USB: implement usb_enable_autosuspend

This patch (as1326) adds usb_enable_autosuspend() and
usb_disable_autosuspend() routines for use by drivers.  If a driver
knows that its device can handle suspends and resumes correctly, it
can enable autosuspend all by itself.  This is equivalent to the user
writing "auto" to the device's power/level attribute.

The implementation differs slightly from what it used to be.  Now
autosuspend is disabled simply by doing usb_autoresume_device() (to
increment the usage counter) and enabled by doing
usb_autosuspend_device() (to decrement the usage counter).

The set_level() attribute method is updated to use the new routines,
and the USB Power-Management documentation is updated.

The patch adds a usb_enable_autosuspend() call to the hub driver's
probe routine, allowing the special-case code for hubs in quirks.c to
be removed.

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

1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index 3bf6818c8cf5..e3fa189c257a 100644
--- a/Documentation/usb/power-management.txt
+++ b/Documentation/usb/power-management.txt
@@ -229,6 +229,11 @@ 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, 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, there are
 experimental patches adding autosuspend support to the usbhid driver,
@@ -384,6 +389,19 @@ autosuspend, there's no 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/level 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/level 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