[PATCH] PM: Introduce core framework for run-time PM of I/O devices

[Rafael J. Wysocki]

Hi,

Below is the current version of my "run-time PM for I/O devices" patch.

I've done my best to address the comments received during the recent
discussions, but at the same time I've tried to make the patch only contain
the most essential things.  For this reason, for example, the sysfs interface
is not there and it's going to be added in a separate patch.

Please let me know if you want me to change anything in this patch or to add
anything new to it.  [Magnus, I remember you wanted something like
->runtime_wakeup() along with ->runtime_idle(), but I'm not sure it's really
necessary.  Please let me know if you have any particular usage scenario for
it.]

Best,
Rafael

---
From: Rafael J. Wysocki <rjw@xxxxxxx>

Introduce a core framework for run-time power management of I/O
devices.  Add device run-time PM fields to 'struct dev_pm_info'
and device run-time PM callbacks to 'struct dev_pm_ops'.  Introduce
a run-time PM workqueue and define some device run-time PM helper
functions at the core level.  Document all these things.

Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
---
 Documentation/power/runtime_pm.txt |  250 ++++++++++++++++++++
 drivers/base/dd.c                  |    9 
 drivers/base/power/Makefile        |    1 
 drivers/base/power/main.c          |    5 
 drivers/base/power/runtime.c       |  461 +++++++++++++++++++++++++++++++++++++
 include/linux/pm.h                 |   98 +++++++
 include/linux/pm_runtime.h         |   63 +++++
 kernel/power/Kconfig               |   14 +
 kernel/power/main.c                |   17 +
 9 files changed, 915 insertions(+), 3 deletions(-)

Index: linux-2.6/kernel/power/Kconfig
===================================================================
--- linux-2.6.orig/kernel/power/Kconfig
+++ linux-2.6/kernel/power/Kconfig
@@ -208,3 +208,17 @@ config APM_EMULATION
 	  random kernel OOPSes or reboots that don't seem to be related to
 	  anything, try disabling/enabling this option (or disabling/enabling
 	  APM in your BIOS).
+
+config PM_RUNTIME
+	bool "Run-time PM core functionality"
+	depends on PM
+	---help---
+	  Enable functionality allowing I/O devices to be put into energy-saving
+	  (low power) states at run time (or autosuspended) after a specified
+	  period of inactivity and woken up in response to a hardware-generated
+	  wake-up event or a driver's request.
+
+	  Hardware support is generally required for this functionality to work
+	  and the bus type drivers of the buses the devices are on are
+	  responsibile for the actual handling of the autosuspend requests and
+	  wake-up events.
Index: linux-2.6/kernel/power/main.c
===================================================================
--- linux-2.6.orig/kernel/power/main.c
+++ linux-2.6/kernel/power/main.c
@@ -11,6 +11,7 @@
 #include <linux/kobject.h>
 #include <linux/string.h>
 #include <linux/resume-trace.h>
+#include <linux/workqueue.h>
 
 #include "power.h"
 
@@ -217,8 +218,24 @@ static struct attribute_group attr_group
 	.attrs = g,
 };
 
+#ifdef CONFIG_PM_RUNTIME
+struct workqueue_struct *pm_wq;
+
+static int __init pm_start_workqueue(void)
+{
+	pm_wq = create_freezeable_workqueue("pm");
+
+	return pm_wq ? 0 : -ENOMEM;
+}
+#else
+static inline int pm_start_workqueue(void) { return 0; }
+#endif
+
 static int __init pm_init(void)
 {
+	int error = pm_start_workqueue();
+	if (error)
+		return error;
 	power_kobj = kobject_create_and_add("power", NULL);
 	if (!power_kobj)
 		return -ENOMEM;
Index: linux-2.6/include/linux/pm.h
===================================================================
--- linux-2.6.orig/include/linux/pm.h
+++ linux-2.6/include/linux/pm.h
@@ -22,6 +22,9 @@
 #define _LINUX_PM_H
 
 #include <linux/list.h>
+#include <linux/workqueue.h>
+#include <linux/spinlock.h>
+#include <linux/completion.h>
 
 /*
  * Callbacks for platform drivers to implement.
@@ -165,6 +168,26 @@ typedef struct pm_message {
  * It is allowed to unregister devices while the above callbacks are being
  * executed.  However, it is not allowed to unregister a device from within any
  * of its own callbacks.
+ *
+ * There also are the following callbacks related to run-time power management
+ * of devices:
+ *
+ * @runtime_suspend: Prepare the device for a condition in which it won't be
+ *	able to communicate with the CPU(s) and RAM due to power management.
+ *	This need not mean that the device should be put into a low power state,
+ *	like for example when the device is behind a link, represented by a
+ *	separate device object, that is going to be turned off for power
+ *	management purposes.
+ *
+ * @runtime_resume: Put the device into the fully active state in response to a
+ *	wake-up event generated by hardware or at a request of software.  If
+ *	necessary, put the device into the full power state and restore its
+ *	registers, so that it is fully operational.
+ *
+ * @runtime_idle: Device appears to be inactive and it might be put into a low
+ *	power state if all of the necessary conditions are satisfied.  Check
+ *	these conditions and handle the device as appropriate, possibly queueing
+ *	a suspend request for it.
  */
 
 struct dev_pm_ops {
@@ -182,6 +205,11 @@ struct dev_pm_ops {
 	int (*thaw_noirq)(struct device *dev);
 	int (*poweroff_noirq)(struct device *dev);
 	int (*restore_noirq)(struct device *dev);
+#ifdef CONFIG_PM_RUNTIME
+	int (*runtime_suspend)(struct device *dev);
+	int (*runtime_resume)(struct device *dev);
+	void (*runtime_idle)(struct device *dev);
+#endif
 };
 
