[patch update 3] PM: Introduce core framework for run-time PM of I/O devices

Rafael J. Wysocki
2009-06-20T23:39:21Z

On Saturday 20 June 2009, Alan Stern wrote:
> On Sat, 20 Jun 2009, Rafael J. Wysocki wrote:
>
> > I think we can grab a reference when queuing up a resume request and drop
> > it on the completion of it. This way, suspend will be locked while we're
> > waiting for the resume to run, which I think is what we want.
>
> But suspend is already blocked from the time a resume request is queued
> until the resume completes, unless the suspend was underway when the
> request was made. So that doesn't seem to make sense.
>
> This really all depends on how drivers use async autoresume. Here's
> one possible way they could be written:
>
> irq_handler() {
> status = pm_request_resume();
> if (status indicates the device is currently resumed)
> handle_the_IO();
> else
> save_the_IO();
> }
>
> runtime_resume_method() {
> handle_saved_IO();
> pm_request_suspend(); /* Could call pm_notify_idle instead */
> }
>
> The implications of this design are:
>
> pm_request_resume should return one code if the status already
> is RPM_WAKE and a different code if the resume request had to
> be queued (or one was already queued).

I did something like this in the patch below.

> pm_request_suspend should run very quickly, since it will be
> called after every I/O operation. Likewise, pm_request_resume
> should run very quickly if the status is RPM_ACTIVE or
> RPM_IDLE.

Hmm. pm_request_suspend() is really short, so it should be fast.
pm_request_resume() is a bit more complicated, though (it takes two spinlocks,
increases an atomic counter, possibly twice, and queues up a work item, also
in the RPM_IDLE case).

> In order to prevent autosuspends from occurring while I/O is
> in progress, the pm_request_resume call should increment the
> usage counter (if it had to queue the request) and the
> pm_request_suspend call should decrement it (maybe after
> waiting for the delay).

I don't want like pm_request_suspend() to do that, because it's valid to
call it many times in a row. (only the first request will be queued in such a
case).

I'd prefer the caller to do pm_request_resume_get() (please see the patch
below) to put a resume request into the queue and then pm_runtime_put_notify()
when it's done with the I/O. That will result in ->runtime_idle() being called
automatically if the device may be suspended.

> > OK, I think I'll try to do the counting, although it may be difficult to handle
> > all of the corner cases.
>
> No, I agree it's not worth worrying about for now. It can always be
> added later.

Well, I've done it already, so I'd prefer to keep it, unless it's broken. ;-)

> > > > > There might be some obscure other reason, but in general depth going
> > > > > to 0 means a delayed autosuspend request should be queued.
> > > >
> > > > OK there, but pm_runtime_disable() is called by the core in some places where
> > > > we'd rather not want the device to be suspended (like during a system-wide
> > > > power transitions).
> > >
> > > I'm not sure what you mean. I was talking about pm_runtime_enable
> > > (which decrements depth), not pm_runtime_disable (which increments it).
> > > When pm_runtime_enable finds that depth has gone to 0, it should queue
> > > a delayed autosuspend request.
> >
> > OK, but I don't think that queuing a request without notifying the bus type is
> > the right thing to do. IMO it's better to use ->runtime_idle() in that case
> > (in analogy with the situation in which the last child of a device has been
> > suspended).
>
> Agreed.
>
>
> > > Autosuspend is disallowed if:
> > >
> > > the driver doesn't support autosuspend;
> > >
> > > the usage counter is > 0;
> > >
> > > autosuspend has been disabled for this device;
> > >
> > > the driver requires remote wakeup during autosuspend
> > > but the user has disallowed wakeup.
> >
> > That's probably universal for all bus types and devices.
>
> Probably. But you haven't provided a way for the driver to indicate
> that it requires wakeup. It's not a big deal, since the
> runtime_suspend method can do its own checking.
>
> > > If everything else is okay but not enough time has elapsed since the
> > > device was last used, another delayed autosuspend request is queued and
> > > the current one fails with -EAGAIN.
> >
> > I wouldn't like to do the automatic queuing at the core level, simply because
> > the core may not have enough information to make a correct decision.
>
> Calling the notify_idle method would be good enough.
>
> > > The model for asynchronous operation is that the usage counter remains
> > > always at 0, and the driver updates the time-of-last-use field whenever
> > > an I/O operation starts or completes. The core keeps a delayed
> > > autosuspend request queued; each time the request runs it checks
> > > whether the device has been idle sufficiently long. If not it
> > > requeues itself; otherwise it carries out an autosuspend.
> >
> > Again, I think it's a bus type's decision whether or not to use such a
> > "permanent" suspend request.
>
> Ironically, this model is different from the one I outlined above.
> There's more than one way to do this, it's not clear which is best, and
> AFAIK none of them have been implemented in a real driver yet.
>
> > I think it probably is a good idea to store the time of last use in 'struct
> > device', so that bus types don't need to duplicate that field (all of them will
> > likely use it). I'm not sure about the delay, though. Well, I need some time
> > to think about it. :-)
>
> All bus types will want to implement _some_ delay; it doesn't make
> sense to power down a device immediately after every operation and then
> power it back up for the next operation.

