Alan Stern <stern@rowland.harvard.edu>
- December 11, 2009
+ October 28, 2010
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, 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.)
+relevant attribute files are: wakeup, control, and
+autosuspend_delay_ms. (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. In 2.6.38 the "autosuspend" file will be deprecated
+and replaced by the "autosuspend_delay_ms" file. The only difference
+is that the newer file expresses the delay in milliseconds whereas the
+older file uses seconds. Confusingly, both files are present in 2.6.37
+but only "autosuspend" works.)
power/wakeup
suspended and autoresume was not allowed. This
setting is no longer supported.)
- power/autosuspend
+ power/autosuspend_delay_ms
This file contains an integer value, which is the
- number of seconds the device should remain idle before
- the kernel will autosuspend it (the idle-delay time).
- The default is 2. 0 means to autosuspend as soon as
- the device becomes idle, and negative values mean
- 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/control do
-essentially the same thing -- they both prevent the device from being
-autosuspended. Yes, this is a redundancy in the API.
+ number of milliseconds the device should remain idle
+ before the kernel will autosuspend it (the idle-delay
+ time). The default is 2000. 0 means to autosuspend
+ as soon as the device becomes idle, and negative
+ values mean never to autosuspend. You can write a
+ number to the file to change the autosuspend
+ idle-delay time.
+
+Writing "-1" to power/autosuspend_delay_ms 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/control
-was added in 2.6.34.)
+was added in 2.6.34, and power/autosuspend_delay_ms was added in
+2.6.37 but did not become functional until 2.6.38.)
Changing the default idle-delay time
------------------------------------
-The default autosuspend idle-delay time is controlled by a module
-parameter in usbcore. You can specify the value when usbcore is
-loaded. For example, to set it to 5 seconds instead of 2 you would
+The default autosuspend idle-delay time (in seconds) is controlled by
+a module parameter in usbcore. You can specify the value when usbcore
+is loaded. For example, to set it to 5 seconds instead of 2 you would
do:
modprobe usbcore autosuspend=5
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.
+driver for a laptop's webcam might do this (in recent kernels they
+do), 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,
-which manages keyboards and mice, among other things. Tests with a
-number of keyboards showed that typing on a suspended keyboard, while
-causing the keyboard to do a remote wakeup all right, would
-nonetheless frequently result in lost keystrokes. Tests with mice
-showed that some of them would issue a remote-wakeup request in
-response to button presses but not to motion, and some in response to
-neither.
+autosuspend there are still problems. For example, the usbhid driver,
+which manages keyboards and mice, has autosuspend support. Tests with
+a number of keyboards show that typing on a suspended keyboard, while
+causing the keyboard to do a remote wakeup all right, will nonetheless
+frequently result in lost keystrokes. Tests with mice show that some
+of them will issue a remote-wakeup request in response to button
+presses but not to motion, and some in response to neither.
The kernel will not prevent you from enabling autosuspend on devices
that can't handle it. It is even possible in theory to damage a
-device by suspending it at the wrong time -- for example, suspending a
-USB hard disk might cause it to spin down without parking the heads.
-(Highly unlikely, but possible.) Take care.
+device by suspending it at the wrong time. (Highly unlikely, but
+possible.) Take care.
The driver interface for Power Management
then the interface is considered to be idle, and the kernel may
autosuspend the device.
-(There is a similar usage counter field in struct usb_device,
-associated with the device itself rather than any of its interfaces.
-This counter is used only by the USB core.)
-
Drivers need not be concerned about balancing changes to the usage
counter; the USB core will undo any remaining "get"s when a driver
is unbound from its interface. As a corollary, drivers must not call
autosuspending a keyboard if the user can't cause the keyboard to do a
remote wakeup by typing on it. If the driver sets
intf->needs_remote_wakeup to 1, the kernel won't autosuspend the
-device if remote wakeup isn't available or has been disabled through
-the power/wakeup attribute. (If the device is already autosuspended,
-though, setting this flag won't cause the kernel to autoresume it.
-Normally a driver would set this flag in its probe method, at which
-time the device is guaranteed not to be autosuspended.)
+device if remote wakeup isn't available. (If the device is already
+autosuspended, though, setting this flag won't cause the kernel to
+autoresume it. Normally a driver would set this flag in its probe
+method, at which time the device is guaranteed not to be
+autosuspended.)
If a driver does its I/O asynchronously in interrupt context, it
should call usb_autopm_get_interface_async() before starting output and
usb_mark_last_busy(struct usb_device *udev);
-in the event handler. This sets udev->last_busy to the current time.
-udev->last_busy is the field used for idle-delay calculations;
-updating it will cause any pending autosuspend to be moved back. Most
-of the usb_autopm_* routines will also set the last_busy field to the
-current time.
+in the event handler. This tells the PM core that the device was just
+busy and therefore the next autosuspend idle-delay expiration should
+be pushed back. Many of the usb_autopm_* routines also make this call,
+so drivers need to worry only when interrupt-driven input arrives.
