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USB: add asynchronous autosuspend/autoresume support

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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>
This commit is contained in:
Alan Stern 2008-11-12 16:19:49 -05:00 • committed by Greg Kroah-Hartman
parent d4f373e57d
commit 9ac39f28b5
6 changed files with 117 additions and 7 deletions
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22
Documentation/usb/power-management.txt
View file

@ -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