Message-ID: <20100627222804.GA5522@gvim.org>
Date:	Sun, 27 Jun 2010 15:28:05 -0700
From:	mark gross <640e9920@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-pm@...ts.linux-foundation.org,
	Alan Stern <stern@...land.harvard.edu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Neil Brown <neilb@...e.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	mark gross <640e9920@...il.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Florian Mickler <florian@...kler.org>,
	linux-pci@...r.kernel.org, Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH] PM: Make it possible to avoid wakeup events from being
 lost

Looks good to me!

--mgross

On Sat, Jun 26, 2010 at 03:14:13PM +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rjw@...k.pl>
> 
> One of the arguments during the suspend blockers discussion was that
> the mainline kernel didn't contain any mechanisms making it possible
> to avoid losing wakeup events during system suspend.
> 
> Generally, there are two problems in that area.  First, if a wakeup
> event occurs exactly when /sys/power/state is being written to, it
> may be delivered to user space right before the freezer kicks in, so
> the user space consumer of the event may not be able to process it
> before the system is suspended.  Second, if a wakeup event occurs
> after user space has been frozen, it is not generally guaranteed that
> the ongoing transition of the system into a sleep state will be
> aborted.
> 
> To address these issues introduce a new global sysfs attribute,
> /sys/power/wakeup_count, associated with a running counter of wakeup
> events and three helper functions, pm_stay_awake(), pm_relax(), and
> pm_wakeup_event(), that may be used by kernel subsystems to control
> the behavior of this attribute and to request the PM core to abort
> system transitions into a sleep state already in progress.
> 
> The /sys/power/wakeup_count file may be read from or written to by
> user space.  Reads will always succeed (unless interrupted by a
> signal) and return the current value of the wakeup events counter.
> Writes, however, will only succeed if the written number is equal to
> the current value of the wakeup events counter.  If a write is
> successful, it will cause the kernel to save the current value of the
> wakeup events counter and to abort the subsequent system transition
> into a sleep state if any wakeup events are reported after the write
> has returned.
> 
> [The assumption is that before writing to /sys/power/state user space
> will first read from /sys/power/wakeup_count.  Next, user space
> consumers of wakeup events will have a chance to acknowledge or
> veto the upcoming system transition to a sleep state.  Finally, if
> the transition is allowed to proceed, /sys/power/wakeup_count will
> be written to and if that succeeds, /sys/power/state will be written
> to as well.  Still, if any wakeup events are reported to the PM core
> by kernel subsystems after that point, the transition will be
> aborted.]
> 
> Additionally, put a wakeup events counter into struct dev_pm_info and
> make these per-device wakeup event counters available via sysfs,
> so that it's possible to check the activity of various wakeup event
> sources within the kernel.
> 
> To illustrate how subsystems can use pm_wakeup_event(), make the
> low-level PCI runtime PM wakeup-handling code use it.
> 
> Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
> ---
>  Documentation/ABI/testing/sysfs-power |   14 +
>  drivers/base/power/Makefile           |    2 
>  drivers/base/power/main.c             |    1 
>  drivers/base/power/sysfs.c            |   11 +
>  drivers/base/power/wakeup.c           |  240 ++++++++++++++++++++++++++++++++++
>  drivers/pci/pci-acpi.c                |    1 
>  drivers/pci/pci.c                     |   20 ++
>  drivers/pci/pci.h                     |    1 
>  drivers/pci/pcie/pme/pcie_pme.c       |    5 
>  include/linux/pm.h                    |   10 +
>  include/linux/suspend.h               |    7 
>  kernel/power/hibernate.c              |   20 +-
>  kernel/power/main.c                   |   53 +++++++
>  kernel/power/suspend.c                |    4 
>  14 files changed, 379 insertions(+), 10 deletions(-)
> 
> Index: linux-2.6/kernel/power/main.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/main.c
> +++ linux-2.6/kernel/power/main.c
> @@ -204,6 +204,58 @@ static ssize_t state_store(struct kobjec
>  
>  power_attr(state);
>  
> +/*
> + * The 'wakeup_count' attribute, along with the functions defined in
> + * drivers/base/power/wakeup.c, provides a means by which wakeup events can be
> + * handled in a non-racy way.
