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linux/Documentation/ABI/testing/sysfs-devices-power
Geert Uytterhoeven d054980165 PM / wakeup: Correct presence vs. emptiness of wakeup_* attributes 
According to the documentation, the various wakeup_* attributes in sysfs
are not present if the device is not enabled to wake up the system.

This is not correct: the attributes are not present if the device is not
capable to wake up the system. They are empty if the device is not enabled
to wake up the system.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-04-07 14:18:24 +02:00

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What: /sys/devices/.../power/
Date: January 2009
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../power directory contains attributes
allowing the user space to check and modify some power
management related properties of given device.
What: /sys/devices/.../power/wakeup
Date: January 2009
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../power/wakeup attribute allows the user
space to check if the device is enabled to wake up the system
from sleep states, such as the memory sleep state (suspend to
RAM) and hibernation (suspend to disk), and to enable or disable
it to do that as desired.
Some devices support "wakeup" events, which are hardware signals
used to activate the system from a sleep state. Such devices
have one of the following two values for the sysfs power/wakeup
file:
+ "enabled\n" to issue the events;
+ "disabled\n" not to do so;
In that cases the user space can change the setting represented
by the contents of this file by writing either "enabled", or
"disabled" to it.
For the devices that are not capable of generating system wakeup
events this file is not present. In that case the device cannot
be enabled to wake up the system from sleep states.
What: /sys/devices/.../power/control
Date: January 2009
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../power/control attribute allows the user
space to control the run-time power management of the device.
All devices have one of the following two values for the
power/control file:
+ "auto\n" to allow the device to be power managed at run time;
+ "on\n" to prevent the device from being power managed;
The default for all devices is "auto", which means that they may
be subject to automatic power management, depending on their
drivers. Changing this attribute to "on" prevents the driver
from power managing the device at run time. Doing that while
the device is suspended causes it to be woken up.
What: /sys/devices/.../power/async
Date: January 2009
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../async attribute allows the user space to
enable or diasble the device's suspend and resume callbacks to
be executed asynchronously (ie. in separate threads, in parallel
with the main suspend/resume thread) during system-wide power
transitions (eg. suspend to RAM, hibernation).
All devices have one of the following two values for the
power/async file:
+ "enabled\n" to permit the asynchronous suspend/resume;
+ "disabled\n" to forbid it;
The value of this attribute may be changed by writing either
"enabled", or "disabled" to it.
It generally is unsafe to permit the asynchronous suspend/resume
of a device unless it is certain that all of the PM dependencies
of the device are known to the PM core. However, for some
devices this attribute is set to "enabled" by bus type code or
device drivers and in that cases it should be safe to leave the
default value.
What: /sys/devices/.../power/wakeup_count
Date: September 2010
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_count attribute contains the number
of signaled wakeup events associated with the device. This
attribute is read-only. If the device is not capable to wake up
the system from sleep states, this attribute is not present.
If the device is not enabled to wake up the system from sleep
states, this attribute is empty.
What: /sys/devices/.../power/wakeup_active_count
Date: September 2010
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_active_count attribute contains the
number of times the processing of wakeup events associated with
the device was completed (at the kernel level). This attribute
is read-only. If the device is not capable to wake up the
system from sleep states, this attribute is not present. If
the device is not enabled to wake up the system from sleep
states, this attribute is empty.
What: /sys/devices/.../power/wakeup_abort_count
Date: February 2012
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_abort_count attribute contains the
number of times the processing of a wakeup event associated with
the device might have aborted system transition into a sleep
state in progress. This attribute is read-only. If the device
is not capable to wake up the system from sleep states, this
attribute is not present. If the device is not enabled to wake
up the system from sleep states, this attribute is empty.
What: /sys/devices/.../power/wakeup_expire_count
Date: February 2012
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_expire_count attribute contains the
number of times a wakeup event associated with the device has
been reported with a timeout that expired. This attribute is
read-only. If the device is not capable to wake up the system
from sleep states, this attribute is not present. If the
device is not enabled to wake up the system from sleep states,
this attribute is empty.
What: /sys/devices/.../power/wakeup_active
Date: September 2010
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_active attribute contains either 1,
or 0, depending on whether or not a wakeup event associated with
the device is being processed (1). This attribute is read-only.
If the device is not capable to wake up the system from sleep
states, this attribute is not present. If the device is not
enabled to wake up the system from sleep states, this attribute
is empty.
