[patch update 2 fix] PM: Introduce core framework for run-time PM of I/O devices

Rafael J. Wysocki
2009-06-16T22:33:21Z

On Tuesday 16 June 2009, Rafael J. Wysocki wrote:
> On Tuesday 16 June 2009, Alan Stern wrote:
> > On Tue, 16 Jun 2009, Rafael J. Wysocki wrote:
> > > > Since pm_runtime_resume() takes care of powering up the parent, there's
> > > > no need for pm_request_resume() to worry about it also.
> > >
> > > But still it won't hurt to do it IMO, because the parents are then going
> > > to be resumed before our pm_runtime_resume() is called.
> >
> > It's extra code that isn't needed. In essence, you are trading code
> > space for a shorter runtime stack.
>
> That's correct. I think the code size increase is small and it's better to
> keep the stack as small as reasonably possible.
>
> > > > The documentation should mention that the runtime_suspend method is
> > > > supposed to enable remote wakeup if it as available and if
> > > > device_may_wakeup(dev) is true.
> > >
> > > Well, I thought that was obvious. :-)
> >
> > Sometimes it doesn't hurt to state the obvious! :-)
>
> Sure.
>
> In the meantime I updated the patch once again. I addressed your last
> comments in this version and added the possibility to resume with blocking
> suspend (ie. after such a resume pm_runtime_suspend() and pm_request_suspend()
> will return immediately intil a special function is called).
>
> I also fixed a couple of bugs. :-)

Sorry for the broken patch. My mailer started to wordwrap messages
automatically and I didn't notice.

The correct patch is appended.

Best,
Rafael

---
From: Rafael J. Wysocki <rjw@sisk.pl>
Subject: PM: Introduce core framework for run-time PM of I/O devices

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@sisk.pl>
---
Documentation/power/runtime_pm.txt | 311 +++++++++++++++++++++++
drivers/base/dd.c | 9
drivers/base/power/Makefile | 1
drivers/base/power/main.c | 5
drivers/base/power/runtime.c | 499 +++++++++++++++++++++++++++++++++++++
include/linux/pm.h | 97 ++++++-
include/linux/pm_runtime.h | 112 ++++++++
kernel/power/Kconfig | 14 +
kernel/power/main.c | 17 +
9 files changed, 1062 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 +205,9 @@ struct dev_pm_ops {
int (*thaw_noirq)(struct device *dev);
int (*poweroff_noirq)(struct device *dev);
int (*restore_noirq)(struct device *dev);
+ int (*runtime_suspend)(struct device *dev);
+ int (*runtime_resume)(struct device *dev);
+ void (*runtime_idle)(struct device *dev);
};

