forge/linux-pinenote
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

USB: power management documentation update

Browse source 
This patch (as1313) updates the documentation concerning USB power
management.

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 2009-12-08 15:49:48 -05:00 • committed by Greg Kroah-Hartman
parent f42ecb2808
commit baf67741bf
2 changed files with 25 additions and 34 deletions
Download patch file Download diff file Expand all files Collapse all files

18
Documentation/ABI/testing/sysfs-bus-usb
View file

@ -21,25 +21,27 @@ Contact: Alan Stern <stern@rowland.harvard.edu>
Description:
Each USB device directory will contain a file named
power/level. This file holds a power-level setting for
the device, one of "on", "auto", or "suspend".
the device, either "on" or "auto".
"on" means that the device is not allowed to autosuspend,
although normal suspends for system sleep will still
be honored. "auto" means the device will autosuspend
and autoresume in the usual manner, according to the
capabilities of its driver. "suspend" means the device
is forced into a suspended state and it will not autoresume
in response to I/O requests. However remote-wakeup requests
from the device may still be enabled (the remote-wakeup
setting is controlled separately by the power/wakeup
attribute).
capabilities of its driver.
During normal use, devices should be left in the "auto"
level. The other levels are meant for administrative uses.
level. The "on" level is meant for administrative uses.
If you want to suspend a device immediately but leave it
free to wake up in response to I/O requests, you should
write "0" to power/autosuspend.
Device not capable of proper suspend and resume should be
left in the "on" level. Although the USB spec requires
devices to support suspend/resume, many of them do not.
In fact so many don't that by default, the USB core
initializes all non-hub devices in the "on" level. Some
drivers may change this setting when they are bound.
What: /sys/bus/usb/devices/.../power/persist
Date: May 2007
KernelVersion: 2.6.23