drivers/cpuidle/driver.c

/*
 * driver.c - driver support
 *
 * (C) 2006-2007 Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
 *               Shaohua Li <shaohua.li@intel.com>
 *               Adam Belay <abelay@novell.com>
 *
 * This code is licenced under the GPL.
 */

#include <linux/mutex.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/sched/idle.h>
#include <linux/cpuidle.h>
#include <linux/cpumask.h>
#include <linux/tick.h>
#include <linux/cpu.h>

#include "cpuidle.h"

DEFINE_SPINLOCK(cpuidle_driver_lock);

#ifdef CONFIG_CPU_IDLE_MULTIPLE_DRIVERS

static DEFINE_PER_CPU(struct cpuidle_driver *, cpuidle_drivers);

/**
 * __cpuidle_get_cpu_driver - return the cpuidle driver tied to a CPU.
 * @cpu: the CPU handled by the driver
 *
 * Returns a pointer to struct cpuidle_driver or NULL if no driver has been
 * registered for @cpu.
 */
static struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
{
	return per_cpu(cpuidle_drivers, cpu);
}

/**
 * __cpuidle_unset_driver - unset per CPU driver variables.
 * @drv: a valid pointer to a struct cpuidle_driver
 *
 * For each CPU in the driver's CPU mask, unset the registered driver per CPU
 * variable. If @drv is different from the registered driver, the corresponding
 * variable is not cleared.
 */
static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
{
	int cpu;

	for_each_cpu(cpu, drv->cpumask) {

		if (drv != __cpuidle_get_cpu_driver(cpu))
			continue;

		per_cpu(cpuidle_drivers, cpu) = NULL;
	}
}

/**
 * __cpuidle_set_driver - set per CPU driver variables for the given driver.
 * @drv: a valid pointer to a struct cpuidle_driver
 *
 * For each CPU in the driver's cpumask, unset the registered driver per CPU
 * to @drv.
 *
 * Returns 0 on success, -EBUSY if the CPUs have driver(s) already.
 */
static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
{
	int cpu;

	for_each_cpu(cpu, drv->cpumask) {

		if (__cpuidle_get_cpu_driver(cpu)) {
			__cpuidle_unset_driver(drv);
			return -EBUSY;
		}

		per_cpu(cpuidle_drivers, cpu) = drv;
	}

	return 0;
}

#else

static struct cpuidle_driver *cpuidle_curr_driver;

/**
 * __cpuidle_get_cpu_driver - return the global cpuidle driver pointer.
 * @cpu: ignored without the multiple driver support
 *
 * Return a pointer to a struct cpuidle_driver object or NULL if no driver was
 * previously registered.
 */
static inline struct cpuidle_driver *__cpuidle_get_cpu_driver(int cpu)
{
	return cpuidle_curr_driver;
}

/**
 * __cpuidle_set_driver - assign the global cpuidle driver variable.
 * @drv: pointer to a struct cpuidle_driver object
 *
 * Returns 0 on success, -EBUSY if the driver is already registered.
 */
static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
{
	if (cpuidle_curr_driver)
		return -EBUSY;

	cpuidle_curr_driver = drv;

	return 0;
}

/**
 * __cpuidle_unset_driver - unset the global cpuidle driver variable.
 * @drv: a pointer to a struct cpuidle_driver
 *
 * Reset the global cpuidle variable to NULL.  If @drv does not match the
 * registered driver, do nothing.
 */
static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
{
	if (drv == cpuidle_curr_driver)
		cpuidle_curr_driver = NULL;
}

#endif

/**
 * cpuidle_setup_broadcast_timer - enable/disable the broadcast timer on a cpu
 * @arg: a void pointer used to match the SMP cross call API
 *
 * If @arg is NULL broadcast is disabled otherwise enabled
 *
 * This function is executed per CPU by an SMP cross call.  It's not
 * supposed to be called directly.
 */
static void cpuidle_setup_broadcast_timer(void *arg)
{
	if (arg)
		tick_broadcast_enable();
	else
		tick_broadcast_disable();
}

/**
 * __cpuidle_driver_init - initialize the driver's internal data
 * @drv: a valid pointer to a struct cpuidle_driver
 */
static void __cpuidle_driver_init(struct cpuidle_driver *drv)
{
	int i;

	drv->refcnt = 0;

	/*
	 * Use all possible CPUs as the default, because if the kernel boots
	 * with some CPUs offline and then we online one of them, the CPU
	 * notifier has to know which driver to assign.
	 */
	if (!drv->cpumask)
		drv->cpumask = (struct cpumask *)cpu_possible_mask;

	/*
	 * Look for the timer stop flag in the different states, so that we know
	 * if the broadcast timer has to be set up.  The loop is in the reverse
	 * order, because usually one of the deeper states have this flag set.
	 */
	for (i = drv->state_count - 1; i >= 0 ; i--) {
		if (drv->states[i].flags & CPUIDLE_FLAG_TIMER_STOP) {
			drv->bctimer = 1;
			break;
		}
	}
}

/**
 * __cpuidle_register_driver: register the driver
 * @drv: a valid pointer to a struct cpuidle_driver
 *
 * Do some sanity checks, initialize the driver, assign the driver to the
 * global cpuidle driver variable(s) and set up the broadcast timer if the
 * cpuidle driver has some states that shut down the local timer.
 *
 * Returns 0 on success, a negative error code otherwise:
 *  * -EINVAL if the driver pointer is NULL or no idle states are available
 *  * -ENODEV if the cpuidle framework is disabled
 *  * -EBUSY if the driver is already assigned to the global variable(s)
 */
static int __cpuidle_register_driver(struct cpuidle_driver *drv)
{
	int ret;

	if (!drv || !drv->state_count)
		return -EINVAL;

	ret = cpuidle_coupled_state_verify(drv);
	if (ret)
		return ret;

	if (cpuidle_disabled())
		return -ENODEV;

