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diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
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+			Power Management for USB
+
+		 Alan Stern <stern@rowland.harvard.edu>
+
+			    October 28, 2010
+
+
+
+	What is Power Management?
+	-------------------------
+
+Power Management (PM) is the practice of saving energy by suspending
+parts of a computer system when they aren't being used.  While a
+component is "suspended" it is in a nonfunctional low-power state; it
+might even be turned off completely.  A suspended component can be
+"resumed" (returned to a functional full-power state) when the kernel
+needs to use it.  (There also are forms of PM in which components are
+placed in a less functional but still usable state instead of being
+suspended; an example would be reducing the CPU's clock rate.  This
+document will not discuss those other forms.)
+
+When the parts being suspended include the CPU and most of the rest of
+the system, we speak of it as a "system suspend".  When a particular
+device is turned off while the system as a whole remains running, we
+call it a "dynamic suspend" (also known as a "runtime suspend" or
+"selective suspend").  This document concentrates mostly on how
+dynamic PM is implemented in the USB subsystem, although system PM is
+covered to some extent (see Documentation/power/*.txt for more
+information about system PM).
+
+Note: Dynamic PM support for USB is present only if the kernel was
+built with CONFIG_USB_SUSPEND enabled (which depends on
+CONFIG_PM_RUNTIME).  System PM support is present only if the kernel
+was built with CONFIG_SUSPEND or CONFIG_HIBERNATION enabled.
+
+
+	What is Remote Wakeup?
+	----------------------
+
+When a device has been suspended, it generally doesn't resume until
+the computer tells it to.  Likewise, if the entire computer has been
+suspended, it generally doesn't resume until the user tells it to, say
+by pressing a power button or opening the cover.
+
+However some devices have the capability of resuming by themselves, or
+asking the kernel to resume them, or even telling the entire computer
+to resume.  This capability goes by several names such as "Wake On
+LAN"; we will refer to it generically as "remote wakeup".  When a
+device is enabled for remote wakeup and it is suspended, it may resume
+itself (or send a request to be resumed) in response to some external
+event.  Examples include a suspended keyboard resuming when a key is
+pressed, or a suspended USB hub resuming when a device is plugged in.
+
+
+	When is a USB device idle?
+	--------------------------
+
+A device is idle whenever the kernel thinks it's not busy doing
+anything important and thus is a candidate for being suspended.  The
+exact definition depends on the device's driver; drivers are allowed
+to declare that a device isn't idle even when there's no actual
+communication taking place.  (For example, a hub isn't considered idle
+unless all the devices plugged into that hub are already suspended.)
+In addition, a device isn't considered idle so long as a program keeps
+its usbfs file open, whether or not any I/O is going on.
+
+If a USB device has no driver, its usbfs file isn't open, and it isn't
+being accessed through sysfs, then it definitely is idle.
+
+
+	Forms of dynamic PM
+	-------------------
+
+Dynamic suspends occur when the kernel decides to suspend an idle
+device.  This is called "autosuspend" for short.  In general, a device
+won't be autosuspended unless it has been idle for some minimum period
+of time, the so-called idle-delay time.
+
+Of course, nothing the kernel does on its own initiative should
+prevent the computer or its devices from working properly.  If a
+device has been autosuspended and a program tries to use it, the
+kernel will automatically resume the device (autoresume).  For the
+same reason, an autosuspended device will usually have remote wakeup
+enabled, if the device supports remote wakeup.
+
+It is worth mentioning that many USB drivers don't support
+autosuspend.  In fact, at the time of this writing (Linux 2.6.23) the
+only drivers which do support it are the hub driver, kaweth, asix,
+usblp, usblcd, and usb-skeleton (which doesn't count).  If a
+non-supporting driver is bound to a device, the device won't be
+autosuspended.  In effect, the kernel pretends the device is never
+idle.
+
+We can categorize power management events in two broad classes:
+external and internal.  External events are those triggered by some
+agent outside the USB stack: system suspend/resume (triggered by
+userspace), manual dynamic resume (also triggered by userspace), and
+remote wakeup (triggered by the device).  Internal events are those
+triggered within the USB stack: autosuspend and autoresume.  Note that
+all dynamic suspend events are internal; external agents are not
+allowed to issue dynamic suspends.
