Message-Id: <201006200005.35771.rjw@sisk.pl>
Date:	Sun, 20 Jun 2010 00:05:35 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	linux-pm@...ts.linux-foundation.org
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Neil Brown <neilb@...e.de>, mark gross <640e9920@...il.com>
Subject: [RFC][PATCH] PM: Avoid losing wakeup events during suspend

Hi,

One of the arguments during the suspend blockers discussion was that the
mainline kernel didn't contain any mechanisms allowing it to avoid losing
wakeup events during system suspend.

Generally, there are two problems in that area.  First, if a wakeup event
occurs exactly at the same time when /sys/power/state is being written to,
the even may be delivered to user space right before the freezing of it,
in which case 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 and that event is not a wakeup interrupt, the kernel will
not react to it and the system will be suspended.

The following patch illustrates my idea of how these two problems may be
addressed.  It introduces a new global sysfs attribute,
/sys/power/wakeup_count, associated with a running counter of wakeup events
and a helper function, pm_wakeup_event(), that may be used by kernel subsystems
to increment the wakeup events counter.

/sys/power/wakeup_count may be read from or written to by user space.  Reads
will always succeed 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 compare the saved number with the current value of the counter at certain
points of the subsequent suspend (or hibernate) sequence.  If the two values
don't match, the suspend will be aborted just as though a wakeup interrupt
happened.  Reading from /sys/power/wakeup_count again will turn that mechanism
off.

The assumption is that there's a user space power manager that will first
read from /sys/power/wakeup_count.  Then it will check all user space consumers
of wakeup events known to it for unprocessed events.  If there are any, it will
wait for them to be processed and repeat.  In turn, if there are not any,
it will try to write to /sys/power/wakeup_count and if the write is successful,
it will write to /sys/power/state to start suspend, so if any wakeup events
accur past that point, they will be noticed by the kernel and will eventually
cause the suspend to be aborted.

In addition to the above, the patch adds a wakeup events counter to the
power member of struct device and makes 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(), I added it to the
PCI runtime PM wakeup-handling code.

At the moment the patch only contains code changes (ie. no documentation),
but I'm going to add comments etc. if people like the idea.

Please tell me what you think.

Rafael

---
 drivers/base/power/Makefile     |    2 -
 drivers/base/power/main.c       |    1 
 drivers/base/power/power.h      |    3 +
 drivers/base/power/sysfs.c      |    9 ++++
 drivers/base/power/wakeup.c     |   74 ++++++++++++++++++++++++++++++++++++++++
 drivers/pci/pci-acpi.c          |    2 +
 drivers/pci/pcie/pme/pcie_pme.c |    2 +
 include/linux/pm.h              |    6 +++
 kernel/power/hibernate.c        |   14 ++++---
 kernel/power/main.c             |   24 ++++++++++++
 kernel/power/power.h            |    6 +++
 kernel/power/suspend.c          |    2 -
 12 files changed, 138 insertions(+), 7 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 +204,28 @@ static ssize_t state_store(struct kobjec
 
 power_attr(state);
 
