USB: convert to the runtime PM framework

This patch (as1329) converts the USB stack over to the PM core's
runtime PM framework.  This involves numerous changes throughout
usbcore, especially to hub.c and driver.c.  Perhaps the most notable
change is that CONFIG_USB_SUSPEND now depends on CONFIG_PM_RUNTIME
instead of CONFIG_PM.

Several fields in the usb_device and usb_interface structures are no
longer needed.  Some code which used to depend on CONFIG_USB_PM now
depends on CONFIG_USB_SUSPEND (requiring some rearrangement of header
files).

The only visible change in behavior should be that following a system
sleep (resume from RAM or resume from hibernation), autosuspended USB
devices will be resumed just like everything else.  They won't remain
suspended.  But if they aren't in use then they will naturally
autosuspend again in a few seconds.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 77 insertions, 140 deletions

diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index e3fa189c257..2790ad48cfc 100644
--- a/Documentation/usb/power-management.txt
+++ b/Documentation/usb/power-management.txt
@@ -2,7 +2,7 @@
 
 		 Alan Stern <stern@rowland.harvard.edu>
 
-			    November 10, 2009
+			    December 11, 2009
 
 
 
@@ -29,9 +29,9 @@ 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.  System PM support is present
-only if the kernel was built with CONFIG_SUSPEND or CONFIG_HIBERNATION
-enabled.
+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?
@@ -326,64 +326,63 @@ driver does so by calling these six functions:
 	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 counter in the usb_interface
-structure.  When intf->pm_usage_count is > 0 then the interface is
-deemed to be busy, and the kernel will not autosuspend the interface's
-device.  When intf->pm_usage_count is <= 0 then the interface is
-considered to be idle, and the kernel may autosuspend the device.
+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.
 
-(There is a similar pm_usage_count field in struct usb_device,
+(There is a similar usage counter field in struct usb_device,
 associated with the device itself rather than any of its interfaces.
-This field is used only by the USB core.)
-
-Drivers must not modify intf->pm_usage_count directly; its value
-should be changed only be using the functions listed above.  Drivers
-are responsible for insuring that the overall change to pm_usage_count
-during their lifetime balances out to 0 (it may be necessary for the
-disconnect method to call usb_autopm_put_interface() one or more times
-to fulfill this requirement).  The first two routines use the PM mutex
-in struct usb_device for mutual exclusion; drivers using the async
-routines are responsible for their own synchronization and mutual
-exclusion.
-
-	usb_autopm_get_interface() increments pm_usage_count and
-	attempts an autoresume if the new value is > 0 and the
-	device is suspended.
-
-	usb_autopm_put_interface() decrements pm_usage_count and
-	attempts an autosuspend if the new value is <= 0 and the
-	device isn't suspended.
+This counter is used only by the USB core.)
+
+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 diconnect() 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 differences are: they do
-	not acquire the PM mutex, and they use a workqueue to do their
+	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 not generally not yet be in the desired state.
+	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 pm_usage_count value; they do not attempt to
-	carry out an autoresume or an autosuspend.  Hence they can be
-	called in an atomic context.
+	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 conventional usage pattern is that a driver calls
+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.
+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/level 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 delayed workqueue
-routine is automatically set up to carry out the operation when the
-autosuspend idle-delay has expired.
+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 delay for an autoresume.
+autosuspend, there's no idle-delay for an autoresume.
 
 
 	Other parts of the driver interface
@@ -413,26 +412,27 @@ 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.)
 
-The synchronous usb_autopm_* routines have to run in a sleepable
-process context; they must not be called from an interrupt handler or
-while holding a spinlock.  In fact, the entire autosuspend mechanism
-is not well geared toward interrupt-driven operation.  However there
-is one thing a driver can do in an interrupt handler:
+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);
 