 /**
@@ -315,14 +343,78 @@ enum dpm_state {
 	DPM_OFF_IRQ,
 };
 
+/**
+ * Device run-time power management state.
+ *
+ * These state labels are used internally by the PM core to indicate the current
+ * status of a device with respect to the PM core operations.  They do not
+ * reflect the actual power state of the device or its status as seen by the
+ * driver.
+ *
+ * RPM_ACTIVE		Device is fully operational, no run-time PM requests are
+ *			pending for it.
+ *
+ * RPM_IDLE		It has been requested that the device be suspended.
+ *			Suspend request has been put into the run-time PM
+ *			workqueue and it's pending execution.
+ *
+ * RPM_SUSPENDING	Device bus type's ->runtime_suspend() callback is being
+ *			executed.
+ *
+ * RPM_SUSPENDED	Device bus type's ->runtime_suspend() callback has
+ *			completed successfully.  The device is regarded as
+ *			suspended.
+ *
+ * RPM_WAKE		It has been requested that the device be woken up.
+ *			Resume request has been put into the run-time PM
+ *			workqueue and it's pending execution.
+ *
+ * RPM_RESUMING		Device bus type's ->runtime_resume() callback is being
+ *			executed.
+ *
+ * RPM_ERROR		Represents a condition from which the PM core cannot
+ *			recover by itself.  If the device's run-time PM status
+ *			field has this value, all of the run-time PM operations
+ *			carried out for the device by the core will fail, until
+ *			the status field is changed to either RPM_ACTIVE or
+ *			RPM_SUSPENDED (it is not valid to use the other values
+ *			in such a situation) by the device's driver or bus type.
+ *			This happens when the device bus type's
+ *			->runtime_suspend() or ->runtime_resume() callback
+ *			returns error code different from -EAGAIN or -EBUSY.
+ */
+
+#define RPM_ACTIVE	0
+#define RPM_IDLE	0x01
+#define RPM_SUSPENDING	0x02
+#define RPM_SUSPENDED	0x04
+#define RPM_WAKE	0x08
+#define RPM_RESUMING	0x10
+#define RPM_ERROR	(-1)
+
+#define RPM_IN_SUSPEND	(RPM_SUSPENDING | RPM_SUSPENDED)
+#define RPM_INACTIVE	(RPM_IDLE | RPM_IN_SUSPEND)
+#define RPM_NO_SUSPEND	(RPM_WAKE | RPM_RESUMING)
+#define RPM_IN_PROGRESS	(RPM_SUSPENDING | RPM_RESUMING)
+
 struct dev_pm_info {
 	pm_message_t		power_state;
-	unsigned		can_wakeup:1;
-	unsigned		should_wakeup:1;
+	unsigned int		can_wakeup:1;
+	unsigned int		should_wakeup:1;
 	enum dpm_state		status;		/* Owned by the PM core */
-#ifdef	CONFIG_PM_SLEEP
+#ifdef CONFIG_PM_SLEEP
 	struct list_head	entry;
 #endif
+#ifdef CONFIG_PM_RUNTIME
+	struct delayed_work	runtime_work;
+	struct completion	work_done;
+	unsigned int		suspend_skip_children:1;
+	unsigned int		suspend_aborted:1;
+	unsigned int		runtime_status:5;
+	int			runtime_error;
+	atomic_t		depth;
+	spinlock_t		lock;
+#endif
 };
 
 /*
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 +1,6 @@
 obj-$(CONFIG_PM)	+= sysfs.o
 obj-$(CONFIG_PM_SLEEP)	+= main.o
+obj-$(CONFIG_PM_RUNTIME)	+= runtime.o
 obj-$(CONFIG_PM_TRACE_RTC)	+= trace.o
 
 ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG
Index: linux-2.6/drivers/base/power/runtime.c
===================================================================
--- /dev/null
+++ linux-2.6/drivers/base/power/runtime.c
@@ -0,0 +1,461 @@
+/*
+ * drivers/base/power/runtime.c - Helper functions for device run-time PM
+ *
+ * Copyright (c) 2009 Rafael J. Wysocki <rjw@xxxxxxx>, Novell Inc.
+ *
+ * This file is released under the GPLv2.
+ */
+
+#include <linux/pm_runtime.h>
+
+/**
+ * pm_runtime_reset - Clear all of the device run-time PM flags.
+ * @dev: Device object to clear the flags for.
+ */
+static void pm_runtime_reset(struct device *dev)
+{
+	dev->power.suspend_aborted = false;
+	dev->power.runtime_status = RPM_ACTIVE;
+}
+
+/**
+ * pm_device_suspended - Check if given device has been suspended at run time.
+ * @dev: Device to check.
+ * @data: Ignored.
+ *
+ * Returns 0 if the device has been suspended and it hasn't been requested to
+ * resume or -EBUSY otherwise.
+ */
+static int pm_device_suspended(struct device *dev, void *data)
+{
+	return dev->power.runtime_status == RPM_SUSPENDED ? 0 : -EBUSY;
+}
+
+/**
+ * pm_check_children - Check if all children of a device have been suspended.
+ * @dev: Device to check.
+ *
+ * Returns 0 if all children of the device have been suspended or -EBUSY
+ * otherwise.
+ */
+static int pm_check_children(struct device *dev)
+{
+	return dev->power.suspend_skip_children ? 0 :
+			device_for_each_child(dev, NULL, pm_device_suspended);
+}
+
+/**
+ * pm_runtime_notify_idle - Run a device bus type's runtime_idle() callback.
+ * @dev: Device to notify.
+ *
+ * Check if all children of given device are suspended and call the device bus
+ * type's ->runtime_idle() callback if that's the case.
+ */
+static void pm_runtime_notify_idle(struct device *dev)
+{
+	if (atomic_read(&dev->power.depth) > 0 || pm_check_children(dev))
+		return;
+
+	if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_idle)
+		dev->bus->pm->runtime_idle(dev);
+}
+
+/**
+ * pm_runtime_suspend - Run a device bus type's runtime_suspend() callback.
+ * @dev: Device to suspend.
+ *
+ * Check if the status of the device is appropriate and run the
+ * ->runtime_suspend() callback provided by the device's bus type driver.
+ * Update the run-time PM flags in the device object to reflect the current
+ * status of the device.
+ */
+int pm_runtime_suspend(struct device *dev)
+{
+	int error = 0;
+
+	if (atomic_read(&dev->power.depth) > 0)
+		return -EBUSY;
+
+	spin_lock(&dev->power.lock);
+
+	if (dev->power.runtime_status & RPM_SUSPENDED) {
+		goto out;
+	} else if (dev->power.runtime_status & RPM_NO_SUSPEND) {
+		/* Device is resuming or there's a resume request pending. */
+		error = -EAGAIN;
+		goto out;
+	} else if (dev->power.runtime_status == RPM_IDLE
+	    && dev->power.suspend_aborted) {
+		dev->power.suspend_aborted = false;
+		dev->power.runtime_status = RPM_ACTIVE;
+		goto out;
+	} else if (pm_check_children(dev)) {
+		/*
+		 * We can only suspend the device if all of its children have
+		 * been suspended.
+		 */
+		error = -EAGAIN;
+		goto out;
+	} else if (dev->power.runtime_status == RPM_SUSPENDING) {
+		spin_unlock(&dev->power.lock);
+
+		/*
+		 * Another suspend is running in parallel with us.  Wait for it
+		 * to complete and return.
+		 */
+		wait_for_completion(&dev->power.work_done);
+
+		return dev->power.runtime_error;
+	}
+
+	dev->power.runtime_status = RPM_SUSPENDING;
+	init_completion(&dev->power.work_done);
+
+	spin_unlock(&dev->power.lock);
+
+	if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_suspend)
+		error = dev->bus->pm->runtime_suspend(dev);
+
+	spin_lock(&dev->power.lock);
+
+	/*
+	 * Resume request might have been queued in the meantime, in which case
+	 * the RPM_WAKE bit is also set in runtime_status.
+	 */
+	dev->power.runtime_status &= ~RPM_SUSPENDING;
+	switch (error) {
+	case 0:
+		dev->power.runtime_status |= RPM_SUSPENDED;
+		break;
+	case -EAGAIN:
+	case -EBUSY:
+		dev->power.runtime_status = RPM_ACTIVE;
+		break;
+	default:
+		dev->power.runtime_status = RPM_ERROR;
+	}
+	dev->power.runtime_error = error;
+	complete(&dev->power.work_done);
+
+	if (!error && !(dev->power.runtime_status & RPM_WAKE) && dev->parent) {
+		spin_unlock(&dev->power.lock);
+
+		pm_runtime_notify_idle(dev->parent);
+
+		return 0;
+	}
+
+ out:
+	spin_unlock(&dev->power.lock);
+
+	return error;
+}
+EXPORT_SYMBOL_GPL(pm_runtime_suspend);
+
+/**
+ * pm_runtime_suspend_work - Run pm_runtime_suspend() for a device.
+ * @work: Work structure used for scheduling the execution of this function.
+ *
+ * Use @work to get the device object the suspend has been scheduled for and
+ * run pm_runtime_suspend() for it.
+ */
+static void pm_runtime_suspend_work(struct work_struct *work)
+{
+	pm_runtime_suspend(pm_work_to_device(work));
+}
+
+/**
+ * pm_request_suspend - Schedule run-time suspend of given device.
+ * @dev: Device to suspend.
+ * @delay: Time, in jiffies, to wait before attempting to suspend the device.
+ */
+void pm_request_suspend(struct device *dev, unsigned long delay)
+{
+	unsigned long flags;
+
+	if (atomic_read(&dev->power.depth) > 0)
+		return;
+
+	spin_lock_irqsave(&dev->power.lock, flags);
+
+	if (dev->power.runtime_status != RPM_ACTIVE)
+		goto out;
+
+	dev->power.runtime_status = RPM_IDLE;