+static ssize_t wakeup_count_show(struct kobject *kobj,
+				struct kobj_attribute *attr,
+				char *buf)
+{
+	return sprintf(buf, "%lu\n", pm_get_wakeup_count());
+}
+
+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 +258,7 @@ 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
@@ -266,6 +289,7 @@ static int __init pm_init(void)
 	int error = pm_start_workqueue();
 	if (error)
 		return error;
+	pm_wakeup_events_init();
 	power_kobj = kobject_create_and_add("power", NULL);
 	if (!power_kobj)
 		return -ENOMEM;
Index: linux-2.6/drivers/base/power/wakeup.c
===================================================================
--- /dev/null
+++ linux-2.6/drivers/base/power/wakeup.c
@@ -0,0 +1,74 @@
+
+#include <linux/device.h>
+#include <linux/pm.h>
+
+static unsigned long event_count;
+static unsigned long saved_event_count;
+static bool events_check_enabled;
+static spinlock_t events_lock;
+
+void pm_wakeup_events_init(void)
+{
+	spin_lock_init(&events_lock);
+}
+
+void pm_wakeup_event(struct device *dev)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&events_lock, flags);
+	event_count++;
+	if (dev)
+		dev->power.wakeup_count++;
+	spin_unlock_irqrestore(&events_lock, flags);
+}
+
+bool pm_check_wakeup_events(bool enable)
+{
+	unsigned long flags;
+	bool ret;
+
+	spin_lock_irqsave(&events_lock, flags);
+	ret = !events_check_enabled || (event_count == saved_event_count);
+	events_check_enabled = enable;
+	spin_unlock_irqrestore(&events_lock, flags);
+	return ret;
+}
+
+unsigned long pm_get_wakeup_count(void)
+{
+	unsigned long flags;
+	unsigned long count;
+
+	spin_lock_irqsave(&events_lock, flags);
+	events_check_enabled = false;
+	count = event_count;
+	spin_unlock_irqrestore(&events_lock, flags);
+	return count;
+}
+
+bool pm_save_wakeup_count(unsigned long count)
+{
+	unsigned long flags;
+	bool ret = false;
+
+	spin_lock_irqsave(&events_lock, flags);
+	if (count == event_count) {
+		saved_event_count = count;
+		events_check_enabled = true;
+		ret = true;
+	}
+	spin_unlock_irqrestore(&events_lock, flags);
+	return ret;
+}
+
+unsigned long pm_dev_wakeup_count(struct device *dev)
+{
+	unsigned long flags;
+	unsigned long count;
+
+	spin_lock_irqsave(&events_lock, flags);
+	count = dev->power.wakeup_count;
+	spin_unlock_irqrestore(&events_lock, flags);
+	return count;
+}
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 +553,9 @@ 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);
 #else /* !CONFIG_PM_SLEEP */
 
 #define device_pm_lock() do {} while (0)
@@ -565,6 +569,8 @@ 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) {}
 #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/power.h
===================================================================
--- linux-2.6.orig/kernel/power/power.h
+++ linux-2.6/kernel/power/power.h
@@ -184,6 +184,12 @@ static inline void suspend_test_finish(c
 #ifdef CONFIG_PM_SLEEP
 /* kernel/power/main.c */
 extern int pm_notifier_call_chain(unsigned long val);
+
+/* drivers/base/power/wakeup.c */
+extern void pm_wakeup_events_init(void);
+extern bool pm_check_wakeup_events(bool enable);
+extern unsigned long pm_get_wakeup_count(void);
+extern bool pm_save_wakeup_count(unsigned long count);
 #endif
 
 #ifdef CONFIG_HIGHMEM
Index: linux-2.6/kernel/power/suspend.c
===================================================================
--- linux-2.6.orig/kernel/power/suspend.c
+++ linux-2.6/kernel/power/suspend.c
@@ -157,7 +157,7 @@ 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(false))
 			error = suspend_ops->enter(state);
 		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(true))
 		goto Power_up;
 
 	in_suspend = 1;
@@ -511,14 +511,18 @@ int hibernation_platform_enter(void)
 
 	local_irq_disable();
 	sysdev_suspend(PMSG_HIBERNATE);
+	if (!pm_check_wakeup_events(false))
+		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 +48,8 @@ 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);
+		if (device_may_wakeup(&pci_dev->dev))
+			pm_wakeup_event(&pci_dev->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
@@ -147,6 +147,8 @@ 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);
+			if (device_may_wakeup(&dev->dev))
+				pm_wakeup_event(&dev->dev);
 			ret = true;
 		}
 
Index: linux-2.6/drivers/base/power/power.h
===================================================================
--- linux-2.6.orig/drivers/base/power/power.h
+++ linux-2.6/drivers/base/power/power.h
@@ -30,6 +30,9 @@ extern void device_pm_move_before(struct
 extern void device_pm_move_after(struct device *, struct device *);
 extern void device_pm_move_last(struct device *);
 
+/* drivers/base/power/wakeup.c */
+extern unsigned long pm_dev_wakeup_count(struct device *dev);
+
 #else /* !CONFIG_PM_SLEEP */
 
 static inline void device_pm_init(struct device *dev)
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
@@ -144,6 +144,14 @@ 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", pm_dev_wakeup_count(dev));
+}
+
+static DEVICE_ATTR(wakeup_count, 0444, wakeup_count_show, NULL);
+
 #ifdef CONFIG_PM_ADVANCED_DEBUG
 #ifdef CONFIG_PM_RUNTIME
 
@@ -230,6 +238,7 @@ 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

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