/**
@@ -315,14 +341,79 @@ 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_GRACE 0x20
+#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 | RPM_GRACE)
+#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:6;
+ 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 +1,499 @@
+/*
+ * drivers/base/power/runtime.c - Helper functions for device run-time PM
+ *
+ * Copyright (c) 2009 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
+ *
+ * This file is released under the GPLv2.
+ */
+
+#include <linux/pm_runtime.h>
+#include <linux/jiffies.h>
+
+/**
+ * __pm_runtime_change_status - Change the run-time PM status of a device.
+ * @dev: Device to handle.
+ * @status: Expected current run-time PM status of the device.
+ * @new_status: New value of the device's run-time PM status.
+ *
+ * Change the run-time PM status of the device to @new_status if its current
+ * value is equal to @status.
+ */
+void __pm_runtime_change_status(struct device *dev, unsigned int status,
+ unsigned int new_status)
+{
+ unsigned long flags;
+
+ if (atomic_read(&dev->power.depth) > 0)
+ return;
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ if (dev->power.runtime_status == status)
+ dev->power.runtime_status = new_status;
+
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+}
+EXPORT_SYMBOL_GPL(__pm_runtime_change_status);
+
+/**
+ * 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.
+ * @sync: If unset, the funtion has been called via pm_wq.
+ *
+ * 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, bool sync)
+{
+ int error = -EINVAL;
+
+ if (atomic_read(&dev->power.depth) > 0)
+ return -EBUSY;
+
+ spin_lock(&dev->power.lock);
+
+ if (dev->power.runtime_status == RPM_ERROR) {
+ goto out;
+ } else if (dev->power.runtime_status & RPM_SUSPENDED) {
+ error = 0;
+ goto out;
+ } else if ((dev->power.runtime_status & RPM_NO_SUSPEND)
+ || (!sync && dev->power.suspend_aborted)) {
+ /*
+ * Device is resuming or in a post-resume grace period or
+ * there's a resume request pending, or a pending suspend
+ * request has just been cancelled and we're running as a result
+ * of this request.
+ */
+ 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;
+ } else if (pm_check_children(dev)) {
+ /*
+ * We can only suspend the device if all of its children have
+ * been suspended.
+ */
+ dev->power.runtime_status = RPM_ACTIVE;
+ error = -EAGAIN;
+ goto out;
+ }
+
+ 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_all(&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), false);
+}
+
+/**
+ * pm_request_suspend - Schedule run-time suspend of given device.
+ * @dev: Device to suspend.
+ * @msec: Time to wait before attempting to suspend the device, in milliseconds.
+ */
+void pm_request_suspend(struct device *dev, unsigned int msec)
+{
+ unsigned long flags;
+ unsigned long delay = msecs_to_jiffies(msec);
+
+ 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.
+ */
+static void pm_cancel_suspend(struct device *dev)
+{
+ cancel_delayed_work(&dev->power.runtime_work);
+ dev->power.runtime_status &= RPM_GRACE;
+ dev->power.suspend_aborted = true;
+}
+
+/**
+ * __pm_runtime_resume - Run a device bus type's runtime_resume() callback.
+ * @dev: Device to resume.
+ * @grace: If set, force a post-resume grace period.
+ *
+ * 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, bool grace)
+{
+ int error = -EINVAL;
+
+ 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_ERROR) {
+ goto out_unlock;
+ } if (!(dev->power.runtime_status & ~RPM_GRACE)) {
+ /* Device is active or in a post-resume grace period. */
+ error = 0;
+ 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);
+ if (grace)
+ dev->power.runtime_status |= RPM_GRACE;
+ error = 0;
+ 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_GRACE)) {
+ 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, false);
+ if (error)
+ return error;
+
+ goto repeat;
+ }
+
+ if (dev->power.runtime_status == RPM_RESUMING) {
+ if (grace)
+ dev->power.runtime_status |= RPM_GRACE;
+ 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;
+ }
+
+ /* The RPM_GRACE bit may be set in runtime_status. */
+ dev->power.runtime_status &= ~(RPM_WAKE | RPM_SUSPENDED);
+ dev->power.runtime_status |= RPM_RESUMING;
+ if (grace)
+ dev->power.runtime_status |= RPM_GRACE;
+ 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);
+
+ dev->power.runtime_status &= ~RPM_RESUMING;
+ switch (error) {
+ case -EAGAIN:
+ case -EBUSY:
+ dev->power.runtime_status = RPM_SUSPENDED;
+ break;
+ default:
+ dev->power.runtime_status = RPM_ERROR;
+ }
+ dev->power.runtime_error = error;
+ complete_all(&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 without forcing a grace period after the resume.
+ */
+static void pm_runtime_resume_work(struct work_struct *work)
+{
+ __pm_runtime_resume(pm_work_to_device(work), false);
+}
+
+/**
+ * pm_request_resume - Schedule run-time resume of given device.
+ * @dev: Device to resume.
+ * @grace: If set, force a post-resume grace period.
+ */
+void __pm_request_resume(struct device *dev, bool grace)
+{
+ 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);
+ if (grace)
+ dev->power.runtime_status |= RPM_GRACE;
+ 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);
+
+ /* The parent is suspending, suspended or idle. Wake it up. */
+ __pm_request_resume(dev->parent, false);
+
+ 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;
+ if (grace)
+ dev->power.runtime_status |= RPM_GRACE;
+ 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);
+ dev->power.runtime_status = RPM_ACTIVE;
+ }
+
+ 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);
+ dev->power.runtime_status &= ~(RPM_WAKE | RPM_GRACE);
+ }
+
+ 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)
+{
+ spin_lock_init(&dev->power.lock);