> + *
> + * If a wakeup event occurs when the system is in a sleep state, it simply is
> + * woken up.  In turn, if an event that would wake the system up from a sleep
> + * state occurs when it is undergoing a transition to that sleep state, the
> + * transition should be aborted.  Moreover, if such an event occurs when the
> + * system is in the working state, an attempt to start a transition to the
> + * given sleep state should fail during certain period after the detection of
> + * the event.  Using the 'state' attribute alone is not sufficient to satisfy
> + * these requirements, because a wakeup event may occur exactly when 'state'
> + * is being written to and may be delivered to user space right before it is
> + * frozen, so the event will remain only partially processed until the system is
> + * woken up by another event.  In particular, it won't cause the transition to
> + * a sleep state to be aborted.
> + *
> + * This difficulty may be overcome if user space uses 'wakeup_count' before
> + * writing to 'state'.  It first should read from 'wakeup_count' and store
> + * the read value.  Then, after carrying out its own preparations for the system
> + * transition to a sleep state, it should write the stored value to
> + * 'wakeup_count'.  If that fails, at least one wakeup event has occured since
> + * 'wakeup_count' was read and 'state' should not be written to.  Otherwise, it
> + * is allowed to write to 'state', but the transition will be aborted if there
> + * are any wakeup events detected after 'wakeup_count' was written to.
> + */
> +
> +static ssize_t wakeup_count_show(struct kobject *kobj,
> +				struct kobj_attribute *attr,
> +				char *buf)
> +{
> +	unsigned long val;
> +
> +	return pm_get_wakeup_count(&val) ? sprintf(buf, "%lu\n", val) : -EINTR;
> +}
> +
> +static ssize_t wakeup_count_store(struct kobject *kobj,
> +				struct kobj_attribute *attr,
> +				const char *buf, size_t n)
> +{
> +	unsigned long val;
> +
> +	if (sscanf(buf, "%lu", &val) == 1) {
> +		if (pm_save_wakeup_count(val))
> +			return n;
> +	}
> +	return -EINVAL;
> +}
> +
> +power_attr(wakeup_count);
> +
>  #ifdef CONFIG_PM_TRACE
>  int pm_trace_enabled;
>  
> @@ -236,6 +288,7 @@ static struct attribute * g[] = {
>  #endif
>  #ifdef CONFIG_PM_SLEEP
>  	&pm_async_attr.attr,
> +	&wakeup_count_attr.attr,
>  #ifdef CONFIG_PM_DEBUG
>  	&pm_test_attr.attr,
>  #endif
> Index: linux-2.6/drivers/base/power/wakeup.c
> ===================================================================
> --- /dev/null
> +++ linux-2.6/drivers/base/power/wakeup.c
> @@ -0,0 +1,240 @@
> +/*
> + * drivers/base/power/wakeup.c - System wakeup events framework
> + *
> + * Copyright (c) 2010 Rafael J. Wysocki <rjw@...k.pl>, Novell Inc.
> + *
> + * This file is released under the GPLv2.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/slab.h>
> +#include <linux/sched.h>
> +#include <linux/capability.h>
> +#include <linux/suspend.h>
> +#include <linux/pm.h>
> +
> +/*
> + * If set, the suspend/hibernate code will abort transitions to a sleep state
> + * if wakeup events are registered during or immediately before the transition.
> + */
> +bool events_check_enabled;
> +
> +/* The counter of registered wakeup events. */
> +static unsigned long event_count;
> +/* A preserved old value of event_count. */
> +static unsigned long saved_event_count;
> +/* The counter of wakeup events being processed. */
> +static unsigned long events_in_progress;
> +
> +static DEFINE_SPINLOCK(events_lock);
> +static DECLARE_WAIT_QUEUE_HEAD(events_wait_queue);
> +
> +/*
> + * The functions below use the observation that each wakeup event starts a
> + * period in which the system should not be suspended.  The moment this period
> + * will end depends on how the wakeup event is going to be processed after being
> + * detected and all of the possible cases can be divided into two distinct
> + * groups.