+
+
+	The user interface for dynamic PM
+	---------------------------------
+
+The user interface for controlling dynamic PM is located in the power/
+subdirectory of each USB device's sysfs directory, that is, in
+/sys/bus/usb/devices/.../power/ where "..." is the device's ID.  The
+relevant attribute files are: wakeup, control, and
+autosuspend_delay_ms.  (There may also be a file named "level"; this
+file was deprecated as of the 2.6.35 kernel and replaced by the
+"control" file.  In 2.6.38 the "autosuspend" file will be deprecated
+and replaced by the "autosuspend_delay_ms" file.  The only difference
+is that the newer file expresses the delay in milliseconds whereas the
+older file uses seconds.  Confusingly, both files are present in 2.6.37
+but only "autosuspend" works.)
+
+	power/wakeup
+
+		This file is empty if the device does not support
+		remote wakeup.  Otherwise the file contains either the
+		word "enabled" or the word "disabled", and you can
+		write those words to the file.  The setting determines
+		whether or not remote wakeup will be enabled when the
+		device is next suspended.  (If the setting is changed
+		while the device is suspended, the change won't take
+		effect until the following suspend.)
+
+	power/control
+
+		This file contains one of two words: "on" or "auto".
+		You can write those words to the file to change the
+		device's setting.
+
+		"on" means that the device should be resumed and
+		autosuspend is not allowed.  (Of course, system
+		suspends are still allowed.)
+
+		"auto" is the normal state in which the kernel is
+		allowed to autosuspend and autoresume the device.
+
+		(In kernels up to 2.6.32, you could also specify
+		"suspend", meaning that the device should remain
+		suspended and autoresume was not allowed.  This
+		setting is no longer supported.)
+
+	power/autosuspend_delay_ms
+
+		This file contains an integer value, which is the
+		number of milliseconds the device should remain idle
+		before the kernel will autosuspend it (the idle-delay
+		time).  The default is 2000.  0 means to autosuspend
+		as soon as the device becomes idle, and negative
+		values mean never to autosuspend.  You can write a
+		number to the file to change the autosuspend
+		idle-delay time.
+
+Writing "-1" to power/autosuspend_delay_ms and writing "on" to
+power/control do essentially the same thing -- they both prevent the
+device from being autosuspended.  Yes, this is a redundancy in the
+API.
+
+(In 2.6.21 writing "0" to power/autosuspend would prevent the device
+from being autosuspended; the behavior was changed in 2.6.22.  The
+power/autosuspend attribute did not exist prior to 2.6.21, and the
+power/level attribute did not exist prior to 2.6.22.  power/control
+was added in 2.6.34, and power/autosuspend_delay_ms was added in
+2.6.37 but did not become functional until 2.6.38.)
+
+
+	Changing the default idle-delay time
+	------------------------------------
+
+The default autosuspend idle-delay time (in seconds) is controlled by
+a module parameter in usbcore.  You can specify the value when usbcore
+is loaded.  For example, to set it to 5 seconds instead of 2 you would
+do:
+
+	modprobe usbcore autosuspend=5
+
+Equivalently, you could add to a configuration file in /etc/modprobe.d
+a line saying:
+
+	options usbcore autosuspend=5
+
+Some distributions load the usbcore module very early during the boot
+process, by means of a program or script running from an initramfs
+image.  To alter the parameter value you would have to rebuild that
+image.
+
+If usbcore is compiled into the kernel rather than built as a loadable
+module, you can add
+
+	usbcore.autosuspend=5
+
+to the kernel's boot command line.
+
+Finally, the parameter value can be changed while the system is
+running.  If you do:
+
+	echo 5 >/sys/module/usbcore/parameters/autosuspend
+
+then each new USB device will have its autosuspend idle-delay
+initialized to 5.  (The idle-delay values for already existing devices
+will not be affected.)
+
+Setting the initial default idle-delay to -1 will prevent any
+autosuspend of any USB device.  This is a simple alternative to
+disabling CONFIG_USB_SUSPEND and rebuilding the kernel, and it has the
+added benefit of allowing you to enable autosuspend for selected
+devices.