-This sets udev->last_busy to the current time.  udev->last_busy is the
-field used for idle-delay calculations; updating it will cause any
-pending autosuspend to be moved back.  The usb_autopm_* routines will
-also set the last_busy field to the current time.
-
-Calling urb_mark_last_busy() from within an URB completion handler is
-subject to races: The kernel may have just finished deciding the
-device has been idle for long enough but not yet gotten around to
-calling the driver's suspend method.  The driver would have to be
-responsible for synchronizing its suspend method with its URB
-completion handler and causing the autosuspend to fail with -EBUSY if
-an URB had completed too recently.
+in the event handler.  This sets udev->last_busy to the current time.
+udev->last_busy is the field used for idle-delay calculations;
+updating it will cause any pending autosuspend to be moved back.  Most
+of the usb_autopm_* routines will also set the last_busy field to the
+current time.
+
+Asynchronous operation is always subject to races.  For example, a
+driver may call one of the usb_autopm_*_interface_async() routines 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 output 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 checking
@@ -440,75 +440,23 @@ the PM_EVENT_AUTO bit in the message.event argument to the suspend
 method; this bit will be set for internal PM events (autosuspend) and
 clear for external PM events.
 
-Many of the ingredients in the autosuspend framework are oriented
-towards interfaces: The usb_interface structure contains the
-pm_usage_cnt field, and the usb_autopm_* routines take an interface
-pointer as their argument.  But somewhat confusingly, a few of the
-pieces (i.e., usb_mark_last_busy()) use the usb_device structure
-instead.  Drivers need to keep this straight; they can call
-interface_to_usbdev() to find the device structure for a given
-interface.
 
+	Mutual exclusion
+	----------------
 
-	Locking requirements
-	--------------------
-
-All three suspend/resume methods are always called while holding the
-usb_device's PM mutex.  For external events -- but not necessarily for
-autosuspend or autoresume -- the device semaphore (udev->dev.sem) will
-also be held.  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 internal
-suspend/resume events as well.
+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, it can simply acquire udev->pm_mutex. Note that
-calls to resume may be triggered indirectly. Block IO due to memory
-allocations can make the vm subsystem resume a device. Thus while
-holding this lock you must not allocate memory with GFP_KERNEL or
-GFP_NOFS.
-
-Alternatively, if the critical section might call some of the
-usb_autopm_* routines, the driver can avoid deadlock by doing:
-
-	down(&udev->dev.sem);
-	rc = usb_autopm_get_interface(intf);
-
-and at the end of the critical section:
-
-	if (!rc)
-		usb_autopm_put_interface(intf);
-	up(&udev->dev.sem);
-
-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?)
-
-The rules for locking order are:
-
-	Never acquire any device semaphore while holding any PM mutex.
-
-	Never acquire udev->pm_mutex while holding the PM mutex for
-	a device that isn't a descendant of udev.
-
-In other words, PM mutexes should only be acquired going up the device
-tree, and they should be acquired only after locking all the device
-semaphores you need to hold.  These rules don't matter to drivers very
-much; they usually affect just the USB core.
-
-Still, drivers do need to be careful.  For example, many drivers use a
-private mutex to synchronize their normal I/O activities with their
-disconnect method.  Now if the driver supports autosuspend then it
-must call usb_autopm_put_interface() from somewhere -- maybe from its
-close method.  It should make the call while holding the private mutex,
-since a driver shouldn't call any of the usb_autopm_* functions for an
-interface from which it has been unbound.
-
-But the usb_autpm_* routines always acquire the device's PM mutex, and
-consequently the locking order has to be: private mutex first, PM
-mutex second.  Since the suspend method is always called with the PM
-mutex held, it mustn't try to acquire the private mutex.  It has to
-synchronize with the driver's I/O activities in some other way.
+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
@@ -517,22 +465,11 @@ synchronize with the driver's I/O activities in some other way.
 Dynamic power management and system power management can interact in
 a couple of ways.
 
-Firstly, a device may already be manually suspended or 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.  The 2.6.23 kernel obeys this principle
-for manually suspended devices but not for autosuspended devices; they
-do get resumed when the system wakes up.  (Presumably they will be
-autosuspended again after their idle-delay time expires.)  In later
-kernels this behavior will be fixed.
-
-(There is an exception.  If a device would undergo a reset-resume
-instead of a normal resume, and the device is enabled for remote
-wakeup, then the reset-resume takes place even if the device was
-already suspended when the system suspend began.  The justification is
-that a reset-resume is a kind of remote-wakeup event.  Or to put it
-another way, a device which needs a reset won't be able to generate
-normal remote-wakeup signals, so it ought to be resumed immediately.)
+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.
 
 Secondly, a dynamic power-management event may occur as a system
 suspend is underway.  The window for this is short, since system