+	dev->power.suspend_aborted = false;
+	INIT_DELAYED_WORK(&dev->power.runtime_work, pm_runtime_suspend_work);
+	queue_delayed_work(pm_wq, &dev->power.runtime_work, delay);
+
+ out:
+	spin_unlock_irqrestore(&dev->power.lock, flags);
+}
+EXPORT_SYMBOL_GPL(pm_request_suspend);
+
+/**
+ * pm_cancel_suspend - Cancel a pending suspend request for given device.
+ * @dev: Device to cancel the suspend request for.
+ *
+ * Should be called under pm_lock_device() and only if we are sure that the
+ * ->autosuspend() callback hasn't started to yet.
+ */
+static void pm_cancel_suspend(struct device *dev)
+{
+	dev->power.suspend_aborted = true;
+	cancel_delayed_work(&dev->power.runtime_work);
+	dev->power.runtime_status = RPM_ACTIVE;
+}
+
+/**
+ * pm_runtime_resume - Run a device bus type's runtime_resume() callback.
+ * @dev: Device to resume.
+ *
+ * Check if the device is really suspended and run the ->runtime_resume()
+ * callback provided by the device's bus type driver.  Update the run-time PM
+ * flags in the device object to reflect the current status of the device.  If
+ * runtime suspend is in progress while this function is being run, wait for it
+ * to finish before resuming the device.  If runtime suspend is scheduled, but
+ * it hasn't started yet, cancel it and we're done.
+ */
+int pm_runtime_resume(struct device *dev)
+{
+	int error = 0;
+
+ repeat:
+	if (atomic_read(&dev->power.depth) > 0)
+		return -EBUSY;
+
+	if (dev->parent)
+		spin_lock(&dev->parent->power.lock);
+	spin_lock(&dev->power.lock);
+
+	if (dev->power.runtime_status == RPM_ACTIVE) {
+		goto out_unlock;
+	} else if (dev->power.runtime_status == RPM_IDLE) {
+		/* ->runtime_suspend() hasn't started yet, no need to resume. */
+		pm_cancel_suspend(dev);
+		goto out_unlock;
+	}
+
+	if (dev->power.runtime_status & RPM_SUSPENDING) {
+		spin_unlock(&dev->power.lock);
+		if (dev->parent)
+			spin_unlock(&dev->parent->power.lock);
+
+		/*
+		 * A suspend is running in parallel with us.  Wait for it to
+		 * complete and repeat.
+		 */
+		wait_for_completion(&dev->power.work_done);
+
+		goto repeat;
+	} else if (dev->power.runtime_status == RPM_SUSPENDED && dev->parent
+	    && dev->parent->power.runtime_status != RPM_ACTIVE) {
+		spin_unlock(&dev->power.lock);
+		spin_unlock(&dev->parent->power.lock);
+
+		/* The device's parent is not active.  Resume it and repeat. */
+		error = pm_runtime_resume(dev->parent);
+		if (error)
+			return error;
+
+		goto repeat;
+	}
+
+	if (dev->power.runtime_status == RPM_RESUMING) {
+		spin_unlock(&dev->power.lock);
+		if (dev->parent)
+			spin_unlock(&dev->parent->power.lock);
+
+		/*
+		 * There's another resume running in parallel with us. Wait for
+		 * it to complete and return.
+		 */
+		wait_for_completion(&dev->power.work_done);
+
+		return dev->power.runtime_error;
+	}
+
+	dev->power.runtime_status = RPM_RESUMING;
+	init_completion(&dev->power.work_done);
+
+	spin_unlock(&dev->power.lock);
+	if (dev->parent)
+		spin_unlock(&dev->parent->power.lock);
+
+	if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_resume)
+		error = dev->bus->pm->runtime_resume(dev);
+
+	spin_lock(&dev->power.lock);
+
+	switch (error) {
+	case 0:
+		dev->power.runtime_status = RPM_ACTIVE;
+		break;
+	case -EAGAIN:
+	case -EBUSY:
+		dev->power.runtime_status = RPM_SUSPENDED;
+		break;
+	default:
+		dev->power.runtime_status = RPM_ERROR;
+	}
+	dev->power.runtime_error = error;
+	complete(&dev->power.work_done);
+
+ out:
+	spin_unlock(&dev->power.lock);
+
+	return error;
+
+ out_unlock:
+	if (dev->parent)
+		spin_unlock(&dev->parent->power.lock);
+	goto out;
+}
+EXPORT_SYMBOL_GPL(pm_runtime_resume);
+
+/**
+ * pm_runtime_resume_work - Run pm_runtime_resume() for a device.
+ * @work: Work structure used for scheduling the execution of this function.
+ *
+ * Use @work to get the device object the resume has been scheduled for and run
+ * pm_runtime_resume() for it.
+ */
+static void pm_runtime_resume_work(struct work_struct *work)
+{
+	pm_runtime_resume(pm_work_to_device(work));
+}
+
+/**
+ * pm_request_resume - Schedule run-time resume of given device.
+ * @dev: Device to resume.
+ */
+void pm_request_resume(struct device *dev)
+{
+	unsigned long parent_flags = 0, flags;
+
+ repeat:
+	if (atomic_read(&dev->power.depth) > 0)
+		return;
+
+	if (dev->parent)
+		spin_lock_irqsave(&dev->parent->power.lock, parent_flags);
+	spin_lock_irqsave(&dev->power.lock, flags);
+
+	if (dev->power.runtime_status == RPM_IDLE) {
+		/* Autosuspend request is pending, no need to resume. */
+		pm_cancel_suspend(dev);
+		goto out;
+	} else if (!(dev->power.runtime_status & RPM_IN_SUSPEND)) {
+		goto out;
+	} else if (dev->parent
+	    && (dev->parent->power.runtime_status & RPM_INACTIVE)) {
+		spin_unlock_irqrestore(&dev->power.lock, flags);
+		spin_unlock_irqrestore(&dev->parent->power.lock, parent_flags);
+
+		/* We have to resume the parent first. */
+		pm_request_resume(dev->parent);
+
+		goto repeat;
+	}
+
+	/*
+	 * The device may be suspending at the moment and we can't clear the
+	 * RPM_SUSPENDING bit in its runtime_status just yet.
+	 */
+	dev->power.runtime_status |= RPM_WAKE;
+	INIT_WORK(&dev->power.runtime_work.work, pm_runtime_resume_work);
+	queue_work(pm_wq, &dev->power.runtime_work.work);
+
+ out:
+	spin_unlock_irqrestore(&dev->power.lock, flags);