+
+
+	Warnings
+	--------
+
+The USB specification states that all USB devices must support power
+management.  Nevertheless, the sad fact is that many devices do not
+support it very well.  You can suspend them all right, but when you
+try to resume them they disconnect themselves from the USB bus or
+they stop working entirely.  This seems to be especially prevalent
+among printers and scanners, but plenty of other types of device have
+the same deficiency.
+
+For this reason, by default the kernel disables autosuspend (the
+power/control attribute is initialized to "on") for all devices other
+than hubs.  Hubs, at least, appear to be reasonably well-behaved in
+this regard.
+
+(In 2.6.21 and 2.6.22 this wasn't the case.  Autosuspend was enabled
+by default for almost all USB devices.  A number of people experienced
+problems as a result.)
+
+This means that non-hub devices won't be autosuspended unless the user
+or a program explicitly enables it.  As of this writing there aren't
+any widespread programs which will do this; we hope that in the near
+future device managers such as HAL will take on this added
+responsibility.  In the meantime you can always carry out the
+necessary operations by hand or add them to a udev script.  You can
+also change the idle-delay time; 2 seconds is not the best choice for
+every device.
+
+If a driver knows that its device has proper suspend/resume support,
+it can enable autosuspend all by itself.  For example, the video
+driver for a laptop's webcam might do this (in recent kernels they
+do), since these devices are rarely used and so should normally be
+autosuspended.
+
+Sometimes it turns out that even when a device does work okay with
+autosuspend there are still problems.  For example, the usbhid driver,
+which manages keyboards and mice, has autosuspend support.  Tests with
+a number of keyboards show that typing on a suspended keyboard, while
+causing the keyboard to do a remote wakeup all right, will nonetheless
+frequently result in lost keystrokes.  Tests with mice show that some
+of them will issue a remote-wakeup request in response to button
+presses but not to motion, and some in response to neither.
+
+The kernel will not prevent you from enabling autosuspend on devices
+that can't handle it.  It is even possible in theory to damage a
+device by suspending it at the wrong time.  (Highly unlikely, but
+possible.)  Take care.
+
+
+	The driver interface for Power Management
+	-----------------------------------------
+
+The requirements for a USB driver to support external power management
+are pretty modest; the driver need only define
+
+	.suspend
+	.resume
+	.reset_resume
+
+methods in its usb_driver structure, and the reset_resume method is
+optional.  The methods' jobs are quite simple:
+
+	The suspend method is called to warn the driver that the
+	device is going to be suspended.  If the driver returns a
+	negative error code, the suspend will be aborted.  Normally
+	the driver will return 0, in which case it must cancel all
+	outstanding URBs (usb_kill_urb()) and not submit any more.
+
+	The resume method is called to tell the driver that the
+	device has been resumed and the driver can return to normal
+	operation.  URBs may once more be submitted.
+
+	The reset_resume method is called to tell the driver that
+	the device has been resumed and it also has been reset.
+	The driver should redo any necessary device initialization,
+	since the device has probably lost most or all of its state
+	(although the interfaces will be in the same altsettings as
+	before the suspend).
+
+If the device is disconnected or powered down while it is suspended,
+the disconnect method will be called instead of the resume or
+reset_resume method.  This is also quite likely to happen when
+waking up from hibernation, as many systems do not maintain suspend
+current to the USB host controllers during hibernation.  (It's
+possible to work around the hibernation-forces-disconnect problem by
+using the USB Persist facility.)
+
+The reset_resume method is used by the USB Persist facility (see
+Documentation/usb/persist.txt) and it can also be used under certain
+circumstances when CONFIG_USB_PERSIST is not enabled.  Currently, if a
+device is reset during a resume and the driver does not have a
+reset_resume method, the driver won't receive any notification about
+the resume.  Later kernels will call the driver's disconnect method;
+2.6.23 doesn't do this.
+
+USB drivers are bound to interfaces, so their suspend and resume
+methods get called when the interfaces are suspended or resumed.  In
+principle one might want to suspend some interfaces on a device (i.e.,
+force the drivers for those interface to stop all activity) without
+suspending the other interfaces.  The USB core doesn't allow this; all
+interfaces are suspended when the device itself is suspended and all
+interfaces are resumed when the device is resumed.  It isn't possible
+to suspend or resume some but not all of a device's interfaces.  The
+closest you can come is to unbind the interfaces' drivers.