Sure. But you can use the pm_request_resume()'s delay to achieve that
without storing the delay in 'struct device'. It seems.

> But the time scales of the delays may vary widely. Some devices might
> be able to power up in a millisecond or less; others will require
> seconds. The delays should be set accordingly.

Agreed.

OK

Below is a new patch. It's been reworked quite a bit since the previous
version I sent and I don't think there's anything I'd like to add to it at this
point, unless something is evidently wrong.

Best,
Rafael

---
From: Rafael J. Wysocki <rjw@sisk.pl>
Subject: PM: Introduce core framework for run-time PM of I/O devices (rev. 2)

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 | 416 ++++++++++++++++++++++++
drivers/base/dd.c | 9
drivers/base/power/Makefile | 1
drivers/base/power/main.c | 6
drivers/base/power/runtime.c | 617 +++++++++++++++++++++++++++++++++++++
include/linux/pm.h | 95 +++++
include/linux/pm_runtime.h | 148 ++++++++
kernel/power/Kconfig | 14
kernel/power/main.c | 17 +
9 files changed, 1320 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 +168,28 @@ 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.
+ * For example, if the device is behind a link which is about to be turned
+ * off, the device may remain at full power. Still, if the device does go
+ * to low power and if device_may_wakeup(dev) is true, remote wake-up
+ * (i.e. hardware mechanism allowing the device to request a change of its
+ * power state, such as PCI PME) should be enabled for it.
+ *
+ * @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 +207,9 @@ 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 +343,75 @@ 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 0x1F
+
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 suspend_work;
+ struct work_struct resume_work;
+ struct completion work_done;
+ unsigned int ignore_children:1;
+ unsigned int suspend_aborted:1;
+ unsigned int runtime_status:5;
+ int runtime_error;
+ atomic_t resume_count;
+ int child_count;
+ 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 +1,617 @@
+/*
+ * 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_get_child - Increment the counter of unsuspended children of a device.
+ * @dev: Device to handle;
+ */
+static void __pm_get_child(struct device *dev)
+{
+ dev->power.child_count++;
+}
+
+/**
+ * __pm_put_child - Decrement the counter of unsuspended children of a device.
+ * @dev: Device to handle;
+ */
+static void __pm_put_child(struct device *dev)
+{
+ if (dev->power.child_count > 0)
+ dev->power.child_count--;
+ else
+ dev_warn(dev, "Excessive %s!\n", __FUNCTION__);
+}
+
+/**
+ * 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.resume_count) > 0)
+ return;
+
+ if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_idle)
+ dev->bus->pm->runtime_idle(dev);
+}
+
+/**
+ * pm_runtime_put - Decrement the resume counter of a device.
+ * @dev: Device to handle.
+ *
+ * Decrement the resume counter of a device, check if it went down to zero and
+ * notify the device's bus type in that case.
+ */
+void pm_runtime_put_notify(struct device *dev)
+{
+ pm_runtime_put(dev);
+
+ if (pm_children_suspended(dev))
+ pm_runtime_notify_idle(dev);
+}
+EXPORT_SYMBOL_GPL(pm_runtime_put_notify);
+
+/**
+ * __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)
+{
+ struct device *parent = NULL;
+ unsigned long parflags = 0, flags;
+ int error = -EINVAL;
+
+ might_sleep();
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ repeat:
+ if (dev->power.runtime_status == RPM_ERROR) {
+ goto out;
+ } else if (dev->power.runtime_status & RPM_SUSPENDED) {
+ error = 0;
+ goto out;
+ } else if (atomic_read(&dev->power.resume_count) > 0
+ || (!sync && dev->power.runtime_status == RPM_IDLE
+ && dev->power.suspend_aborted)) {
+ /*
+ * We're forbidden to suspend the device (eg. it may be
+ * resuming) or a pending suspend request has just been
+ * cancelled (by a concurrent suspend) and we're running as a
+ * result of that request.
+ */
+ error = -EAGAIN;
+ goto out;
+ } else if (dev->power.runtime_status & RPM_SUSPENDING) {
+ /*
+ * Another suspend is running in parallel with us. Wait for it
+ * to complete and return.
+ */
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+
+ wait_for_completion(&dev->power.work_done);
+
+ return dev->power.runtime_error;
+ } else if (sync && dev->power.runtime_status == RPM_IDLE
+ && !dev->power.suspend_aborted) {
+ /*
+ * Suspend request is pending, but we're not running as a result
+ * of that request, so cancel it. Since we're not clearing the
+ * RPM_IDLE bit now, no new suspend requests will be queued up
+ * while the pending one is waited for to finish.
+ */
+ dev->power.suspend_aborted = true;
+
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+
+ cancel_delayed_work_sync(&dev->power.suspend_work);
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ /* Repeat if anything has changed. */
+ if (dev->power.runtime_status != RPM_IDLE
+ || !dev->power.suspend_aborted)
