Linux sysfs PCI power control docs
Posted by Anonymous on Thu 5th Aug 2021 11:52
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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 and the special value
                "n/a" means that user space cannot accept any resume latency at
                all for the given 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_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/runtime_status
Date:           April 2010
Contact:        Rafael J. Wysocki <rjw@rjwysocki.net>
Description:
                The /sys/devices/.../power/runtime_status attribute contains
                the current runtime PM status of the device, which may be
                "suspended", "suspending", "resuming", "active", "error" (fatal
                error), or "unsupported" (runtime PM is disabled).