+
+
+	The driver interface for autosuspend and autoresume
+	---------------------------------------------------
+
+To support autosuspend and autoresume, a driver should implement all
+three of the methods listed above.  In addition, a driver indicates
+that it supports autosuspend by setting the .supports_autosuspend flag
+in its usb_driver structure.  It is then responsible for informing the
+USB core whenever one of its interfaces becomes busy or idle.  The
+driver does so by calling these six functions:
+
+	int  usb_autopm_get_interface(struct usb_interface *intf);
+	void usb_autopm_put_interface(struct usb_interface *intf);
+	int  usb_autopm_get_interface_async(struct usb_interface *intf);
+	void usb_autopm_put_interface_async(struct usb_interface *intf);
+	void usb_autopm_get_interface_no_resume(struct usb_interface *intf);
+	void usb_autopm_put_interface_no_suspend(struct usb_interface *intf);
+
+The functions work by maintaining a usage counter in the
+usb_interface's embedded device structure.  When the counter is > 0
+then the interface is deemed to be busy, and the kernel will not
+autosuspend the interface's device.  When the usage counter is = 0
+then the interface is considered to be idle, and the kernel may
+autosuspend the device.
+
+Drivers need not be concerned about balancing changes to the usage
+counter; the USB core will undo any remaining "get"s when a driver
+is unbound from its interface.  As a corollary, drivers must not call
+any of the usb_autopm_* functions after their disconnect() routine has
+returned.
+
+Drivers using the async routines are responsible for their own
+synchronization and mutual exclusion.
+
+	usb_autopm_get_interface() increments the usage counter and
+	does an autoresume if the device is suspended.  If the
+	autoresume fails, the counter is decremented back.
+
+	usb_autopm_put_interface() decrements the usage counter and
+	attempts an autosuspend if the new value is = 0.
+
+	usb_autopm_get_interface_async() and
+	usb_autopm_put_interface_async() do almost the same things as
+	their non-async counterparts.  The big difference is that they
+	use a workqueue to do the resume or suspend part of their
+	jobs.  As a result they can be called in an atomic context,
+	such as an URB's completion handler, but when they return the
+	device will generally not yet be in the desired state.
+
+	usb_autopm_get_interface_no_resume() and
+	usb_autopm_put_interface_no_suspend() merely increment or
+	decrement the usage counter; they do not attempt to carry out
+	an autoresume or an autosuspend.  Hence they can be called in
+	an atomic context.
+
+The simplest usage pattern is that a driver calls
+usb_autopm_get_interface() in its open routine and
+usb_autopm_put_interface() in its close or release routine.  But other
+patterns are possible.
+
+The autosuspend attempts mentioned above will often fail for one
+reason or another.  For example, the power/control attribute might be
+set to "on", or another interface in the same device might not be
+idle.  This is perfectly normal.  If the reason for failure was that
+the device hasn't been idle for long enough, a timer is scheduled to
+carry out the operation automatically when the autosuspend idle-delay
+has expired.
+
+Autoresume attempts also can fail, although failure would mean that
+the device is no longer present or operating properly.  Unlike
+autosuspend, there's no idle-delay for an autoresume.
+
+
+	Other parts of the driver interface
+	-----------------------------------
+
+Drivers can enable autosuspend for their devices by calling
+
+	usb_enable_autosuspend(struct usb_device *udev);
+
+in their probe() routine, if they know that the device is capable of
+suspending and resuming correctly.  This is exactly equivalent to
+writing "auto" to the device's power/control attribute.  Likewise,
+drivers can disable autosuspend by calling
+
+	usb_disable_autosuspend(struct usb_device *udev);
+
+This is exactly the same as writing "on" to the power/control attribute.
+
+Sometimes a driver needs to make sure that remote wakeup is enabled
+during autosuspend.  For example, there's not much point
+autosuspending a keyboard if the user can't cause the keyboard to do a
+remote wakeup by typing on it.  If the driver sets
+intf->needs_remote_wakeup to 1, the kernel won't autosuspend the
+device if remote wakeup isn't available.  (If the device is already
+autosuspended, though, setting this flag won't cause the kernel to
+autoresume it.  Normally a driver would set this flag in its probe
+method, at which time the device is guaranteed not to be
+autosuspended.)