> + *
> + * First, a wakeup event may be detected by the same functional unit that will
> + * carry out the entire processing of it and possibly will pass it to user space
> + * for further processing.  In that case the functional unit that has detected
> + * the event may later "close" the "no suspend" period associated with it
> + * directly as soon as it has been dealt with.  The pair of pm_stay_awake() and
> + * pm_relax(), balanced with each other, is supposed to be used in such
> + * situations.
> + *
> + * Second, a wakeup event may be detected by one functional unit and processed
> + * by another one.  In that case the unit that has detected it cannot really
> + * "close" the "no suspend" period associated with it, unless it knows in
> + * advance what's going to happen to the event during processing.  This
> + * knowledge, however, may not be available to it, so it can simply specify time
> + * to wait before the system can be suspended and pass it as the second
> + * argument of pm_wakeup_event().
> + */
> +
> +/**
> + * pm_stay_awake - Notify the PM core that a wakeup event is being processed.
> + * @dev: Device the wakeup event is related to.
> + *
> + * Notify the PM core of a wakeup event (signaled by @dev) by incrementing the
> + * counter of wakeup events being processed.  If @dev is not NULL, the counter
> + * of wakeup events related to @dev is incremented too.
> + *
> + * Call this function after detecting of a wakeup event if pm_relax() is going
> + * to be called directly after processing the event (and possibly passing it to
> + * user space for further processing).
> + *
> + * It is safe to call this function from interrupt context.
> + */
> +void pm_stay_awake(struct device *dev)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&events_lock, flags);
> +	if (dev)
> +		dev->power.wakeup_count++;
> +
> +	events_in_progress++;
> +	spin_unlock_irqrestore(&events_lock, flags);
> +}
> +
> +/**
> + * pm_relax - Notify the PM core that processing of a wakeup event has ended.
> + *
> + * Notify the PM core that a wakeup event has been processed by decrementing
> + * the counter of wakeup events being processed and incrementing the counter
> + * of registered wakeup events.
> + *
> + * Call this function for wakeup events whose processing started with calling
> + * pm_stay_awake().
> + *
> + * It is safe to call it from interrupt context.
> + */
> +void pm_relax(void)
> +{
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&events_lock, flags);
> +	if (events_in_progress) {
> +		event_count++;
> +		if (!--events_in_progress)
> +			wake_up_all(&events_wait_queue);
> +	}
> +	spin_unlock_irqrestore(&events_lock, flags);
> +}
> +
> +/**
> + * pm_wakeup_work_fn - Deferred closing of a wakeup event.
> + *
> + * Execute pm_relax() for a wakeup event detected in the past and free the
> + * work item object used for queuing up the work.
> + */
> +static void pm_wakeup_work_fn(struct work_struct *work)
> +{
> +	struct delayed_work *dwork = to_delayed_work(work);
> +
> +	pm_relax();
> +	kfree(dwork);
> +}
> +
> +/**
> + * pm_wakeup_event - Notify the PM core of a wakeup event.
> + * @dev: Device the wakeup event is related to.
> + * @msec: Anticipated event processing time (in milliseconds).
> + *
> + * Notify the PM core of a wakeup event (signaled by @dev) that will take
> + * approximately @msec milliseconds to be processed by the kernel.  Increment
> + * the counter of wakeup events being processed and queue up a work item
> + * that will execute pm_relax() for the event after @msec milliseconds.  If @dev
> + * is not NULL, the counter of wakeup events related to @dev is incremented too.
> + *
> + * It is safe to call this function from interrupt context.