+ goto repeat;
+ }
+
+ if (!pm_children_suspended(dev)) {
+ /*
+ * We can only suspend the device if all of its children have
+ * been suspended.
+ */
+ dev->power.runtime_status = RPM_ACTIVE;
+ error = -EBUSY;
+ goto out;
+ }
+
+ dev->power.runtime_status = RPM_SUSPENDING;
+ init_completion(&dev->power.work_done);
+
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+
+ if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_suspend)
+ error = dev->bus->pm->runtime_suspend(dev);
+ parent = dev->parent;
+
+ if (parent)
+ spin_lock_irqsave(&parent->power.lock, parflags);
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ switch (error) {
+ case 0:
+ /*
+ * Resume request might have been queued up in the meantime, in
+ * which case the RPM_WAKE bit is also set in runtime_status.
+ */
+ dev->power.runtime_status &= ~RPM_SUSPENDING;
+ 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) && parent) {
+ __pm_put_child(parent);
+
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+
+ if (!parent->power.child_count
+ && !parent->power.ignore_children)
+ pm_runtime_notify_idle(parent);
+
+ return 0;
+ }
+
+ out:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent)
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+
+ 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(suspend_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);
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ if (dev->power.runtime_status != RPM_ACTIVE
+ || atomic_read(&dev->power.resume_count) > 0)
+ goto out;
+
+ dev->power.runtime_status = RPM_IDLE;
+ dev->power.suspend_aborted = false;
+ queue_delayed_work(pm_wq, &dev->power.suspend_work, delay);
+
+ out:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+}
+EXPORT_SYMBOL_GPL(pm_request_suspend);
+
+/**
+ * __pm_runtime_resume - Run a device bus type's runtime_resume() callback.
+ * @dev: Device to resume.
+ * @get: If set, increment the device's resume counter.
+ * @sync: If unset, the funtion has been called via pm_wq.
+ *
+ * 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 get, bool sync)
+{
+ struct device *parent = dev->parent;
+ unsigned long parflags = 0, flags;
+ bool put_parent = false;
+ unsigned int status;
+ int error = -EINVAL;
+
+ might_sleep();
+
+ /*
+ * This makes concurrent __pm_runtime_suspend() and pm_request_suspend()
+ * started after us, or restarted, return immediately, so only the ones
+ * started before us can execute ->runtime_suspend().
+ */
+ pm_runtime_get(dev);
+
+ repeat:
+ if (parent)
+ spin_lock_irqsave(&parent->power.lock, parflags);
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ repeat_locked:
+ if (dev->power.runtime_status == RPM_ERROR) {
+ goto out;
+ } else if (dev->power.runtime_status == RPM_ACTIVE) {
+ error = 0;
+ goto out;
+ } else if (dev->power.runtime_status == RPM_IDLE
+ && !dev->power.suspend_aborted) {
+ /* Suspend request is pending, so cancel it. */
+ dev->power.suspend_aborted = true;
+
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent)
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+
+ cancel_delayed_work_sync(&dev->power.suspend_work);
+
+ if (parent)
+ spin_lock_irqsave(&parent->power.lock, parflags);
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ /* Repeat if anything has changed. */
+ if (dev->power.runtime_status != RPM_IDLE
+ || !dev->power.suspend_aborted)
+ goto repeat_locked;
+
+ /*
+ * Suspend request has been cancelled and there's nothing more
+ * to do. Clear the RPM_IDLE bit and return.
+ */
+ dev->power.runtime_status = RPM_ACTIVE;
+ error = 0;
+ goto out;
+ }
+
+ if (sync && (dev->power.runtime_status & RPM_WAKE)) {
+ /*
+ * Resume request is pending, so let it run, because it has to
+ * decrement the resume counter of the device.
+ */
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent)
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+
+ flush_work(&dev->power.resume_work);
+
+ goto repeat;
+ } else if (dev->power.runtime_status & RPM_SUSPENDING) {
+ /*
+ * Suspend is running in parallel with us. Wait for it to
+ * complete and repeat.
+ */
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent)
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+
+ wait_for_completion(&dev->power.work_done);
+
+ goto repeat;
+ } else if (!put_parent && dev->power.runtime_status == RPM_SUSPENDED
+ && parent && parent->power.runtime_status != RPM_ACTIVE) {
+ /* The parent has to be resumed before we can continue. */
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+
+ error = pm_runtime_resume_get(parent);
+ if (error)
+ return error;
+
+ put_parent = true;
+ error = -EINVAL;
+ goto repeat;
+ }
+
+ status = dev->power.runtime_status;
+ if (status == RPM_RESUMING)
+ goto unlock;
+
+ if (dev->power.runtime_status == RPM_SUSPENDED && parent)
+ __pm_get_child(parent);
+ dev->power.runtime_status = RPM_RESUMING;
+ init_completion(&dev->power.work_done);
+
+ unlock:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent) {
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+ /*