What: /sys/devices/.../power/wakeup_total_time_ms
Date: September 2010
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_total_time_ms attribute contains
the total time of processing wakeup events associated with the
device, in milliseconds. This attribute is read-only. If the
device is not capable to wake up the system from sleep states,
this attribute is not present. If the device is not enabled to
wake up the system from sleep states, this attribute is empty.
What: /sys/devices/.../power/wakeup_max_time_ms
Date: September 2010
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_max_time_ms attribute contains
the maximum time of processing a single wakeup event associated
with the device, in milliseconds. This attribute is read-only.
If the device is not capable to wake up the system from sleep
states, this attribute is not present. If the device is not
enabled to wake up the system from sleep states, this attribute
is empty.
What: /sys/devices/.../power/wakeup_last_time_ms
Date: September 2010
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_last_time_ms attribute contains
the value of the monotonic clock corresponding to the time of
signaling the last wakeup event associated with the device, in
milliseconds. This attribute is read-only. If the device is
not enabled to wake up the system from sleep states, this
attribute is not present. If the device is not enabled to wake
up the system from sleep states, this attribute is empty.
What: /sys/devices/.../power/wakeup_prevent_sleep_time_ms
Date: February 2012
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../wakeup_prevent_sleep_time_ms attribute
contains the total time the device has been preventing
opportunistic transitions to sleep states from occurring.
This attribute is read-only. If the device is not capable to
wake up the system from sleep states, this attribute is not
present. If the device is not enabled to wake up the system
from sleep states, this attribute is empty.
What: /sys/devices/.../power/autosuspend_delay_ms
Date: September 2010
Contact: Alan Stern <stern@rowland.harvard.edu>
Description:
The /sys/devices/.../power/autosuspend_delay_ms attribute
contains the autosuspend delay value (in milliseconds). Some
drivers do not want their device to suspend as soon as it
becomes idle at run time; they want the device to remain
inactive for a certain minimum period of time first. That
period is called the autosuspend delay. Negative values will
prevent the device from being suspended at run time (similar
to writing "on" to the power/control attribute). Values >=
1000 will cause the autosuspend timer expiration to be rounded
up to the nearest second.
Not all drivers support this attribute. If it isn't supported,
attempts to read or write it will yield I/O errors.
What: /sys/devices/.../power/pm_qos_resume_latency_us
Date: March 2012
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../power/pm_qos_resume_latency_us attribute
contains the PM QoS resume latency limit for the given device,
which is the maximum allowed time it can take to resume the
device, after it has been suspended at run time, from a resume
request to the moment the device will be ready to process I/O,
in microseconds. If it is equal to 0, however, this means that
the PM QoS resume latency may be arbitrary.
Not all drivers support this attribute. If it isn't supported,
it is not present.
This attribute has no effect on system-wide suspend/resume and
hibernation.
What: /sys/devices/.../power/pm_qos_latency_tolerance_us
Date: January 2014
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../power/pm_qos_latency_tolerance_us attribute
contains the PM QoS active state latency tolerance limit for the
given device in microseconds. That is the maximum memory access
latency the device can suffer without any visible adverse
effects on user space functionality. If that value is the
string "any", the latency does not matter to user space at all,
but hardware should not be allowed to set the latency tolerance
for the device automatically.
Reading "auto" from this file means that the maximum memory
access latency for the device may be determined automatically
by the hardware as needed. Writing "auto" to it allows the
hardware to be switched to this mode if there are no other
latency tolerance requirements from the kernel side.
This attribute is only present if the feature controlled by it
is supported by the hardware.
This attribute has no effect on runtime suspend and resume of
devices and on system-wide suspend/resume and hibernation.
What: /sys/devices/.../power/pm_qos_no_power_off
Date: September 2012
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../power/pm_qos_no_power_off attribute
is used for manipulating the PM QoS "no power off" flag. If
set, this flag indicates to the kernel that power should not
be removed entirely from the device.
Not all drivers support this attribute. If it isn't supported,
it is not present.
This attribute has no effect on system-wide suspend/resume and
hibernation.
What: /sys/devices/.../power/pm_qos_remote_wakeup
Date: September 2012
Contact: Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
The /sys/devices/.../power/pm_qos_remote_wakeup attribute
is used for manipulating the PM QoS "remote wakeup required"
flag. If set, this flag indicates to the kernel that the
device is a source of user events that have to be signaled from
its low-power states.
Not all drivers support this attribute. If it isn't supported,
it is not present.
This attribute has no effect on system-wide suspend/resume and
hibernation.
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