> + */
> +void pm_wakeup_event(struct device *dev, unsigned int msec)
> +{
> +	unsigned long flags;
> +	struct delayed_work *dwork;
> +
> +	dwork = msec ? kzalloc(sizeof(*dwork), GFP_ATOMIC) : NULL;
> +
> +	spin_lock_irqsave(&events_lock, flags);
> +	if (dev)
> +		dev->power.wakeup_count++;
> +
> +	if (dwork) {
> +		INIT_DELAYED_WORK(dwork, pm_wakeup_work_fn);
> +		schedule_delayed_work(dwork, msecs_to_jiffies(msec));
> +
> +		events_in_progress++;
> +	} else {
> +		event_count++;
> +	}
> +	spin_unlock_irqrestore(&events_lock, flags);
> +}
> +
> +/**
> + * pm_check_wakeup_events - Check for new wakeup events.
> + *
> + * Compare the current number of registered wakeup events with its preserved
> + * value from the past to check if new wakeup events have been registered since
> + * the old value was stored.  Check if the current number of wakeup events being
> + * processed is zero.
> + */
> +bool pm_check_wakeup_events(void)
> +{
> +	unsigned long flags;
> +	bool ret = true;
> +
> +	spin_lock_irqsave(&events_lock, flags);
> +	if (events_check_enabled) {
> +		ret = (event_count == saved_event_count) && !events_in_progress;
> +		events_check_enabled = ret;
> +	}
> +	spin_unlock_irqrestore(&events_lock, flags);
> +	return ret;
> +}
> +
> +/**
> + * pm_get_wakeup_count - Read the number of registered wakeup events.
> + * @count: Address to store the value at.
> + *
> + * Store the number of registered wakeup events at the address in @count.  Block
> + * if the current number of wakeup events being processed is nonzero.
> + *
> + * Return false if the wait for the number of wakeup events being processed to
> + * drop down to zero has been interrupted by a signal (and the current number
> + * of wakeup events being processed is still nonzero).  Otherwise return true.
> + */
> +bool pm_get_wakeup_count(unsigned long *count)
> +{
> +	bool ret;
> +
> +	spin_lock_irq(&events_lock);
> +	if (capable(CAP_SYS_ADMIN))
> +		events_check_enabled = false;
> +
> +	if (events_in_progress) {
> +		DEFINE_WAIT(wait);
> +
> +		do {
> +			prepare_to_wait(&events_wait_queue, &wait,
> +					TASK_INTERRUPTIBLE);
> +			if (!events_in_progress)
> +				break;
> +			spin_unlock_irq(&events_lock);
> +
> +			schedule();
> +
> +			spin_lock_irq(&events_lock);
> +		} while (!signal_pending(current));
> +		finish_wait(&events_wait_queue, &wait);
> +	}
> +	*count = event_count;
> +	ret = !events_in_progress;
> +	spin_unlock_irq(&events_lock);
> +	return ret;
> +}
> +
> +/**
> + * pm_save_wakeup_count - Save the current number of registered wakeup events.
> + * @count: Value to compare with the current number of registered wakeup events.
> + *
> + * If @count is equal to the current number of registered wakeup events and the
> + * current number of wakeup events being processed is zero, store @count as the
> + * old number of registered wakeup events to be used by pm_check_wakeup_events()
> + * and return true.  Otherwise return false.
