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USB: deprecate the power/level sysfs attribute 

This patch (as1367) deprecates USB's power/level sysfs attribute in
favor of the power/control attribute provided by the runtime PM core.
The two attributes do the same thing.

It would be nice to replace power/level with a symlink to
power/control, but at the moment sysfs doesn't offer any way to do so.

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 2010-04-02 13:22:16 -04:00 committed by Greg Kroah-Hartman
parent 9e18c82165
commit a90309860b
4 changed files with 54 additions and 36 deletions
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31
Documentation/ABI/obsolete/sysfs-bus-usb Normal file
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@ -0,0 +1,31 @@
What: /sys/bus/usb/devices/.../power/level
Date: March 2007
KernelVersion: 2.6.21
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, 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.
During normal use, devices should be left in the "auto"
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.
This file is deprecated and will be removed after 2010.
Use the power/control file instead; it does exactly the
same thing.

28
Documentation/ABI/testing/sysfs-bus-usb
View File

@ -14,34 +14,6 @@ Description:
The autosuspend delay for newly-created devices is set to
the value of the usbcore.autosuspend module parameter.
What: /sys/bus/usb/devices/.../power/level
Date: March 2007
KernelVersion: 2.6.21
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, 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.
During normal use, devices should be left in the "auto"
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

19
Documentation/usb/power-management.txt
View File

@ -107,7 +107,9 @@ allowed to issue dynamic suspends.
The user interface for controlling dynamic PM is located in the power/
subdirectory of each USB device's sysfs directory, that is, in
/sys/bus/usb/devices/.../power/ where "..." is the device's ID. The
relevant attribute files are: wakeup, level, and autosuspend.
relevant attribute files are: wakeup, control, and autosuspend.
(There may also be a file named "level"; this file was deprecated
as of the 2.6.35 kernel and replaced by the "control" file.)
power/wakeup
@ -120,7 +122,7 @@ relevant attribute files are: wakeup, level, and autosuspend.
while the device is suspended, the change won't take
effect until the following suspend.)
power/level
power/control
This file contains one of two words: "on" or "auto".
You can write those words to the file to change the
@ -148,14 +150,15 @@ relevant attribute files are: wakeup, level, and autosuspend.
never to autosuspend. You can write a number to the
file to change the autosuspend idle-delay time.
Writing "-1" to power/autosuspend and writing "on" to power/level do
Writing "-1" to power/autosuspend and writing "on" to power/control do
essentially the same thing -- they both prevent the device from being
autosuspended. Yes, this is a redundancy in the API.
(In 2.6.21 writing "0" to power/autosuspend would prevent the device
from being autosuspended; the behavior was changed in 2.6.22. The
power/autosuspend attribute did not exist prior to 2.6.21, and the
power/level attribute did not exist prior to 2.6.22.)
power/level attribute did not exist prior to 2.6.22. power/control
was added in 2.6.34.)
Changing the default idle-delay time
@ -212,7 +215,7 @@ among printers and scanners, but plenty of other types of device have
the same deficiency.
For this reason, by default the kernel disables autosuspend (the
power/level attribute is initialized to "on") for all devices other
power/control attribute is initialized to "on") for all devices other
than hubs. Hubs, at least, appear to be reasonably well-behaved in
this regard.
@ -373,7 +376,7 @@ usb_autopm_put_interface() in its close or release routine. But other
patterns are possible.
The autosuspend attempts mentioned above will often fail for one
reason or another. For example, the power/level attribute might be
reason or another. For example, the power/control attribute might be
set to "on", or another interface in the same device might not be
idle. This is perfectly normal. If the reason for failure was that
the 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
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,
writing "auto" to the device's power/control 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.
This is exactly the same as writing "on" to the power/control attribute.
Sometimes a driver needs to make sure that remote wakeup is enabled
during autosuspend. For example, there's not much point

12
drivers/usb/core/sysfs.c
View File

@ -383,12 +383,23 @@ static DEVICE_ATTR(autosuspend, S_IRUGO | S_IWUSR,
static const char on_string[] = "on";
static const char auto_string[] = "auto";
static void warn_level(void) {
static int level_warned;
if (!level_warned) {
level_warned = 1;
printk(KERN_WARNING "WARNING! power/level is deprecated; "
"use power/control instead\n");
}
}
static ssize_t
show_level(struct device *dev, struct device_attribute *attr, char *buf)
{
struct usb_device *udev = to_usb_device(dev);
const char *p = auto_string;
warn_level();
if (udev->state != USB_STATE_SUSPENDED && !udev->dev.power.runtime_auto)
p = on_string;
return sprintf(buf, "%s\n", p);
@ -403,6 +414,7 @@ set_level(struct device *dev, struct device_attribute *attr,
char *cp;
int rc = count;
warn_level();
cp = memchr(buf, '\n', count);
if (cp)
len = cp - buf;