+ dev->power.runtime_status = RPM_ACTIVE;
+ 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 +1,112 @@
+/*
+ * pm_runtime.h - Device run-time power management helper functions.
+ *
+ * Copyright (C) 2009 Rafael J. Wysocki <rjw@sisk.pl>
+ *
+ * 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 void __pm_runtime_change_status(struct device *dev, unsigned int status,
+ unsigned int new_status);
+extern int __pm_runtime_suspend(struct device *dev, bool sync);
+extern void pm_request_suspend(struct device *dev, unsigned int msec);
+extern int __pm_runtime_resume(struct device *dev, bool grace);
+extern void __pm_request_resume(struct device *dev, bool grace);
+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 void __pm_runtime_change_status(struct device *dev,
+ unsigned int status,
+ unsigned int new_status) {}
+static inline int __pm_runtime_suspend(struct device *dev, bool sync)
+{
+ return -ENOSYS;
+}
+static inline void pm_request_suspend(struct device *dev, unsigned int msec) {}
+static inline int __pm_runtime_resume(struct device *dev, bool grace)
+{
+ return -ENOSYS;
+}
+static inline void __pm_request_resume(struct device *dev, bool grace) {}
+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 */
+
+static inline int pm_runtime_suspend(struct device *dev)
+{
+ return __pm_runtime_suspend(dev, true);
+}
+
+static inline int pm_runtime_resume(struct device *dev)
+{
+ return __pm_runtime_resume(dev, false);
+}
+
+static inline int pm_runtime_resume_grace(struct device *dev)
+{
+ return __pm_runtime_resume(dev, true);
+}
+
+static inline void pm_request_resume(struct device *dev)
+{
+ __pm_request_resume(dev, false);
+}
+
+static inline void pm_request_resume_grace(struct device *dev)
+{
+ __pm_request_resume(dev, true);
+}
+
+static inline void pm_runtime_clear_active(struct device *dev)
+{
+ __pm_runtime_change_status(dev, RPM_ERROR, RPM_ACTIVE);
+}
+
+static inline void pm_runtime_clear_suspended(struct device *dev)
+{
+ __pm_runtime_change_status(dev, RPM_ERROR, RPM_SUSPENDED);
+}
+
+static inline void pm_runtime_release(struct device *dev)
+{
+ __pm_runtime_change_status(dev, RPM_GRACE, RPM_ACTIVE);
+}
+
+#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 +1,311 @@
+Run-time Power Management Framework for I/O Devices
+
+(C) 2009 Rafael J. Wysocki <rjw@sisk.pl>, 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 queuing 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
+functions and the run-time PM callbacks defined in 'struct dev_pm_ops' are
+described below.
+
+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);
+* int pm_runtime_resume_grace(struct device *dev);
+* void pm_request_resume(struct device *dev);
+* void pm_request_resume_grace(struct device *dev);
+* void pm_runtime_release(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);
+
+* void pm_runtime_clear_active(struct device *dev) {}
+* void pm_runtime_clear_suspended(struct device *dev) {}
+
+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, all of the run-time PM core operations. 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 so on return immediately without
+doing anything and -EBUSY is returned by pm_runtime_suspend(),
+pm_runtime_resume() and pm_runtime_resume_grace(). 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 core functions can be used for that device. The
+initial value of 'power.depth', as set by pm_runtime_init(), is 1 (i.e. the
+run-time PM of the device is initially disabled).
+
+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 probe 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(),
+pm_runtime_resume_grace(), pm_request_resume(), and pm_request_resume_grace()
+use the 'power.runtime_status' and 'power.suspend_aborted' fields of
+'struct device' for mutual synchronization. The 'power.runtime_status' field,
+called the device's run-time PM status in what follows, is set to RPM_ACTIVE by
+pm_runtime_init().
+
+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
+(i.e. the device is not active from the PM core standpoint), it returns
+immediately. Otherwise, it changes the device's run-time PM status to RPM_IDLE
+and puts a request to suspend the device into pm_wq. The 'msec' argument is
+used to specify the time to wait before the request will be completed, in
+milliseconds. It is valid to call this function from interrupt context.
+
+pm_runtime_suspend() is used to carry out a run-time suspend of an active
+device. It is called directly by a bus type or device driver. An asynchronous
+version of it is called by the PM core, to complete a request queued up by
+pm_request_suspend(). The only difference between them is the handling of
+situations when a queued up suspend request has just been cancelled. Apart from
+this, they work in the same way.
+* If the device is suspended (i.e. the RPM_SUSPENDED bit is set in the device's
+ run-time PM status field, 'power.runtime_status'), success is returned.
+* If the device is about to resume or is in a post-resume grace period (i.e. at
+ least one of the RPM_WAKE, RPM_RESUMING, and RPM_GRACE bits are set in the
+ device's run-time PM status field), -EAGAIN is returned. -EAGAIN is also
+ returned if the function has been called via pm_wq as a result of a cancelled
+ suspend request (the 'power.suspend_aborted' field is used for this purpose).
+* If the device is suspending (i.e. its 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 the device's children are not suspended and the
+ 'power.suspend_skip_children' flag is not set for it, the device's run-time PM
+ status is set to RPM_ACTIVE and -EAGAIN is returned.
+If none of the above takes place, the device's run-time PM status is set to
+RPM_SUSPENDING and its bus type's ->runtime_suspend() callback is executed.