+	if (dev->parent)
+		spin_unlock_irqrestore(&dev->parent->power.lock, parent_flags);
+}
+EXPORT_SYMBOL_GPL(pm_request_resume);
+
+/**
+ * pm_cancel_runtime_suspend - Cancel a pending suspend request for a device.
+ * @dev: Device to handle.
+ *
+ * This routine is only supposed to be called when the run-time PM workqueue is
+ * frozen (i.e. during system-wide suspend or hibernation) when it is guaranteed
+ * that no work items are being executed.
+ */
+void pm_cancel_runtime_suspend(struct device *dev)
+{
+	spin_lock(&dev->power.lock);
+
+	if (dev->power.runtime_status == RPM_IDLE) {
+		cancel_delayed_work(&dev->power.runtime_work);
+		pm_runtime_reset(dev);
+	}
+
+	spin_unlock(&dev->power.lock);
+}
+EXPORT_SYMBOL_GPL(pm_cancel_runtime_suspend);
+
+/**
+ * pm_cancel_runtime_resume - Cancel a pending resume request for a device.
+ * @dev: Device to handle.
+ *
+ * This routine is only supposed to be called when the run-time PM workqueue is
+ * frozen (i.e. during system-wide suspend or hibernation) when it is guaranteed
+ * that no work items are being executed.
+ */
+void pm_cancel_runtime_resume(struct device *dev)
+{
+	spin_lock(&dev->power.lock);
+
+	if (dev->power.runtime_status & RPM_WAKE) {
+		work_clear_pending(&dev->power.runtime_work.work);
+		pm_runtime_reset(dev);
+	}
+
+	spin_unlock(&dev->power.lock);
+}
+EXPORT_SYMBOL_GPL(pm_cancel_runtime_resume);
+
+/**
+ * pm_runtime_disable - Disable run-time power management for given device.
+ * @dev: Device to handle.
+ *
+ * Increase the depth field in the device's dev_pm_info structure, which will
+ * cause the run-time PM functions above to return without doing anything.
+ * If there is a run-time PM operation in progress, wait for it to complete.
+ */
+void pm_runtime_disable(struct device *dev)
+{
+	might_sleep();
+
+	atomic_inc(&dev->power.depth);
+
+	if (dev->power.runtime_status & RPM_IN_PROGRESS)
+		wait_for_completion(&dev->power.work_done);
+}
+EXPORT_SYMBOL_GPL(pm_runtime_disable);
+
+/**
+ * pm_runtime_enable - Disable run-time power management for given device.
+ * @dev: Device to handle.
+ *
+ * Enable run-time power management for given device by decreasing the depth
+ * field in its dev_pm_info structure.
+ */
+void pm_runtime_enable(struct device *dev)
+{
+	if (!atomic_add_unless(&dev->power.depth, -1, 0))
+		dev_warn(dev, "PM: Excessive pm_runtime_enable()!\n");
+}
+EXPORT_SYMBOL_GPL(pm_runtime_enable);
+
+/**
+ * pm_runtime_init - Initialize run-time PM fields in given device object.
+ * @dev: Device object to handle.
+ */
+void pm_runtime_init(struct device *dev)
+{
+	pm_runtime_reset(dev);
+	spin_lock_init(&dev->power.lock);
+	atomic_set(&dev->power.depth, 1);
+	pm_suspend_check_children(dev, true);
+}
Index: linux-2.6/include/linux/pm_runtime.h
===================================================================
--- /dev/null
+++ linux-2.6/include/linux/pm_runtime.h
@@ -0,0 +1,63 @@
+/*
+ * pm_runtime.h - Device run-time power management helper functions.
+ *
+ * Copyright (C) 2009 Rafael J. Wysocki <rjw@xxxxxxx>
+ *
+ * This file is released under the GPLv2.
+ */
+
+#ifndef _LINUX_PM_RUNTIME_H
+#define _LINUX_PM_RUNTIME_H
+
+#include <linux/device.h>
+#include <linux/pm.h>
+
+#ifdef CONFIG_PM_RUNTIME
+
+extern struct workqueue_struct *pm_wq;
+
+extern void pm_runtime_init(struct device *dev);
+extern int pm_runtime_suspend(struct device *dev);
+extern void pm_request_suspend(struct device *dev, unsigned long delay);
+extern int pm_runtime_resume(struct device *dev);
+extern void pm_request_resume(struct device *dev);
+extern void pm_cancel_runtime_suspend(struct device *dev);
+extern void pm_cancel_runtime_resume(struct device *dev);
+extern void pm_runtime_disable(struct device *dev);
+extern void pm_runtime_enable(struct device *dev);
+
+static inline struct device *pm_work_to_device(struct work_struct *work)
+{
+	struct delayed_work *dw = to_delayed_work(work);
+	struct dev_pm_info *dpi;
+
+	dpi = container_of(dw, struct dev_pm_info, runtime_work);
+	return container_of(dpi, struct device, power);
+}
+
+static inline void pm_suspend_check_children(struct device *dev, bool enable)
+{
+	dev->power.suspend_skip_children = !enable;
+}
+
+#else /* !CONFIG_PM_RUNTIME */
+
+static inline void pm_runtime_init(struct device *dev) {}
+static inline int pm_runtime_suspend(struct device *dev) { return -ENOSYS; }
+static inline void pm_request_suspend(struct device *dev, unsigned long delay)
+{
+}
+static inline int pm_runtime_resume(struct device *dev) { return -ENOSYS; }
+static inline void pm_request_resume(struct device *dev) {}
+static inline void pm_cancel_runtime_suspend(struct device *dev) {}
+static inline void pm_cancel_runtime_resume(struct device *dev) {}
+static inline void pm_runtime_disable(struct device *dev) {}
+static inline void pm_runtime_enable(struct device *dev) {}
+
+static inline void pm_suspend_check_children(struct device *dev, bool enable)
+{
+}
+
+#endif /* !CONFIG_PM_RUNTIME */
+
+#endif
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
@@ -21,6 +21,7 @@
 #include <linux/kallsyms.h>
 #include <linux/mutex.h>
 #include <linux/pm.h>
+#include <linux/pm_runtime.h>
 #include <linux/resume-trace.h>
 #include <linux/rwsem.h>
 #include <linux/interrupt.h>
@@ -88,6 +89,7 @@ void device_pm_add(struct device *dev)
 	}
 
