drivers: psci: PSCI checker module

On arm and arm64, PSCI is one of the possible firmware interfaces
used for power management. This includes both turning CPUs on and off,
and suspending them (entering idle states).

This patch adds a PSCI checker module that enables basic testing of
PSCI operations during startup. There are two main tests: CPU
hotplugging and suspending.

In the hotplug tests, the hotplug API is used to turn off and on again
all CPUs in the system, and then all CPUs in each cluster, checking
the consistency of the return codes.

In the suspend tests, a high-priority thread is created on each core
and uses low-level cpuidle functionalities to enter suspend, in all
the possible states and multiple times. This should allow a maximum
number of CPUs to enter the same sleep state at the same or slightly
different time.

In essence, the suspend tests use a principle similar to that of the
intel_powerclamp driver (drivers/thermal/intel_powerclamp.c), but the
threads are only kept for the duration of the test (they are already
gone when userspace is started) and it does not require to stop/start
the tick.

While in theory power management PSCI functions (CPU_{ON,OFF,SUSPEND})
could be directly called, this proved too difficult as it would imply
the duplication of all the logic used by the kernel to allow for a
clean shutdown/bringup/suspend of the CPU (the deepest sleep states
implying potentially the shutdown of the CPU).

Note that this file cannot be compiled as a loadable module, since it
uses a number of non-exported identifiers (essentially for
PSCI-specific checks and direct use of cpuidle) and relies on the
absence of userspace to avoid races when calling hotplug and cpuidle
functions.

For now at least, CONFIG_PSCI_CHECKER is mutually exclusive with
CONFIG_TORTURE_TEST, because torture tests may also use hotplug and
cause false positives in the hotplug tests.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Kevin Hilman <khilman@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Acked-by: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> [torture test config]
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
[lpieralisi: added cpuidle locking, reworded commit log/kconfig entry]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/firmware/Kconfig

@@ -8,6 +8,17 @@ menu "Firmware Drivers"
 config ARM_PSCI_FW
 	bool
 
+config ARM_PSCI_CHECKER
+	bool "ARM PSCI checker"
+	depends on ARM_PSCI_FW && HOTPLUG_CPU && !TORTURE_TEST
+	help
+	  Run the PSCI checker during startup. This checks that hotplug and
+	  suspend operations work correctly when using PSCI.
+
+	  The torture tests may interfere with the PSCI checker by turning CPUs
+	  on and off through hotplug, so for now torture tests and PSCI checker
+	  are mutually exclusive.
+
 config ARM_SCPI_PROTOCOL
 	tristate "ARM System Control and Power Interface (SCPI) Message Protocol"
 	depends on MAILBOX

drivers/firmware/Makefile

@@ -2,6 +2,7 @@
 # Makefile for the linux kernel.
 #
 obj-$(CONFIG_ARM_PSCI_FW)	+= psci.o
+obj-$(CONFIG_ARM_PSCI_CHECKER)	+= psci_checker.o
 obj-$(CONFIG_ARM_SCPI_PROTOCOL)	+= arm_scpi.o
 obj-$(CONFIG_ARM_SCPI_POWER_DOMAIN) += scpi_pm_domain.o
 obj-$(CONFIG_DMI)		+= dmi_scan.o

drivers/firmware/psci_checker.c

@@ -0,0 +1,490 @@
+/*
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed 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.
+ *
+ * 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 <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;
+}
+
+static int find_clusters(const struct cpumask *cpus,
+			 const struct cpumask **clusters)
+{
+	unsigned int nb = 0;
+	cpumask_var_t tmp;
+
+	if (!alloc_cpumask_var(&tmp, GFP_KERNEL))
+		return -ENOMEM;
+	cpumask_copy(tmp, cpus);
+
+	while (!cpumask_empty(tmp)) {
+		const struct cpumask *cluster =
+			topology_core_cpumask(cpumask_any(tmp));
+
+		clusters[nb++] = cluster;
+		cpumask_andnot(tmp, tmp, cluster);
+	}
+
+	free_cpumask_var(tmp);
+	return nb;
+}
+
+/*
+ * 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 = cpu_down(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 = cpu_up(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 int hotplug_tests(void)
+{
+	int err;
+	cpumask_var_t offlined_cpus;
+	int i, nb_cluster;
+	const struct cpumask **clusters;
+	char *page_buf;
+
+	err = -ENOMEM;
+	if (!alloc_cpumask_var(&offlined_cpus, GFP_KERNEL))
+		return err;
+	/* We may have up to nb_available_cpus clusters. */
+	clusters = kmalloc_array(nb_available_cpus, sizeof(*clusters),
+				 GFP_KERNEL);
+	if (!clusters)
+		goto out_free_cpus;
+	page_buf = (char *)__get_free_page(GFP_KERNEL);
+	if (!page_buf)
+		goto out_free_clusters;
+
+	err = 0;
+	nb_cluster = find_clusters(cpu_online_mask, clusters);
+
+	/*
+	 * 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 cluster this time. When the last CPU is turned
+	 * off, the cluster itself should shut down.
+	 */
+	for (i = 0; i < nb_cluster; ++i) {
+		int cluster_id =
+			topology_physical_package_id(cpumask_any(clusters[i]));
+		ssize_t len = cpumap_print_to_pagebuf(true, page_buf,
+						      clusters[i]);
+		/* Remove trailing newline. */
+		page_buf[len - 1] = '\0';
+		pr_info("Trying to turn off and on again cluster %d "
+			"(CPUs %s)\n", cluster_id, page_buf);
+		err += down_and_up_cpus(clusters[i], offlined_cpus);
+	}
+
+	free_page((unsigned long)page_buf);
+out_free_clusters:
+	kfree(clusters);
+out_free_cpus:
+	free_cpumask_var(offlined_cpus);
+	return err;
+}
+
+static void dummy_callback(unsigned long ignored) {}
+
+static int suspend_cpu(int index, bool broadcast)
+{
+	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;
+		}
+	}
+
+	/*
+	 * Replicate the common ARM cpuidle enter function
+	 * (arm_enter_idle_state).
+	 */
+	ret = CPU_PM_CPU_IDLE_ENTER(arm_cpuidle_suspend, 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 =
+		TIMER_INITIALIZER(dummy_callback, 0, 0);
+
+	/* 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);
+
+	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) {
+			struct cpuidle_state *state = &drv->states[index];
+			bool broadcast = state->flags & CPUIDLE_FLAG_TIMER_STOP;
+			int ret;
+
+			/*
+			 * 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(index, broadcast);
+
+			/*
+			 * 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);
+
+	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_stop()) {
+			__set_current_state(TASK_RUNNING);
+			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);
+
+	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_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);