+
+If a driver does its I/O asynchronously in interrupt context, it
+should call usb_autopm_get_interface_async() before starting output and
+usb_autopm_put_interface_async() when the output queue drains.  When
+it receives an input event, it should call
+
+	usb_mark_last_busy(struct usb_device *udev);
+
+in the event handler.  This tells the PM core that the device was just
+busy and therefore the next autosuspend idle-delay expiration should
+be pushed back.  Many of the usb_autopm_* routines also make this call,
+so drivers need to worry only when interrupt-driven input arrives.
+
+Asynchronous operation is always subject to races.  For example, a
+driver may call the usb_autopm_get_interface_async() routine at a time
+when the core has just finished deciding the device has been idle for
+long enough but not yet gotten around to calling the driver's suspend
+method.  The suspend method must be responsible for synchronizing with
+the I/O request routine and the URB completion handler; it should
+cause autosuspends to fail with -EBUSY if the driver needs to use the
+device.
+
+External suspend calls should never be allowed to fail in this way,
+only autosuspend calls.  The driver can tell them apart by applying
+the PMSG_IS_AUTO() macro to the message argument to the suspend
+method; it will return True for internal PM events (autosuspend) and
+False for external PM events.
+
+
+	Mutual exclusion
+	----------------
+
+For external events -- but not necessarily for autosuspend or
+autoresume -- the device semaphore (udev->dev.sem) will be held when a
+suspend or resume method is called.  This implies that external
+suspend/resume events are mutually exclusive with calls to probe,
+disconnect, pre_reset, and post_reset; the USB core guarantees that
+this is true of autosuspend/autoresume events as well.
+
+If a driver wants to block all suspend/resume calls during some
+critical section, the best way is to lock the device and call
+usb_autopm_get_interface() (and do the reverse at the end of the
+critical section).  Holding the device semaphore will block all
+external PM calls, and the usb_autopm_get_interface() will prevent any
+internal PM calls, even if it fails.  (Exercise: Why?)
+
+
+	Interaction between dynamic PM and system PM
+	--------------------------------------------
+
+Dynamic power management and system power management can interact in
+a couple of ways.
+
+Firstly, a device may already be autosuspended when a system suspend
+occurs.  Since system suspends are supposed to be as transparent as
+possible, the device should remain suspended following the system
+resume.  But this theory may not work out well in practice; over time
+the kernel's behavior in this regard has changed.  As of 2.6.37 the
+policy is to resume all devices during a system resume and let them
+handle their own runtime suspends afterward.
+
+Secondly, a dynamic power-management event may occur as a system
+suspend is underway.  The window for this is short, since system
+suspends don't take long (a few seconds usually), but it can happen.
+For example, a suspended device may send a remote-wakeup signal while
+the system is suspending.  The remote wakeup may succeed, which would
+cause the system suspend to abort.  If the remote wakeup doesn't
+succeed, it may still remain active and thus cause the system to
+resume as soon as the system suspend is complete.  Or the remote
+wakeup may fail and get lost.  Which outcome occurs depends on timing
+and on the hardware and firmware design.
+
+
+	xHCI hardware link PM
+	---------------------
+
+xHCI host controller provides hardware link power management to usb2.0
+(xHCI 1.0 feature) and usb3.0 devices which support link PM. By
+enabling hardware LPM, the host can automatically put the device into
+lower power state(L1 for usb2.0 devices, or U1/U2 for usb3.0 devices),
+which state device can enter and resume very quickly.
+
+The user interface for controlling USB2 hardware LPM is located in the
+power/ subdirectory of each USB device's sysfs directory, that is, in
+/sys/bus/usb/devices/.../power/ where "..." is the device's ID. The
+relevant attribute files is usb2_hardware_lpm.
+
+	power/usb2_hardware_lpm
+
+		When a USB2 device which support LPM is plugged to a
+		xHCI host root hub which support software LPM, the
+		host will run a software LPM test for it; if the device
+		enters L1 state and resume successfully and the host
+		supports USB2 hardware LPM, this file will show up and
+		driver will enable hardware LPM	for the device. You
+		can write y/Y/1 or n/N/0 to the file to	enable/disable
+		USB2 hardware LPM manually. This is for	test purpose mainly.