 	list_add_tail(&dev->power.entry, &dpm_list);
+	pm_runtime_init(dev);
 	mutex_unlock(&dpm_list_mtx);
 }
 
@@ -507,6 +509,7 @@ static void dpm_complete(pm_message_t st
 		get_device(dev);
 		if (dev->power.status > DPM_ON) {
 			dev->power.status = DPM_ON;
+			pm_runtime_enable(dev);
 			mutex_unlock(&dpm_list_mtx);
 
 			device_complete(dev, state);
@@ -753,6 +756,7 @@ static int dpm_prepare(pm_message_t stat
 
 		get_device(dev);
 		dev->power.status = DPM_PREPARING;
+		pm_runtime_disable(dev);
 		mutex_unlock(&dpm_list_mtx);
 
 		error = device_prepare(dev, state);
@@ -760,6 +764,7 @@ static int dpm_prepare(pm_message_t stat
 		mutex_lock(&dpm_list_mtx);
 		if (error) {
 			dev->power.status = DPM_ON;
+			pm_runtime_enable(dev);
 			if (error == -EAGAIN) {
 				put_device(dev);
 				continue;
Index: linux-2.6/drivers/base/dd.c
===================================================================
--- linux-2.6.orig/drivers/base/dd.c
+++ linux-2.6/drivers/base/dd.c
@@ -23,6 +23,7 @@
 #include <linux/kthread.h>
 #include <linux/wait.h>
 #include <linux/async.h>
+#include <linux/pm_runtime.h>
 
 #include "base.h"
 #include "power/power.h"
@@ -202,8 +203,12 @@ int driver_probe_device(struct device_dr
 	pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
 		 drv->bus->name, __func__, dev_name(dev), drv->name);
 
+	pm_runtime_disable(dev);
+
 	ret = really_probe(dev, drv);
 
+	pm_runtime_enable(dev);
+
 	return ret;
 }
 
@@ -306,6 +311,8 @@ static void __device_release_driver(stru
 
 	drv = dev->driver;
 	if (drv) {
+		pm_runtime_disable(dev);
+
 		driver_sysfs_remove(dev);
 
 		if (dev->bus)
@@ -320,6 +327,8 @@ static void __device_release_driver(stru
 		devres_release_all(dev);
 		dev->driver = NULL;
 		klist_remove(&dev->p->knode_driver);
+
+		pm_runtime_enable(dev);
 	}
 }
 