+ * We can decrement the parent's resume counter right now,
+ * because it can't be suspended anyway after the
+ * __pm_get_child() above.
+ */
+ if (put_parent)
+ pm_runtime_put(parent);
+ parent = NULL;
+ }
+
+ if (status == RPM_RESUMING) {
+ /*
+ * There's another resume running in parallel with us. Wait for
+ * it to complete and return.
+ */
+ wait_for_completion(&dev->power.work_done);
+
+ error = dev->power.runtime_error;
+ goto out_put;
+ }
+
+ if (dev->bus && dev->bus->pm && dev->bus->pm->runtime_resume)
+ error = dev->bus->pm->runtime_resume(dev);
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ dev->power.runtime_status = error ? RPM_ERROR : RPM_ACTIVE;
+ dev->power.runtime_error = error;
+ complete_all(&dev->power.work_done);
+
+ out:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent) {
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+ if (put_parent)
+ pm_runtime_put(parent);
+ }
+
+ out_put:
+ /* Allow suspends to run if we are supposed to. */
+ if (!get || error)
+ pm_runtime_put_notify(dev);
+
+ return error;
+}
+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)
+{
+ struct device *dev = resume_work_to_device(work);
+
+ __pm_runtime_resume(dev, false, false);
+ pm_runtime_put_notify(dev);
+}
+
+/**
+ * pm_cancel_suspend_work - Cancel a pending suspend request.
+ *
+ * Use @work to get the device object the work item has been scheduled for and
+ * cancel a pending suspend request for it.
+ */
+static void pm_cancel_suspend_work(struct work_struct *work)
+{
+ struct device *dev = resume_work_to_device(work);
+ unsigned long flags;
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ if (dev->power.runtime_status != RPM_IDLE
+ || !dev->power.suspend_aborted)
+ goto out;
+ /*
+ * Suspend request is pending, so cancel it. __pm_runtime_resume() and
+ * __pm_request_resume() will notice that suspend_aborted is true, so
+ * they will return immediately. Suspend requests and direct attempts
+ * to suspend are blocked by the increased resume counter.
+ */
+
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+
+ cancel_delayed_work_sync(&dev->power.suspend_work);
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ /* Clear the status if someone else hasn't done it already. */
+ if (dev->power.runtime_status == RPM_IDLE && dev->power.suspend_aborted)
+ dev->power.runtime_status = RPM_ACTIVE;
+
+ out:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+
+ pm_runtime_put_notify(dev);
+}
+
+/**
+ * __pm_request_resume - Schedule run-time resume of given device.
+ * @dev: Device to resume.
+ */
+int __pm_request_resume(struct device *dev, bool get)
+{
+ struct device *parent = dev->parent;
+ unsigned long parflags = 0, flags;
+ int error = 0;
+
+ if (parent)
+ spin_lock_irqsave(&parent->power.lock, parflags);
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ if (dev->power.runtime_status == RPM_ERROR) {
+ error = -EINVAL;
+ goto out;
+ }
+
+ if (get)
+ pm_runtime_get(dev);
+
+ if (dev->power.runtime_status == RPM_ACTIVE) {
+ error = -EBUSY;
+ goto out;
+ } else if (dev->power.runtime_status & (RPM_WAKE | RPM_RESUMING)) {
+ error = -EINPROGRESS;
+ goto out;
+ }
+
+ if (dev->power.runtime_status == RPM_IDLE) {
+ error = -EBUSY;
+
+ if (dev->power.suspend_aborted)
+ goto out;
+
+ /* Suspend request is pending. Queue a request to cancel it. */
+ dev->power.suspend_aborted = true;
+ INIT_WORK(&dev->power.resume_work, pm_cancel_suspend_work);
+ goto queue;
+ }
+
+ if (dev->power.runtime_status == RPM_SUSPENDED && parent)
+ __pm_get_child(parent);
+
+ /*
+ * 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.resume_work, pm_runtime_resume_work);
+
+ queue:
+ pm_runtime_get(dev);
+ queue_work(pm_wq, &dev->power.resume_work);
+
+ out:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent)
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+
+ return error;
+}
+EXPORT_SYMBOL_GPL(__pm_request_resume);
+
+/**
+ * __pm_runtime_clear_status - Change the run-time PM status of a device.
+ * @dev: Device to handle.
+ * @status: New value of the device's run-time PM status.
+ *
+ * Change the run-time PM status of the device to @status, which must be
+ * either RPM_ACTIVE or RPM_SUSPENDED, if its current value is equal to
+ * RPM_ERROR.
+ */
+void __pm_runtime_clear_status(struct device *dev, unsigned int status)
+{
+ struct device *parent = dev->parent;
+ unsigned long parflags = 0, flags;
+
+ if (status & ~RPM_SUSPENDED)
+ return;
+
+ if (parent)
+ spin_lock_irqsave(&parent->power.lock, parflags);
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ if (dev->power.runtime_status != RPM_ERROR)
+ goto out;
+
+ dev->power.runtime_status = status;
+ if (parent && status == RPM_SUSPENDED)
+ __pm_put_child(parent);
+
+ out:
+ spin_unlock_irqrestore(&dev->power.lock, flags);
+ if (parent)
+ spin_unlock_irqrestore(&parent->power.lock, parflags);
+}
+EXPORT_SYMBOL_GPL(__pm_runtime_clear_status);
+
+/**
+ * pm_runtime_init - Initialize run-time PM fields in given device object.
