lk/linux-kernel-test
1
0
Fork 0
Code Issues Pull Requests Releases Wiki Activity

USB: use the runtime-PM autosuspend implementation

Browse Source 
This patch (as1428) converts USB over to the new runtime-PM core
autosuspend framework.  One slightly awkward aspect of the conversion
is that USB devices will now have two suspend-delay attributes: the
old power/autosuspend file and the new power/autosuspend_delay_ms
file.  One expresses the delay time in seconds and the other in
milliseconds, but otherwise they do the same thing.  The old attribute
can be deprecated and then removed eventually.

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
2010-11-15 15:57:51 -05:00
committed by Greg Kroah-Hartman
parent 6ddf27cdbc
commit fcc4a01eb8
8 changed files with 70 additions and 166 deletions
Download Patch File Download Diff File Expand all files Collapse all files

111
Documentation/usb/power-management.txt
View File

@@ -2,7 +2,7 @@
Alan Stern <stern@rowland.harvard.edu>
December 11, 2009
October 28, 2010
@@ -107,9 +107,14 @@ 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, 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
@@ -140,33 +145,36 @@ as of the 2.6.35 kernel and replaced by the "control" file.)
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.
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 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.
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
@@ -234,25 +242,23 @@ every device.
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
@@ -336,10 +342,6 @@ autosuspend the interface's device. When the usage counter is = 0
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
@@ -409,11 +411,11 @@ during autosuspend. For example, there's not much point
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
@@ -422,20 +424,19 @@ it receives an input event, it should call
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
@@ -472,7 +473,9 @@ Firstly, a device may already be autosuspended when a system suspend
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