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-rw-r--r--Documentation/usb/power-management.txt22
1 files changed, 17 insertions, 5 deletions
diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index e48ea1d5101..ad642615ad4 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