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-rw-r--r--Documentation/usb/power-management.txt19
1 files changed, 11 insertions, 8 deletions
diff --git a/Documentation/usb/power-management.txt b/Documentation/usb/power-management.txt
index 2790ad48cfc2..b29d8e56cf28 100644
--- a/Documentation/usb/power-management.txt
+++ b/Documentation/usb/power-management.txt
@@ -107,7 +107,9 @@ allowed to issue dynamic suspends.
107The user interface for controlling dynamic PM is located in the power/ 107The user interface for controlling dynamic PM is located in the power/
108subdirectory of each USB device's sysfs directory, that is, in 108subdirectory of each USB device's sysfs directory, that is, in
109/sys/bus/usb/devices/.../power/ where "..." is the device's ID. The 109/sys/bus/usb/devices/.../power/ where "..." is the device's ID. The
110relevant attribute files are: wakeup, level, and autosuspend. 110relevant attribute files are: wakeup, control, and autosuspend.
111(There may also be a file named "level"; this file was deprecated
112as of the 2.6.35 kernel and replaced by the "control" file.)
111 113
112 power/wakeup 114 power/wakeup
113 115
@@ -120,7 +122,7 @@ relevant attribute files are: wakeup, level, and autosuspend.
120 while the device is suspended, the change won't take 122 while the device is suspended, the change won't take
121 effect until the following suspend.) 123 effect until the following suspend.)
122 124
123 power/level 125 power/control
124 126
125 This file contains one of two words: "on" or "auto". 127 This file contains one of two words: "on" or "auto".
126 You can write those words to the file to change the 128 You can write those words to the file to change the
@@ -148,14 +150,15 @@ relevant attribute files are: wakeup, level, and autosuspend.
148 never to autosuspend. You can write a number to the 150 never to autosuspend. You can write a number to the
149 file to change the autosuspend idle-delay time. 151 file to change the autosuspend idle-delay time.
150 152
151Writing "-1" to power/autosuspend and writing "on" to power/level do 153Writing "-1" to power/autosuspend and writing "on" to power/control do
152essentially the same thing -- they both prevent the device from being 154essentially the same thing -- they both prevent the device from being
153autosuspended. Yes, this is a redundancy in the API. 155autosuspended. Yes, this is a redundancy in the API.
154 156
155(In 2.6.21 writing "0" to power/autosuspend would prevent the device 157(In 2.6.21 writing "0" to power/autosuspend would prevent the device
156from being autosuspended; the behavior was changed in 2.6.22. The 158from being autosuspended; the behavior was changed in 2.6.22. The
157power/autosuspend attribute did not exist prior to 2.6.21, and the 159power/autosuspend attribute did not exist prior to 2.6.21, and the
158power/level attribute did not exist prior to 2.6.22.) 160power/level attribute did not exist prior to 2.6.22. power/control
161was added in 2.6.34.)
159 162
160 163
161 Changing the default idle-delay time 164 Changing the default idle-delay time
@@ -212,7 +215,7 @@ among printers and scanners, but plenty of other types of device have
212the same deficiency. 215the same deficiency.
213 216
214For this reason, by default the kernel disables autosuspend (the 217For this reason, by default the kernel disables autosuspend (the
215power/level attribute is initialized to "on") for all devices other 218power/control attribute is initialized to "on") for all devices other
216than hubs. Hubs, at least, appear to be reasonably well-behaved in 219than hubs. Hubs, at least, appear to be reasonably well-behaved in
217this regard. 220this regard.
218 221
@@ -373,7 +376,7 @@ usb_autopm_put_interface() in its close or release routine. But other
373patterns are possible. 376patterns are possible.
374 377
375The autosuspend attempts mentioned above will often fail for one 378The autosuspend attempts mentioned above will often fail for one
376reason or another. For example, the power/level attribute might be 379reason or another. For example, the power/control attribute might be
377set to "on", or another interface in the same device might not be 380set to "on", or another interface in the same device might not be
378idle. This is perfectly normal. If the reason for failure was that 381idle. This is perfectly normal. If the reason for failure was that
379the device hasn't been idle for long enough, a timer is scheduled to 382the device hasn't been idle for long enough, a timer is scheduled to
@@ -394,12 +397,12 @@ Drivers can enable autosuspend for their devices by calling
394 397
395in their probe() routine, if they know that the device is capable of 398in their probe() routine, if they know that the device is capable of
396suspending and resuming correctly. This is exactly equivalent to 399suspending and resuming correctly. This is exactly equivalent to
397writing "auto" to the device's power/level attribute. Likewise, 400writing "auto" to the device's power/control attribute. Likewise,
398drivers can disable autosuspend by calling 401drivers can disable autosuspend by calling
399 402
400 usb_disable_autosuspend(struct usb_device *udev); 403 usb_disable_autosuspend(struct usb_device *udev);
401 404
402This is exactly the same as writing "on" to the power/level attribute. 405This is exactly the same as writing "on" to the power/control attribute.
403 406
404Sometimes a driver needs to make sure that remote wakeup is enabled 407Sometimes a driver needs to make sure that remote wakeup is enabled
405during autosuspend. For example, there's not much point 408during autosuspend. For example, there's not much point