> + */
> +bool pm_save_wakeup_count(unsigned long count)
> +{
> +	bool ret = false;
> +
> +	spin_lock_irq(&events_lock);
> +	if (count == event_count && !events_in_progress) {
> +		saved_event_count = count;
> +		events_check_enabled = true;
> +		ret = true;
> +	}
> +	spin_unlock_irq(&events_lock);
> +	return ret;
> +}
> Index: linux-2.6/include/linux/pm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/pm.h
> +++ linux-2.6/include/linux/pm.h
> @@ -457,6 +457,7 @@ struct dev_pm_info {
>  #ifdef CONFIG_PM_SLEEP
>  	struct list_head	entry;
>  	struct completion	completion;
> +	unsigned long		wakeup_count;
>  #endif
>  #ifdef CONFIG_PM_RUNTIME
>  	struct timer_list	suspend_timer;
> @@ -552,6 +553,11 @@ extern void __suspend_report_result(cons
>  	} while (0)
>  
>  extern void device_pm_wait_for_dev(struct device *sub, struct device *dev);
> +
> +/* drivers/base/power/wakeup.c */
> +extern void pm_wakeup_event(struct device *dev, unsigned int msec);
> +extern void pm_stay_awake(struct device *dev);
> +extern void pm_relax(void);
>  #else /* !CONFIG_PM_SLEEP */
>  
>  #define device_pm_lock() do {} while (0)
> @@ -565,6 +571,10 @@ static inline int dpm_suspend_start(pm_m
>  #define suspend_report_result(fn, ret)		do {} while (0)
>  
>  static inline void device_pm_wait_for_dev(struct device *a, struct device *b) {}
> +
> +static inline void pm_wakeup_event(struct device *dev, unsigned int msec) {}
> +static inline void pm_stay_awake(struct device *dev) {}
> +static inline void pm_relax(void) {}
>  #endif /* !CONFIG_PM_SLEEP */
>  
>  /* How to reorder dpm_list after device_move() */
> Index: linux-2.6/drivers/base/power/Makefile
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/Makefile
> +++ linux-2.6/drivers/base/power/Makefile
> @@ -1,5 +1,5 @@
>  obj-$(CONFIG_PM)	+= sysfs.o
> -obj-$(CONFIG_PM_SLEEP)	+= main.o
> +obj-$(CONFIG_PM_SLEEP)	+= main.o wakeup.o
>  obj-$(CONFIG_PM_RUNTIME)	+= runtime.o
>  obj-$(CONFIG_PM_OPS)	+= generic_ops.o
>  obj-$(CONFIG_PM_TRACE_RTC)	+= trace.o
> Index: linux-2.6/drivers/base/power/main.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/main.c
> +++ linux-2.6/drivers/base/power/main.c
> @@ -59,6 +59,7 @@ void device_pm_init(struct device *dev)
>  {
>  	dev->power.status = DPM_ON;
>  	init_completion(&dev->power.completion);
> +	dev->power.wakeup_count = 0;
>  	pm_runtime_init(dev);
>  }
>  
> Index: linux-2.6/kernel/power/suspend.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/suspend.c
> +++ linux-2.6/kernel/power/suspend.c
> @@ -172,8 +172,10 @@ static int suspend_enter(suspend_state_t
>  
>  	error = sysdev_suspend(PMSG_SUSPEND);
>  	if (!error) {
> -		if (!suspend_test(TEST_CORE))
> +		if (!suspend_test(TEST_CORE) && pm_check_wakeup_events()) {
>  			error = suspend_ops->enter(state);
> +			events_check_enabled = false;
> +		}
>  		sysdev_resume();
>  	}
>  
> Index: linux-2.6/kernel/power/hibernate.c
> ===================================================================
> --- linux-2.6.orig/kernel/power/hibernate.c
> +++ linux-2.6/kernel/power/hibernate.c
> @@ -277,7 +277,7 @@ static int create_image(int platform_mod
>  		goto Enable_irqs;
>  	}
>  
> -	if (hibernation_test(TEST_CORE))
> +	if (hibernation_test(TEST_CORE) || !pm_check_wakeup_events())
>  		goto Power_up;
>  
>  	in_suspend = 1;
> @@ -288,8 +288,10 @@ static int create_image(int platform_mod
>  			error);
>  	/* Restore control flow magically appears here */
>  	restore_processor_state();
> -	if (!in_suspend)
> +	if (!in_suspend) {
> +		events_check_enabled = false;
>  		platform_leave(platform_mode);
> +	}
>  
>   Power_up:
>  	sysdev_resume();
> @@ -511,14 +513,20 @@ int hibernation_platform_enter(void)
>  
>  	local_irq_disable();
>  	sysdev_suspend(PMSG_HIBERNATE);
> +	if (!pm_check_wakeup_events()) {
> +		error = -EAGAIN;
> +		goto Power_up;
> +	}
> +
>  	hibernation_ops->enter();
>  	/* We should never get here */
>  	while (1);
>  
> -	/*
> -	 * We don't need to reenable the nonboot CPUs or resume consoles, since
> -	 * the system is going to be halted anyway.