+ * @dev: Device object to initialize.
+ */
+void pm_runtime_init(struct device *dev)
+{
+ struct device *parent = dev->parent;
+
+ spin_lock_init(&dev->power.lock);
+
+ dev->power.runtime_status = RPM_ACTIVE;
+ atomic_set(&dev->power.resume_count, 1);
+ pm_suspend_ignore_children(dev, false);
+ dev->power.child_count = 0;
+ INIT_DELAYED_WORK(&dev->power.suspend_work, pm_runtime_suspend_work);
+
+ if (parent) {
+ unsigned long flags;
+
+ spin_lock_irqsave(&parent->power.lock, flags);
+ __pm_get_child(parent);
+ spin_unlock_irqrestore(&parent->power.lock, flags);
+ }
+}
+
+/**
+ * pm_runtime_close - Prepare for the removal of a device object.
+ * @dev: Device object being removed.
+ */
+void pm_runtime_close(struct device *dev)
+{
+ struct device *parent = dev->parent;
+ unsigned long flags;
+ unsigned int status;
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+
+ /* This makes __pm_runtime_suspend() return immediately. */
+ pm_runtime_get(dev);
+
+ while (dev->power.runtime_status & (RPM_SUSPENDING | RPM_RESUMING)) {
+ spin_unlock_irqrestore(&parent->power.lock, flags);
+
+ wait_for_completion(&dev->power.work_done);
+
+ spin_lock_irqsave(&dev->power.lock, flags);
+ }
+ status = dev->power.runtime_status;
+
+ /* This makes __pm_runtime_resume() return immediately. */
+ dev->power.runtime_status = RPM_ACTIVE;
+
+ spin_unlock_irqrestore(&parent->power.lock, flags);
+
+ if (status != RPM_SUSPENDED && parent) {
+ spin_lock_irqsave(&parent->power.lock, flags);
+ __pm_put_child(parent);
+ spin_unlock_irqrestore(&parent->power.lock, flags);
+ }
+}
Index: linux-2.6/include/linux/pm_runtime.h
===================================================================
--- /dev/null
+++ linux-2.6/include/linux/pm_runtime.h
@@ -0,0 +1,148 @@
+/*
+ * 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_close(struct device *dev);
+extern void pm_runtime_put_notify(struct device *dev);
+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 get, bool sync);
+extern int __pm_request_resume(struct device *dev, bool);
+extern void __pm_runtime_clear_status(struct device *dev, unsigned int status);
+
+static inline struct device *suspend_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, suspend_work);
+ return container_of(dpi, struct device, power);
+}
+
+static inline struct device *resume_work_to_device(struct work_struct *work)
+{
+ struct dev_pm_info *dpi;
+
+ dpi = container_of(work, struct dev_pm_info, resume_work);
+ return container_of(dpi, struct device, power);
+}
+
+static inline void pm_runtime_get(struct device *dev)
+{
+ atomic_inc(&dev->power.resume_count);
+}
+
+static inline void pm_runtime_put(struct device *dev)
+{
+ if (!atomic_add_unless(&dev->power.resume_count, -1, 0))
+ dev_warn(dev, "Excessive %s!\n", __FUNCTION__);
+}
+
+static inline bool pm_children_suspended(struct device *dev)
+{
+ return dev->power.ignore_children || !dev->power.child_count;
+}
+
+static inline bool pm_suspend_possible(struct device *dev)
+{
+ return pm_children_suspended(dev)
+ && !atomic_read(&dev->power.resume_count)
+ && !(dev->power.runtime_status & RPM_WAKE);
+}
+
+static inline void pm_suspend_ignore_children(struct device *dev, bool enable)
+{
+ dev->power.ignore_children = enable;
+}
+
+#else /* !CONFIG_PM_RUNTIME */
+
+static inline void pm_runtime_init(struct device *dev) {}
+static inline void pm_runtime_close(struct device *dev) {}
+static inline void pm_runtime_put_notify(struct device *dev) {}
+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 get, bool sync)
+{
+ return -ENOSYS;
+}
+static inline int __pm_request_resume(struct device *dev, bool get)
+{
+ return -ENOSYS;
+}
+static inline void __pm_runtime_clear_status(struct device *dev,
+ unsigned int status) {}
+
+static inline void pm_runtime_get(struct device *dev) {}
+static inline bool pm_children_suspended(struct device *dev) { return false; }
+static inline bool pm_suspend_possible(struct device *dev) { return false; }
+static inline void pm_suspend_ignore_children(struct device *dev, bool en) {}
+static inline void pm_runtime_put(struct device *dev) {}
+
+#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, true);
+}
+
+static inline int pm_runtime_resume_get(struct device *dev)
+{
+ return __pm_runtime_resume(dev, true, true);
+}
+
+static inline int pm_request_resume(struct device *dev)
+{
+ return __pm_request_resume(dev, false);
+}
+
+static inline int pm_request_resume_get(struct device *dev)
+{
+ return __pm_request_resume(dev, true);
+}
+
+static inline void pm_runtime_clear_active(struct device *dev)
+{
+ __pm_runtime_clear_status(dev, RPM_ACTIVE);
+}
+
+static inline void pm_runtime_clear_suspended(struct device *dev)
+{
+ __pm_runtime_clear_status(dev, RPM_SUSPENDED);
+}
+
+static inline void pm_runtime_enable(struct device *dev)
+{
+ pm_runtime_put(dev);
+}
+
+static inline void pm_runtime_disable(struct device *dev)
+{
+ pm_runtime_get(dev);
+ pm_runtime_resume(dev);
+}
+
+#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);
}