Index: linux-2.6/Documentation/power/runtime_pm.txt
===================================================================
--- /dev/null
+++ linux-2.6/Documentation/power/runtime_pm.txt
@@ -0,0 +1,250 @@
+Run-time Power Management Framework for I/O Devices
+
+(C) 2009 Rafael J. Wysocki <rjw@xxxxxxx>, Novell Inc.
+
+1. Introduction
+
+The support for run-time power management (run-time PM) of I/O devices is
+provided at the power management core (PM core) level by means of:
+
+* The power management workqueue pm_wq in which bus types and device drivers can
+  put their PM-related work items.  It is strongly recommended that pm_wq be
+  used for queueing all work items related to run-time PM, because this allows
+  them to be synchronized with system-wide power transitions.  pm_wq is declared
+  in include/linux/pm_runtime.h and defined in kernel/power/main.c.
+
+* A number of run-time PM fields in the 'power' member of 'struct device' (which
+  is of the type 'struct dev_pm_info', defined in include/linux/pm.h) that can
+  be used for synchronizing run-time PM operations with one another.
+
+* Three device run-time PM callbacks in 'struct dev_pm_ops' (defined in
+  include/linux/pm.h).
+
+* A set of helper functions defined in drivers/base/power/runtime.c that can be
+  used for carrying out run-time PM operations in such a way that the
+  synchronization between them is taken care of by the PM core.  Bus types and
+  device drivers are encouraged to use these functions.
+
+The device run-time PM fields defined in 'struct dev_pm_info', the helper
+funtions and the run-time PM callbacks defined in 'struct dev_pm_ops' are
+described in what follows.
+
+2. Run-time PM Helper Functions and Device Fields
+
+The following helper functions are defined in drivers/base/power/runtime.c
+and include/linux/pm_runtime.h:
+
+* void pm_runtime_init(struct device *dev);
+* void pm_runtime_enable(struct device *dev);
+* void pm_runtime_disable(struct device *dev);
+* int pm_runtime_suspend(struct device *dev);
+* void pm_request_suspend(struct device *dev, unsigned long delay);
+* int pm_runtime_resume(struct device *dev);
+* void pm_request_resume(struct device *dev);
+* void pm_cancel_runtime_suspend(struct device *dev);
+* void pm_cancel_runtime_resume(struct device *dev);
+* void pm_suspend_check_children(struct device *dev, bool enable);
+
+pm_runtime_init() initializes the run-time PM fields in the 'power' member of
+the device object.  It is called during the initialization of the device object,
+in drivers/base/power/main.c:device_pm_add().
+
+pm_runtime_enable() and pm_runtime_disable() are used to enable and disable,
+respectively, pm_runtime_suspend(), pm_request_suspend(), pm_runtime_resume(),
+and pm_request_resume().  They do it by decreasing and increasing, respectively,
+the 'power.depth' field of 'struct device'.  If the value of this field is
+greater than 0, pm_runtime_suspend(), pm_request_suspend(), pm_runtime_resume(),
+and pm_request_resume() return immediately without doing anything and -EBUSY is
+returned by pm_runtime_suspend() and pm_runtime_resume().  Therefore, if
+pm_runtime_disable() is called several times in a row for the same device, it
+has to be balanced by the appropriate number of pm_runtime_enable() calls so
+that the other run-time PM functions can be used for that device.  The initial
+value of 'power.depth', as set by pm_runtime_init(), is 1.
+
+pm_runtime_disable() and pm_runtime_enable() are used by the device core to
+disable the run-time PM of the device temporarily during device proble and
+removal as well as during system-wide power transitions (i.e. system-wide
+suspend or hibernation, or resume from a system sleep state).
+
+pm_runtime_suspend(), pm_request_suspend(), pm_runtime_resume(),
+and pm_request_resume() use the 'power.runtime_status' and
+'power.suspend_aborted' fields of 'struct device' for mutual synchronization.
+These fields are initialized by pm_runtime_init() and set to RPM_ACTIVE and
+'false', respectively.
+
+pm_request_suspend() is used to queue up a suspend request for an active device.
+If the run-time PM status of the device (i.e. the value of the
+'power.runtime_status' field in 'struct device') is different from RPM_ACTIVE,
+it returns immediately.  Otherwise, it changes the device's run-time PM status
+to RPM_IDLE and puts a request to execute pm_runtime_suspend() into pm_wq.  The
+'delay' argument is used to specify time to wait before the request will be
+completed, in jiffies.
+
+pm_runtime_suspend() is used to carry out a run-time suspend of an active
+device.  It is called either by the PM core, to complete a request queued up by
+pm_request_suspend(), or directly by a bus type or device driver.
+* It returns immediately if the RPM_SUSPENDED bit is set in the device's
+  run-time PM status field ('power.runtime_status').
+* It returns -EAGAIN if at least one of the RPM_WAKE and RPM_RESUMING bits is
+  set the device's run-time PM status field.
+* If the device's run-time PM status is RPM_IDLE and 'power.suspend_aborted'
+  flag is set for it, the device's run-time PM status is set to RPM_ACTIVE and
+  the function returns success.
+* If the device's children are not suspended and the
+  'power.suspend_skip_children' flag is not set for it, -EAGAIN is returned.
+* If the device's run-time PM status is RPM_SUSPENDING, which means that another
+  instance of pm_runtime_suspend() is running at the same time for the same
+  device, the function waits for the other instance to complete and returns the
+  error code (or success) returned by it.
+If none of the above takes place, the device's run-time PM status is set to
+RPM_SUSPENDING and the device bus type's ->runtime_suspend() callback is
+executed, which is responsible for handling the device as appropriate (for
+example, it may choose to execute the device driver's ->runtime_suspend()
+callback or to carry out any other suitable action depending on the bus type).
+Next:
+* If it completes successfully, the RPM_SUSPENDED bit is set and the
+  RPM_SUSPENDING bit is cleared in the device's run-time PM status field.  Once
+  that has happened, the device is regarded by the PM core as suspended, but it
+  need not mean that the device has been put into a low power state.  What
+  really occurs to the device at this point totally depends on its bus type (it
+  may depend on the device's driver if the bus type chooses to call it).
+  Additionally, if the device bus type's ->runtime_suspend() callback completes
+  successfully, the device bus type's ->runtime_idle() callback is executed for
+  the device's parent if there is one and if all of its children are suspended
+  (or the 'power.suspend_skip_children' flag is set for it).
+* If either -EBUSY or -EAGAIN is returned, the device's run-time PM status is
+  set to RPM_ACTIVE.
+* If another error code is returned, the device's run-time PM status is set to
+  RPM_ERROR and the PM core will refuse to run pm_runtime_suspend(),
+  pm_request_suspend(), pm_runtime_resume(), and pm_request_resume() until the
+  status is changed to either RPM_ACTIVE or RPM_SUSPENDED by the device's bus
+  type or driver.
+Finally, pm_runtime_suspend() returns the error code (or success) returned by
+the device bus type's ->runtime_suspend() callback.
+
+pm_request_resume() is used to queue up a resume request for a device that is
+suspended, suspending or has a suspend request pending.
+* If a suspend request is pending for the device (i.e. the device's run-time PM
+  status is RPM_IDLE), it is cancelled and the function returns.