> -	 */
> + Power_up:
> +	sysdev_resume();
> +	local_irq_enable();
> +	enable_nonboot_cpus();
> +
>   Platform_finish:
>  	hibernation_ops->finish();
>  
> Index: linux-2.6/drivers/pci/pci-acpi.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pci-acpi.c
> +++ linux-2.6/drivers/pci/pci-acpi.c
> @@ -48,6 +48,7 @@ static void pci_acpi_wake_dev(acpi_handl
>  	if (event == ACPI_NOTIFY_DEVICE_WAKE && pci_dev) {
>  		pci_check_pme_status(pci_dev);
>  		pm_runtime_resume(&pci_dev->dev);
> +		pci_wakeup_event(pci_dev);
>  		if (pci_dev->subordinate)
>  			pci_pme_wakeup_bus(pci_dev->subordinate);
>  	}
> Index: linux-2.6/drivers/pci/pcie/pme/pcie_pme.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pcie/pme/pcie_pme.c
> +++ linux-2.6/drivers/pci/pcie/pme/pcie_pme.c
> @@ -154,6 +154,7 @@ static bool pcie_pme_walk_bus(struct pci
>  		/* Skip PCIe devices in case we started from a root port. */
>  		if (!pci_is_pcie(dev) && pci_check_pme_status(dev)) {
>  			pm_request_resume(&dev->dev);
> +			pci_wakeup_event(dev);
>  			ret = true;
>  		}
>  
> @@ -254,8 +255,10 @@ static void pcie_pme_handle_request(stru
>  	if (found) {
>  		/* The device is there, but we have to check its PME status. */
>  		found = pci_check_pme_status(dev);
> -		if (found)
> +		if (found) {
>  			pm_request_resume(&dev->dev);
> +			pci_wakeup_event(dev);
> +		}
>  		pci_dev_put(dev);
>  	} else if (devfn) {
>  		/*
> Index: linux-2.6/drivers/base/power/sysfs.c
> ===================================================================
> --- linux-2.6.orig/drivers/base/power/sysfs.c
> +++ linux-2.6/drivers/base/power/sysfs.c
> @@ -73,6 +73,8 @@
>   *	device are known to the PM core.  However, for some devices this
>   *	attribute is set to "enabled" by bus type code or device drivers and in
>   *	that cases it should be safe to leave the default value.
> + *
> + *	wakeup_count - Report the number of wakeup events related to the device
>   */
>  
>  static const char enabled[] = "enabled";
> @@ -144,6 +146,14 @@ wake_store(struct device * dev, struct d
>  
>  static DEVICE_ATTR(wakeup, 0644, wake_show, wake_store);
>  
> +static ssize_t wakeup_count_show(struct device *dev,
> +				struct device_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%lu\n", dev->power.wakeup_count);
> +}
> +
> +static DEVICE_ATTR(wakeup_count, 0444, wakeup_count_show, NULL);
> +
>  #ifdef CONFIG_PM_ADVANCED_DEBUG
>  #ifdef CONFIG_PM_RUNTIME
>  
> @@ -230,6 +240,7 @@ static struct attribute * power_attrs[] 
>  	&dev_attr_control.attr,
>  #endif
>  	&dev_attr_wakeup.attr,
> +	&dev_attr_wakeup_count.attr,
>  #ifdef CONFIG_PM_ADVANCED_DEBUG
>  	&dev_attr_async.attr,
>  #ifdef CONFIG_PM_RUNTIME
> Index: linux-2.6/drivers/pci/pci.h
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pci.h
> +++ linux-2.6/drivers/pci/pci.h
> @@ -56,6 +56,7 @@ extern void pci_update_current_state(str
>  extern void pci_disable_enabled_device(struct pci_dev *dev);
>  extern bool pci_check_pme_status(struct pci_dev *dev);
>  extern int pci_finish_runtime_suspend(struct pci_dev *dev);
> +extern void pci_wakeup_event(struct pci_dev *dev);
>  extern int __pci_pme_wakeup(struct pci_dev *dev, void *ign);
>  extern void pci_pme_wakeup_bus(struct pci_bus *bus);
>  extern void pci_pm_init(struct pci_dev *dev);
> Index: linux-2.6/drivers/pci/pci.c
> ===================================================================
> --- linux-2.6.orig/drivers/pci/pci.c
> +++ linux-2.6/drivers/pci/pci.c
> @@ -1275,6 +1275,22 @@ bool pci_check_pme_status(struct pci_dev
>  	return ret;
>  }
>  
> +/*
> + * Time to wait before the system can be put into a sleep state after reporting
> + * a wakeup event signaled by a PCI device.
