcalls, that should be fine, as long as
	* no torture test is running at the same time (see Kconfig).
	*/
	nb_available_cpus = num_online_cpus();

	/* Check PSCI operations are set up and working. */
	ret = psci_ops_check();
	if (ret)
	return ret;

	pr_info("PSCI checker started using %u CPUs\n", nb_available_cpus);

	pr_info("Starting hotplug tests\n");
	ret = hotplug_tests();
	if (ret == 0)
	pr_info("Hotplug tests passed OK\n");
	else if (ret > 0)
	pr_err("%d error(s) encountered in hotplug tests\n", ret);
	else {
	pr_err("Out of memory\n");
	return ret;
	}

	pr_info("Starting suspend tests (%d cycles per state)\n",
	NUM_SUSPEND_CYCLE);
	ret = suspend_tests();
	if (ret == 0)
	pr_info("Suspend tests passed OK\n");
	else if (ret > 0)
	pr_err("%d error(s) encountered in suspend tests\n", ret);
	else {
	switch (ret) {
	case -ENOMEM:
	pr_err("Out of memory\n");
	break;
	case -ENODEV:
	pr_warn("Could not start suspend tests on any CPU\n");
	break;
	}
	}

	pr_info("PSCI checker completed\n");
	return ret < 0 ? ret : 0;
	}
	late_initcall(psci_checker);