USB: add asynchronous autosuspend/autoresume support

This patch (as1160b) adds support routines for asynchronous autosuspend
and autoresume, with accompanying documentation updates.  There
already are several potential users of this interface, and others are
likely to arise as autosuspend support becomes more widespread.

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

1 files changed, 17 insertions, 5 deletions

diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index e48ea1d51010..ad642615ad4c 100644
--- a/Documentation/usb/power-management.txt
+++ b/Documentation/usb/power-management.txt
@@ -313,11 +313,13 @@ 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 three functions:
+driver does so by calling these five functions:
 
         int  usb_autopm_get_interface(struct usb_interface *intf);
         void usb_autopm_put_interface(struct usb_interface *intf);
         int  usb_autopm_set_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);
 
 The functions work by maintaining a counter in the usb_interface
 structure.  When intf->pm_usage_count is > 0 then the interface is
@@ -330,10 +332,12 @@ associated with the device itself rather than any of its interfaces.
 This field is used only by the USB core.)
 
 The driver owns intf->pm_usage_count; it can modify the value however
-and whenever it likes.  A nice aspect of the usb_autopm_* routines is
-that the changes they make are protected by the usb_device structure's
-PM mutex (udev->pm_mutex); however drivers may change pm_usage_count
-without holding the mutex.
+and whenever it likes.  A nice aspect of the non-async usb_autopm_*
+routines is that the changes they make are protected by the usb_device
+structure's PM mutex (udev->pm_mutex); however drivers may change
+pm_usage_count without holding the mutex.  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
@@ -348,6 +352,14 @@ without holding the mutex.
         is suspended, and it attempts an autosuspend if the value is
         <= 0 and the device isn't suspended.
 
+        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
+        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.
+
 There also are a couple of utility routines drivers can use:
 
         usb_autopm_enable() sets pm_usage_cnt to 0 and then calls