+* If the device is not suspended or suspending (i.e. none of the RPM_SUSPENDED
+  and RPM_SUSPENDING bits is set in the device's run-time PM status field), the
+  function returns.
+* If the device's parent is inactive, a resume request is scheduled for the
+  parent and the function is restarted.
+If none of the above happens, the RPM_WAKE bit is set in the device's run-time
+PM status field and the request to execute pm_runtime_resume() is put into
+pm_wq.
+
+pm_runtime_resume() is used to carry out a run-time resume of a device that is
+suspended, suspending or has a suspend request pending.  It is called either by
+the PM core, to complete a request queued up by pm_request_resume(), or
+directly by a bus type or device driver.
+* It returns immediately if the device's run-time PM status is RPM_ACTIVE.
+* If there's a suspend request pending for the device (i.e. the device's
+  run-time PM status is RPM_IDLE), it is cancelled and the function returns
+  success.
+* If the device is suspending (i.e. the RPM_SUSPENDING bit is set in the
+  device's run-time PM status field), the function waits for the suspend
+  operation to complete and restarts itself.
+* If the device is suspended (i.e. the RPM_SUSPENDED bit is set in the device's
+  run-time PM status field), the device's parent exists and is not active (i.e.
+  the parent's run-time PM status is not RPM_ACTIVE), pm_runtime_resume() is
+  called (recursively) for the parent and the function is restarted.
+* If the device is resuming (i.e. the device's run-time PM status is
+  RPM_RESUMING), which means that another instance of pm_runtime_resume() is
+  running at the same time for the same device, the function waits for the other
+  instance to complete and returns the result returned by it.
+If none of the above happens, the device's run-time PM status is set to
+RPM_RESUMING and the device bus type's ->runtime_resume() callback is executed,
+which is responsible for handling the device as appropriate (for example, it may
+choose to execute the device driver's ->runtime_resume() callback or to carry
+out any other suitable action depending on the bus type).  Next:
+* If it completes successfully, the device's run-time PM status is set to
+  RPM_ACTIVE, which means that the device is fully operational.  Thus, the
+  device bus type's ->runtime_resume() callback, when it is about to return
+  success, _must_ _ensure_ that this really is the case (i.e. when it returns,
+  the device _must_ be able to complete I/O operations as needed).
+* If either -EBUSY or -EAGAIN is returned, the device's run-time PM status is
+  set to RPM_SUSPENDED.
+* If another error code is returned, the device's run-time PM status is set to
+  RPM_ERROR and the PM core will refuse to run pm_runtime_suspend(),
+  pm_request_suspend(), pm_runtime_resume(), and pm_request_resume() until the
+  status is changed to either RPM_ACTIVE or RPM_SUSPENDED by the device's bus
+  type or driver.
+Finally, pm_runtime_resume() returns the error code (or success) returned by
+the device bus type's ->runtime_resume() callback.
+
+pm_cancel_runtime_suspend() is used to cancel a pending suspend request for an
+active device, but it can only be called when the run-time PM of the device
+is disabled.  It is supposed to be used during system-wide power transitions.
+
+pm_cancel_runtime_resume() is used to cancel a pending suspend request for
+a suspended device.  It can only be called when the run-time PM of the device
+is disabled and it is supposed to be used during system-wide power transitions.
+
+pm_suspend_check_children() is used to set or unset the
+'power.suspend_skip_children' flag in 'struct device'.  If the 'enabled'
+argument is 'true', the field is set to 0, and if 'enable' is 'false', the field
+is set to 1.  The default value of 'power.suspend_skip_children', as set by
+pm_runtime_init(), is 0.
+
+3. Device Run-time PM Callbacks
+
+There are three device run-time PM callbacks defined in 'struct dev_pm_ops':
+
+struct dev_pm_ops {
+	...
+	int (*runtime_suspend)(struct device *dev);
+	int (*runtime_resume)(struct device *dev);
+	void (*runtime_idle)(struct device *dev);
+	...
+};
+
+The ->runtime_suspend() callback is executed by pm_runtime_suspend() for the bus
+type of the device being suspended.  The bus type's callback is then _fully_
+_responsible_ for handling the device as appropriate, which may, but need not
+include executing the device driver's ->runtime_suspend() callback (from the PM
+core's point of view it is not necessary to implement a ->runtime_suspend()
+callback in a device driver as long as the bus type's ->runtime_suspend() knows
+what to do to handle the device).
+* Once the bus type's ->runtime_suspend() callback has returned successfully,
+  the PM core regards the device as suspended, which need not mean that the
+  device has been put into a low power state.  It is supposed to mean, however,
+  that the device will not commuticate with the CPU(s) and RAM until the bus
+  type's ->runtime_resume() callback is executed for it.
+* If the bus type's ->runtime_suspend() callback returns -EBUSY or -EAGAIN, the
+  device's run-time PM status is set to RPM_ACTIVE, which measn that the device
+  _must_ be fully operational one this has happened.
+* If the bus type's ->runtime_suspend() callback returns an error code different
+  from -EBUSY or -EAGAIN, the PM core regards this as an unrecoverable error and
+  will refuse to run the helper functions described in Section 1 until the
+  status is changed to either RPM_SUSPENDED or RPM_ACTIVE by the device's bus
+  type or driver.
+
+The ->runtime_resume() callback is executed by pm_runtime_resume() for the bus
+type of the device being woken up.  The bus type's callback is then _fully_
+_responsible_ for handling the device as appropriate, which may, but need not
+include executing the device driver's ->runtime_resume() callback (from the PM
+core's point of view it is not necessary to implement a ->runtime_resume()
+callback in a device driver as long as the bus type's ->runtime_resume() knows
+what to do to handle the device).
+* Once the bus type's ->runtime_resume() callback has returned successfully,
+  the PM core regards the device as fully operational, which means that the
+  device _must_ be able to complete I/O operations as needed.
+* If the bus type's ->runtime_resume() callback returns -EBUSY or -EAGAIN, the
+  device's run-time PM status is set to RPM_SUSPENDED, which is supposed to mean
+  that the device will not commuticate with the CPU(s) and RAM until the bus
+  type's ->runtime_resume() callback is executed for it.
+* If the bus type's ->runtime_resume() callback returns an error code different
+  from -EBUSY or -EAGAIN, the PM core regards this as an unrecoverable error and
+  will refuse to run the helper functions described in Section 1 until the
+  status is changed to either RPM_SUSPENDED or RPM_ACTIVE by the device's bus
+  type or driver.
+
+The ->runtime_idle() callback is executed by pm_runtime_suspend() for the bus
+type of a device the children of which are all suspended (or which has the
+'power.suspend_skip_children' flag set).  The action carried out by this
+callback is totally dependent on the bus type in question, but the expected
+action is to check if the device can be suspended (i.e. if all of the conditions
+necessary for suspending the device are met) and to queue up a suspend request
+for the device if that is the case.
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