@@ -104,6 +106,7 @@ void device_pm_remove(struct device *dev
kobject_name(&dev->kobj));
mutex_lock(&dpm_list_mtx);
list_del_init(&dev->power.entry);
+ pm_runtime_close(dev);
mutex_unlock(&dpm_list_mtx);
}

@@ -507,6 +510,7 @@ 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 +757,7 @@ 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 +765,7 @@ 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 +1,416 @@
+Run-time Power Management Framework for I/O Devices
+
+(C) 2009 Rafael J. Wysocki <rjw@sisk.pl>, Novell Inc.
+
+1. Introduction
+
+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 of 'struct dev_pm_info', the helper functions
+using them and the run-time PM callbacks present 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_close(struct device *dev);
+
+* void pm_runtime_get(struct device *dev);
+* void pm_runtime_put(struct device *dev);
+* void pm_runtime_put_notify(struct device *dev);
+* int pm_runtime_suspend(struct device *dev);
+* void pm_request_suspend(struct device *dev, unsigned int msec);
+* int pm_runtime_resume(struct device *dev);
+* int pm_runtime_resume_get(struct device *dev);
+* void pm_request_resume(struct device *dev);
+
+* bool pm_suspend_possible(struct device *dev);
+
+* void pm_runtime_enable(struct device *dev);
+* void pm_runtime_disable(struct device *dev);
+
+* void pm_suspend_ignore_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
+a device object. It is called during the initialization of the device object,
+in drivers/base/power/main.c:device_pm_add().
+
+pm_runtime_close() disables the run-time PM of a device and updates the 'power'
+member of its parent's device object to take the removal of the device into
+account. It is called during the destruction of the device object, in
+drivers/base/power/main.c:device_pm_remove().
+
+pm_runtime_suspend(), pm_request_suspend(), pm_runtime_resume(),
+pm_runtime_resume_get(), pm_request_resume(), and pm_request_resume_get()
+use the 'power.runtime_status', 'power.resume_count', 'power.suspend_aborted',
+and 'power.child_count' fields of 'struct device' for mutual cooperation. In
+what follows the 'power.runtime_status', 'power.resume_count', and
+'power.child_count' fields are referred to as the device's run-time PM status,
+the device's resume counter, and the counter of unsuspended children of the
+device, respectively. They are set to RPM_ACTIVE, 1 and 0, respectively, by
+pm_runtime_init().
+
+pm_runtime_get() is used to increase the device's resume counter by 1. If the
+resume counter of the device is greater than 0, it will cause the PM core to
+refuse to suspend the device or to queue up a suspend request for it. 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. It is valid to call this function from
+interrupt context.
+
+pm_runtime_put() is used to decrease the device's resume counter by 1 if it's
+greater than 0. pm_runtime_put_notify() additionally checks if the device's
+resume counter is equal to zero (after it's just been decreased) and if all
+children of the device are suspended (or it has the 'power.ignore_children' flag
+set). If that is the case, the ->runtime_idle() callback provided by the
+device's bus type is executed for it.
+
+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, but internally
+it calls __pm_runtime_suspend() that is also used for asynchronous suspending of
+devices (i.e. to complete requests queued up by pm_request_suspend()) and works
+as follows.
+
+ * 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's resume counter is greater than 0 or the function has been
+ called via pm_wq as a result of a cancelled suspend request (the RPM_IDLE
+ bit is set in the device's run-time PM status field and its
+ 'power.suspend_aborted' flag is set), -EAGAIN is returned.
+
+ * If the device is suspending (i.e. the RPM_SUSPENDING bit is set in its
+ run-time PM status field), 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 result
+ returned by it.
+
+ * If the device has a pending suspend request (i.e. the RPM_IDLE bit is set in
+ its run-time PM status) and the function hasn't been called as a result of
+ that request, it cancels the request (synchronously) and restarts itself if
+ a concurrent suspend or resume is running in parallel with it or a resume
+ request has just been queued up.
+
+ * If the children of the device are not suspended and the
+ 'power.ignore_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, or a pending suspend request has been
+successfully cancelled, 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
+entirely 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_SUSPENDING bit is cleared and the
+ RPM_SUSPENDED bit is set 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 entirely 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 and there's no resume request pending for the device
