path: root/Documentation/usb
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authorAlan Stern <stern@rowland.harvard.edu>2010-01-08 12:56:54 -0500
committerGreg Kroah-Hartman <gregkh@suse.de>2010-03-02 14:54:10 -0800
commit088f7fec8a0e683db72fd8826c5d3ab914e197b1 (patch)
tree971ef100d0db9727e4403865b67c72de62e8247a /Documentation/usb
parent0c4db6df915bc470f0cd32fe48287fa6eb6adfb4 (diff)
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>
Diffstat (limited to 'Documentation/usb')
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