path: root/Documentation/ABI/testing/sysfs-bus-usb
diff options
Diffstat (limited to 'Documentation/ABI/testing/sysfs-bus-usb')
1 files changed, 10 insertions, 8 deletions
diff --git a/Documentation/ABI/testing/sysfs-bus-usb b/Documentation/ABI/testing/sysfs-bus-usb
index deb6b489e4e..a07c0f366f9 100644
--- a/Documentation/ABI/testing/sysfs-bus-usb
+++ b/Documentation/ABI/testing/sysfs-bus-usb
@@ -21,25 +21,27 @@ Contact: Alan Stern <stern@rowland.harvard.edu>
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