+This callback 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).
+* 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 carry out any run-time PM operations
+ for it until the status is cleared by its bus type or driver with the help of
+ either pm_runtime_clear_active(), or pm_runtime_clear_suspended().
+Finally, pm_runtime_suspend() returns the error code (or success) returned by
+the device bus type's ->runtime_suspend() callback. If the device's bus type
+doesn't implement ->runtime_suspend(), -EINVAL is returned and the device's
+run-time PM status is set to RPM_ERROR.
+
+pm_request_resume() and pm_request_resume_grace() are used to queue up a resume
+request for a device that is suspended, suspending or has a suspend request
+pending. The difference between them is that pm_request_resume_grace() causes
+the RPM_GRACE bit to be set in the device's run-time PM status field, which
+prevents the PM core from suspending the device or queuing up a suspend request
+for it until the RPM_GRACE bit is cleared with the help of pm_runtime_release().
+Apart from this, they work in the same way.
+* If a suspend request is pending for the device (i.e. the device's run-time PM
+ status is RPM_IDLE), it is cancelled, the 'power.suspend_aborted' flag is set
+ for the device, the RPM_IDLE bit is cleared in the device's run-time PM status
+ field and the function returns (pm_request_resume_grace() additionally sets
+ the RPM_GRACE bit in the device's run-time PM status field).
+* 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 (i.e. at least one of the RPM_IDLE,
+ RPM_SUSPENDING, and RPM_SUSPENDED bits is set in its run-time PM status
+ field), a resume request is (recursively) 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() and pm_runtime_resume_grace() are used to carry out a
+run-time resume of a device that is suspended, suspending or has a suspend
+request pending. They are 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.
+The difference between them is that pm_request_resume_grace() causes the
+RPM_GRACE bit to be set in the device's run-time PM status field, which prevents
+the PM core from suspending the device or queuing up a suspend request for it
+until the RPM_GRACE bit is cleared with the help of pm_runtime_release(). Apart
+from this, they work in the same way.
+* If the device is active (i.e. all of the bits in its run-time PM status are
+ clear, possibly except for RPM_GRACE), success is returned.
+* 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, the 'power.suspend_aborted'
+ flag is set for the device, the RPM_IDLE bit is cleared in its run-time PM
+ status field and the function returns success (pm_runtime_resume_grace()
+ additionally sets the RPM_GRACE bit in the device's run-time PM status field).
+* If the device is suspending (i.e. the RPM_SUSPENDING bit is set in its
+ 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 or RPM_GRACE), the parent is
+ resumed (recursively) and the function restarts itself.
+* 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 RPM_WAKE and RPM_SUSPENDED bits are cleared
+and the RPM_RESUMING bit is set in the device's run-time PM status field. Next,
+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).
+* If it completes successfully, the device's run-time PM status is set to
+ 'active' (i.e. the device's run-time PM status field is either RPM_ACTIVE, or
+ RPM_GRACE), 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
+ success, the device _must_ be able to carry out 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 carry out any run-time PM operations
+ for it until the status is cleared by its bus type or driver with the help of
+ either pm_runtime_clear_active(), or pm_runtime_clear_suspended().
+Finally, pm_runtime_resume() returns the error code (or success) returned by
+the device bus type's ->runtime_resume() callback. If the device's bus type
+doesn't implement ->runtime_resume(), -EINVAL is returned and the device's
+run-time PM status is set to RPM_ERROR.
+
+pm_runtime_release() is used to clear the RPM_GRACE bit in the device's run-time
+PM status field. This bit, if set, causes the PM core to refuse to suspend
+the device or to queue up a suspend request for it. In particular, it causes
+pm_runtime_suspend() to return -EAGAIN without doing anything else. This may
+be useful if the device is resumed for a specific task and it shouldn't be
+suspended until the task is complete, but there are many potential sources of
+suspend requests that could disturb it.
+
+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.
+
+pm_runtime_clear_active() is used to change the device's run-time PM status
+field from RPM_ERROR to RPM_ACTIVE.
+
+pm_runtime_clear_suspended() is used to change the device's run-time PM status
+field from RPM_ERROR to RPM_SUSPENDED.
+
+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 communicate 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 means 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.
+In particular, it is recommended that ->runtime_suspend() return -EBUSY or
+-EAGAIN if device_may_wakeup() returns 'false' for the device. On the other
+hand, if device_may_wakeup() returns 'true' for the device and the device is put
+into a low power state during the execution of ->runtime_suspend(), it is
+expected that remote wake-up (i.e. hardware mechanism allowing the device to
+request a change of its power state, such as PCI PME) will be enabled for the
+device. Generally, remote wake-up should be enabled whenever the device is put
+into a low power state at run time and is expected to receive input from the
+outside of the system.
+
+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 communicate 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.