Asynchronous operation is always subject to races. For example, a
-driver may call one of the usb_autopm_*_interface_async() routines at
-a time when the core has just finished deciding the device has been
-idle for long enough but not yet gotten around to calling the driver's
-suspend method. The suspend method must be responsible for
-synchronizing with the output request routine and the URB completion
-handler; it should cause autosuspends to fail with -EBUSY if the
-driver needs to use the device.
+driver may call the usb_autopm_get_interface_async() routine at a time
+when the core has just finished deciding the device has been idle for
+long enough but not yet gotten around to calling the driver's suspend
+method. The suspend method must be responsible for synchronizing with
+the I/O request routine and the URB completion handler; it should
+cause autosuspends to fail with -EBUSY if the driver needs to use the
+device.
External suspend calls should never be allowed to fail in this way,
only autosuspend calls. The driver can tell them apart by checking
occurs. Since system suspends are supposed to be as transparent as
possible, the device should remain suspended following the system
resume. But this theory may not work out well in practice; over time
-the kernel's behavior in this regard has changed.
+the kernel's behavior in this regard has changed. As of 2.6.37 the
+policy is to resume all devices during a system resume and let them
+handle their own runtime suspends afterward.
Secondly, a dynamic power-management event may occur as a system
suspend is underway. The window for this is short, since system
int status;
usb_mark_last_busy(udev);
- status = pm_runtime_put_sync(&udev->dev);
- dev_vdbg(&udev->dev, "%s: cnt %d -> %d\n",
- __func__, atomic_read(&udev->dev.power.usage_count),
- status);
-}
-
-/**
- * usb_try_autosuspend_device - attempt an autosuspend of a USB device and its interfaces
- * @udev: the usb_device to autosuspend
- *
- * This routine should be called when a core subsystem thinks @udev may
- * be ready to autosuspend.
- *
- * @udev's usage counter left unchanged. If it is 0 and all the interfaces
- * are inactive then an autosuspend will be attempted. The attempt may
- * fail or be delayed.
- *
- * The caller must hold @udev's device lock.
- *
- * This routine can run only in process context.
- */
-void usb_try_autosuspend_device(struct usb_device *udev)
-{
- int status;
-
- status = pm_runtime_idle(&udev->dev);
+ status = pm_runtime_put_sync_autosuspend(&udev->dev);
dev_vdbg(&udev->dev, "%s: cnt %d -> %d\n",
__func__, atomic_read(&udev->dev.power.usage_count),
status);
void usb_autopm_put_interface_async(struct usb_interface *intf)
{
struct usb_device *udev = interface_to_usbdev(intf);
- unsigned long last_busy;
- int status = 0;
+ int status;
- last_busy = udev->dev.power.last_busy;
usb_mark_last_busy(udev);
atomic_dec(&intf->pm_usage_cnt);
- pm_runtime_put_noidle(&intf->dev);
-
- if (udev->dev.power.runtime_auto) {
- /* Optimization: Don't schedule a delayed autosuspend if
- * the timer is already running and the expiration time
- * wouldn't change.
- *
- * We have to use the interface's timer. Attempts to
- * schedule a suspend for the device would fail because
- * the interface is still active.
- */
- if (intf->dev.power.timer_expires == 0 ||
- round_jiffies_up(last_busy) !=
- round_jiffies_up(jiffies)) {
- status = pm_schedule_suspend(&intf->dev,
- jiffies_to_msecs(
- round_jiffies_up_relative(
- udev->autosuspend_delay)));
- }
- }
+ status = pm_runtime_put(&intf->dev);
dev_vdbg(&intf->dev, "%s: cnt %d -> %d\n",
__func__, atomic_read(&intf->dev.power.usage_count),
status);
{
int w, i;
struct usb_interface *intf;
- unsigned long suspend_time, j;
/* Fail if autosuspend is disabled, or any interfaces are in use, or
* any interface drivers require remote wakeup but it isn't available.
return -EOPNOTSUPP;
}
udev->do_remote_wakeup = w;
-
- /* If everything is okay but the device hasn't been idle for long
- * enough, queue a delayed autosuspend request.
- */
- j = ACCESS_ONCE(jiffies);
- suspend_time = udev->dev.power.last_busy + udev->autosuspend_delay;
- if (time_before(j, suspend_time)) {
- pm_schedule_suspend(&udev->dev, jiffies_to_msecs(
- round_jiffies_up_relative(suspend_time - j)));
- return -EAGAIN;
- }
return 0;
}
status = usb_suspend_both(udev, PMSG_AUTO_SUSPEND);
- /* If an interface fails the suspend, adjust the last_busy
- * time so that we don't get another suspend attempt right
- * away.
- */
- if (status) {
- udev->dev.power.last_busy = jiffies +
- (udev->autosuspend_delay == 0 ? HZ/2 : 0);
- }
-
/* Prevent the parent from suspending immediately after */
- else if (udev->parent)
+ if (status == 0 && udev->parent)
usb_mark_last_busy(udev->parent);
return status;
* autosuspend checks.
*/
if (autosuspend_check(udev) == 0)
- pm_runtime_suspend(dev);
+ pm_runtime_autosuspend(dev);
return 0;
}
git.openpandora.org / pandora-kernel.git / commitdiff