> + */
> +#define PCI_WAKEUP_COOLDOWN	100
> +
> +/**
> + * pci_wakeup_event - Report a wakeup event related to a given PCI device.
> + * @dev: Device to report the wakeup event for.
> + */
> +void pci_wakeup_event(struct pci_dev *dev)
> +{
> +	if (device_may_wakeup(&dev->dev))
> +		pm_wakeup_event(&dev->dev, PCI_WAKEUP_COOLDOWN);
> +}
> +
>  /**
>   * pci_pme_wakeup - Wake up a PCI device if its PME Status bit is set.
>   * @dev: Device to handle.
> @@ -1285,8 +1301,10 @@ bool pci_check_pme_status(struct pci_dev
>   */
>  static int pci_pme_wakeup(struct pci_dev *dev, void *ign)
>  {
> -	if (pci_check_pme_status(dev))
> +	if (pci_check_pme_status(dev)) {
>  		pm_request_resume(&dev->dev);
> +		pci_wakeup_event(dev);
> +	}
>  	return 0;
>  }
>  
> Index: linux-2.6/include/linux/suspend.h
> ===================================================================
> --- linux-2.6.orig/include/linux/suspend.h
> +++ linux-2.6/include/linux/suspend.h
> @@ -295,6 +295,13 @@ extern int unregister_pm_notifier(struct
>  		{ .notifier_call = fn, .priority = pri };	\
>  	register_pm_notifier(&fn##_nb);			\
>  }
> +
> +/* drivers/base/power/wakeup.c */
> +extern bool events_check_enabled;
> +
> +extern bool pm_check_wakeup_events(void);
> +extern bool pm_get_wakeup_count(unsigned long *count);
> +extern bool pm_save_wakeup_count(unsigned long count);
>  #else /* !CONFIG_PM_SLEEP */
>  
>  static inline int register_pm_notifier(struct notifier_block *nb)
> Index: linux-2.6/Documentation/ABI/testing/sysfs-power
> ===================================================================
> --- linux-2.6.orig/Documentation/ABI/testing/sysfs-power
> +++ linux-2.6/Documentation/ABI/testing/sysfs-power
> @@ -114,3 +114,17 @@ Description:
>  		if this file contains "1", which is the default.  It may be
>  		disabled by writing "0" to this file, in which case all devices
>  		will be suspended and resumed synchronously.
> +
> +What:		/sys/power/wakeup_count
> +Date:		July 2010
> +Contact:	Rafael J. Wysocki <rjw@...k.pl>
> +Description:
> +		The /sys/power/wakeup_count file allows user space to avoid
> +		losing wakeup events when transitioning the system into a sleep
> +		state.  Reading from it returns the current number of registered
> +		wakeup events and it blocks if some wakeup events are being
> +		processed at the time the file is read from.  Writing to it
> +		will only succeed if the current number of wakeup events is
> +		equal to the written value and, if successful, will make the
> +		kernel abort a subsequent transition to a sleep state if any
> +		wakeup events are reported after the write has returned.
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