+ (i.e. the RPM_WAKE flag is not set in its run-time PM status field), and the
+ device has a parent, the parent's counter of unsuspended children (i.e. the
+ 'power.child_count' field) is decremented. If that counter turns out to be
+ equal to zero (i.e. the device was the last unsuspended child of its parent)
+ and the parent's 'power.ignore_children' flag is unset, and the parent's
+ resume counter is equal to 0, its bus type's ->runtime_idle() callback is
+ executed 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, which makes the PM core 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 pm_runtime_clear_active() or pm_runtime_clear_suspended().
+
+Finally, pm_runtime_suspend() returns the result 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_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
+or its resume counter is greater than 0 (i.e. the device is not active from the
+PM core standpoint), the function 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_resume() and pm_runtime_resume_get() 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 directly by a bus type or device driver and
+the difference between them is that pm_runtime_resume_get() leaves the device's
+resume counter incremented. Internally, however, they both call
+__pm_runtime_resume() that is also used for asynchronous resuming of devices
+(i.e. to complete requests queued up by pm_request_resume() or
+pm_request_resume_get()). It first increments the device's resume counter to
+prevent new suspend requests from being queued up and to make subsequent
+attempts to suspend the device fail. The device's resume counter will be
+decremented on return, unless success is about to be returned and the function
+is requested to hold a reference to the device (i.e. in the
+pm_runtime_resume_get() case).
+
+After incrementing the device's run-time PM counter __pm_runtime_resume()
+proceeds as follows.
+
+ * If the device is active (i.e. all of the bits in its run-time PM status are
+ unset), success is returned.
+
+ * If there's a suspend request pending for the device (i.e. the RPM_IDLE bit
+ is set in the device's run-time PM status field), the
+ 'power.suspend_aborted' flag is set for the device and the request is
+ cancelled (synchronously). Then, the function restarts itself if the
+ device's RPM_IDLE bit was cleared or the 'power.suspend_aborted' flag was
+ unset in the meantime by a concurrent thread. Otherwise, the device's
+ run-time PM status is cleared to RPM_ACTIVE and the function returns
+ success.
+
+ * If the device has a pending resume request (i.e. the RPM_WAKE bit is set in
+ its run-time PM status field), but the function hasn't been called as a
+ result of that request, the request is waited for to complete and the
+ function restarts itself.
+
+ * 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 and doesn't have a pending resume request (i.e.
+ its run-time PM status is RPM_SUSPENDED), and it has a parent that is not
+ active (i.e. the parent's run-time PM status is not RPM_ACTIVE),
+ pm_runtime_resume_get() is called (recursively) for the parent. If the
+ parent's resume is successful, the function notes that the parent's resume
+ counter will have to be decremented and restarts itself. Otherwise, it
+ returns the error code returned by the instance of pm_runtime_resume_get()
+ handling the device's parent.
+
+ * 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 function checks if the device's run-time PM
+status is RPM_SUSPENDED, which means that the device doesn't have a resume
+request pending, and if it has a parent. If that is the case, the parent's
+counter of unsuspended children is increased. Next, the device's run-time PM
+status is set to RPM_RESUMING and its bus type's ->runtime_resume() callback is
+executed. This callback is entirely 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
+ 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
+ success, the device _must_ be able to carry out I/O operations as needed).
+
+ * If an error code is returned, the device's run-time PM status is set to
+ RPM_ERROR, which makes the PM core refuse to carry out any run-time PM
+ operations for the device 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(). Thus, it is strongly recommended that bus
+ types' ->runtime_resume() callbacks only return error codes in fatal error
+ conditions, when it is impossible to bring the device back to the
+ operational state by any available means. Inability to wake up a suspended
+ device usually means a service loss and it may very well result in a data
+ loss to the user, so it _must_ be regarded as a severe problem and avoided
+ if at all possible.
+
+Finally, __pm_runtime_resume() returns the result returned by the device bus
+type's ->runtime_resume() callback. The device's resume counter is decremented