	__cpuidle_driver_init(drv);

	ret = __cpuidle_set_driver(drv);
	if (ret)
		return ret;

	if (drv->bctimer)
		on_each_cpu_mask(drv->cpumask, cpuidle_setup_broadcast_timer,
				 (void *)1, 1);

	return 0;
}

/**
 * __cpuidle_unregister_driver - unregister the driver
 * @drv: a valid pointer to a struct cpuidle_driver
 *
 * Check if the driver is no longer in use, reset the global cpuidle driver
 * variable(s) and disable the timer broadcast notification mechanism if it was
 * in use.
 *
 */
static void __cpuidle_unregister_driver(struct cpuidle_driver *drv)
{
	if (WARN_ON(drv->refcnt > 0))
		return;

	if (drv->bctimer) {
		drv->bctimer = 0;
		on_each_cpu_mask(drv->cpumask, cpuidle_setup_broadcast_timer,
				 NULL, 1);
	}

	__cpuidle_unset_driver(drv);
}

/**
 * cpuidle_register_driver - registers a driver
 * @drv: a pointer to a valid struct cpuidle_driver
 *
 * Register the driver under a lock to prevent concurrent attempts to
 * [un]register the driver from occuring at the same time.
 *
 * Returns 0 on success, a negative error code (returned by
 * __cpuidle_register_driver()) otherwise.
 */
int cpuidle_register_driver(struct cpuidle_driver *drv)
{
	struct cpuidle_governor *gov;
	int ret;

	spin_lock(&cpuidle_driver_lock);
	ret = __cpuidle_register_driver(drv);
	spin_unlock(&cpuidle_driver_lock);

	if (!ret && !strlen(param_governor) && drv->governor &&
	    (cpuidle_get_driver() == drv)) {
		mutex_lock(&cpuidle_lock);
		gov = cpuidle_find_governor(drv->governor);
		if (gov) {
			cpuidle_prev_governor = cpuidle_curr_governor;
			if (cpuidle_switch_governor(gov) < 0)
				cpuidle_prev_governor = NULL;
		}
		mutex_unlock(&cpuidle_lock);
	}

	return ret;
}
EXPORT_SYMBOL_GPL(cpuidle_register_driver);

/**
 * cpuidle_unregister_driver - unregisters a driver
 * @drv: a pointer to a valid struct cpuidle_driver
 *
 * Unregisters the cpuidle driver under a lock to prevent concurrent attempts
 * to [un]register the driver from occuring at the same time.  @drv has to
 * match the currently registered driver.
 */
void cpuidle_unregister_driver(struct cpuidle_driver *drv)
{
	bool enabled = (cpuidle_get_driver() == drv);

	spin_lock(&cpuidle_driver_lock);
	__cpuidle_unregister_driver(drv);
	spin_unlock(&cpuidle_driver_lock);

	if (!enabled)
		return;

	mutex_lock(&cpuidle_lock);
	if (cpuidle_prev_governor) {
		if (!cpuidle_switch_governor(cpuidle_prev_governor))
			cpuidle_prev_governor = NULL;
	}
	mutex_unlock(&cpuidle_lock);
}
EXPORT_SYMBOL_GPL(cpuidle_unregister_driver);

/**
 * cpuidle_get_driver - return the driver tied to the current CPU.
 *
 * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered.
 */
struct cpuidle_driver *cpuidle_get_driver(void)
{
	struct cpuidle_driver *drv;
	int cpu;

	cpu = get_cpu();
	drv = __cpuidle_get_cpu_driver(cpu);
	put_cpu();

	return drv;
}
EXPORT_SYMBOL_GPL(cpuidle_get_driver);

/**
 * cpuidle_get_cpu_driver - return the driver registered for a CPU.
 * @dev: a valid pointer to a struct cpuidle_device
 *
 * Returns a struct cpuidle_driver pointer, or NULL if no driver is registered
 * for the CPU associated with @dev.
 */
struct cpuidle_driver *cpuidle_get_cpu_driver(struct cpuidle_device *dev)
{
	if (!dev)
		return NULL;

	return __cpuidle_get_cpu_driver(dev->cpu);
}
EXPORT_SYMBOL_GPL(cpuidle_get_cpu_driver);

/**
 * cpuidle_driver_ref - get a reference to the driver.
 *
 * Increment the reference counter of the cpuidle driver associated with
 * the current CPU.
 *
 * Returns a pointer to the driver, or NULL if the current CPU has no driver.
 */
struct cpuidle_driver *cpuidle_driver_ref(void)
{
	struct cpuidle_driver *drv;

	spin_lock(&cpuidle_driver_lock);

	drv = cpuidle_get_driver();
	if (drv)
		drv->refcnt++;

	spin_unlock(&cpuidle_driver_lock);
	return drv;
}

/**
 * cpuidle_driver_unref - puts down the refcount for the driver
 *
 * Decrement the reference counter of the cpuidle driver associated with
 * the current CPU.
 */
void cpuidle_driver_unref(void)
{
	struct cpuidle_driver *drv;

	spin_lock(&cpuidle_driver_lock);

	drv = cpuidle_get_driver();
	if (drv && !WARN_ON(drv->refcnt <= 0))
		drv->refcnt--;

	spin_unlock(&cpuidle_driver_lock);
}