+right before the function returns, unless success is about to be returned and
+the function is requested to hold a reference to the device (i.e. in the
+pm_runtime_resume_get() case). 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_request_resume() and pm_request_resume_get() 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_get() leaves the
+device's resume counter incremented, so the device cannot be suspended by
+__pm_runtime_suspend() after it has run. Internally, they both call
+__pm_request_resume() which works as follows.
+
+* If the function is requested to take a reference to the device (i.e. in the
+ pm_request_resume_get() case), the device's resume counter is incremented.
+
+* If the run-time PM status of the device is RPM_ACTIVE, -EBUSY is returned.
+
+* If the device is resuming or has a resume request pending (i.e. at least one
+ of the RPM_WAKE and RPM_RESUMING bits is set in the device's run-time PM
+ status field), -EINPROGRESS is returned.
+
+* If the device's run-time status is RPM_IDLE (i.e. a suspend request is pending
+ for it) and the 'power.suspend_aborted' flag is set (i.e. the pending request
+ is being cancelled), -EBUSY is returned.
+
+* If the device's run-time status is RPM_IDLE (i.e. a suspend request is pending
+ for it) and the 'power.suspend_aborted' flag is not set, the device's
+ 'power.suspend_aborted' flag is set, a request to cancel the pending suspend
+ request is queued up and the device's resume counter is increased (it will be
+ decreased by the work function when it's done its job). Finally, -EBUSY is
+ returned.
+
+If none of the above happens, the function checks if the device's run-time PM
+status is RPM_SUSPENDED and if it has a parent, in which case the parent's
+counter of unsuspended children is incremented. Next, the function grabs a
+reference to the device by increasing its resume counter (this reference is
+going to be dropped automatically after the __pm_runtime_resume() handling the
+request has run), 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.
+Finally, the function returns 0, which means that the resume request has been
+successfully queued up. It is valid to call this function from interrupt
+context.
+
+Note that it usually is _not_ safe to access the device for I/O purposes
+immediately after __pm_request_resume() has returned, unless the returned result
+is -EBUSY, which means that it wasn't necessary to resume the device.
+
+Note also that only one suspend request or one resume request may be queued up
+at any given moment. Moreover, a resume request cannot be queued up along with
+a suspend request. Still, if it's necessary to queue up a request to cancel a
+pending suspend request, these two requests will be present in pm_wq at the
+same time. In that case, regardless of which request is attempted to complete
+first, the device's run-time PM status will be set to RPM_ACTIVE as a final
+result.
+
+pm_suspend_possible() is used to check if the device may be suspended at this
+particular moment. It checks the device's resume counter and the counter of
+unsuspended children. It returns 'false' if any of these counters is greater
+than 0 or 'true' otherwise.
+
+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
+decrementing and incrementing, respectively, the device's resume counter, which
+also is done by pm_runtime_get() and pm_runtime_put(). However,
+pm_runtime_enable() doesn't notify the device's bus type of its resume counter
+reaching 0 and pm_runtime_disable() additionally calls pm_runtime_resume() for
+the device after incrementing its resume counter to ensure that it will not be
+suspended while its run-time PM is disabled. 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 work for that device. The initial value of the device's
+resume counter, as set by pm_runtime_init(), is 1 (i.e. the device's run-time PM
+is initially disabled).
+
+pm_runtime_disable() and pm_runtime_enable() are used by the device core to
+disable the run-time power management of devices 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_suspend_ignore_children() is used to set or unset the
+'power.ignore_children' flag in 'struct device'. If the 'enabled'
+argument is 'true', the field is set to 1, and if 'enable' is 'false', the field
+is set to 0. The default value of 'power.ignore_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. It is valid to call this function from
+interrupt context.
+
+pm_runtime_clear_suspended() is used to change the device's run-time PM status
+field from RPM_ERROR to RPM_SUSPENDED. If the device has a parent, it the
+function additionally decrements the parent's counter of unsuspended children,
+although the parent's bus type is not notified if the counter becomes 0. It is
+valid to call this function from interrupt context.
+
+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.