Lines Matching +full:auto +full:- +full:pm
1 .. _usb-power-management:
7 :Date: Last-updated: February 2014
11 ---------
15 * Forms of dynamic PM
16 * The user interface for dynamic PM
17 * Changing the default idle-delay time
23 * Interaction between dynamic PM and system PM
24 * xHCI hardware link PM
31 -------------------------
33 Power Management (PM) is the practice of saving energy by suspending
35 component is ``suspended`` it is in a nonfunctional low-power state; it
37 ``resumed`` (returned to a functional full-power state) when the kernel
38 needs to use it. (There also are forms of PM in which components are
48 dynamic PM is implemented in the USB subsystem, although system PM is
50 information about system PM).
52 System PM support is present only if the kernel was built with
53 ``CONFIG_SUSPEND`` or ``CONFIG_HIBERNATION`` enabled. Dynamic PM support
58 [Historically, dynamic PM support for USB was present only if the
60 ``CONFIG_PM_RUNTIME``). Starting with the 3.10 kernel release, dynamic PM
67 ----------------------
85 --------------------------
100 Forms of dynamic PM
101 -------------------
106 of time, the so-called idle-delay time.
118 usblp, usblcd, and usb-skeleton (which doesn't count). If a
119 non-supporting driver is bound to a device, the device won't be
133 The user interface for dynamic PM
134 ---------------------------------
136 The user interface for controlling dynamic PM is located in the ``power/``
161 This file contains one of two words: ``on`` or ``auto``.
165 - ``on`` means that the device should be resumed and
169 - ``auto`` is the normal state in which the kernel is
181 before the kernel will autosuspend it (the idle-delay
186 idle-delay time.
188 Writing ``-1`` to ``power/autosuspend_delay_ms`` and writing ``on`` to
189 ``power/control`` do essentially the same thing -- they both prevent the
201 Changing the default idle-delay time
202 ------------------------------------
204 The default autosuspend idle-delay time (in seconds) is controlled by
233 then each new USB device will have its autosuspend idle-delay
234 initialized to 5. (The idle-delay values for already existing devices
237 Setting the initial default idle-delay to -1 will prevent any
243 --------
255 than hubs. Hubs, at least, appear to be reasonably well-behaved in
262 This means that non-hub devices won't be autosuspended unless the user
268 also change the idle-delay time; 2 seconds is not the best choice for
283 of them will issue a remote-wakeup request in response to button
293 -----------------------------------------
305 - The ``suspend`` method is called to warn the driver that the
311 - The ``resume`` method is called to tell the driver that the
315 - The ``reset_resume`` method is called to tell the driver that
327 possible to work around the hibernation-forces-disconnect problem by
331 :ref:`usb-persist`) and it can also be used under certain
350 ---------------------------------------------------
379 has returned -- say from within a work-queue routine -- provided they
395 their non-async counterparts. The big difference is that they
417 carry out the operation automatically when the autosuspend idle-delay
422 autosuspend, there's no idle-delay for an autoresume.
426 -----------------------------------
434 writing ``auto`` to the device's ``power/control`` attribute. Likewise,
445 ``intf->needs_remote_wakeup`` to 1, the kernel won't autosuspend the
459 in the event handler. This tells the PM core that the device was just
460 busy and therefore the next autosuspend idle-delay expiration should
462 so drivers need to worry only when interrupt-driven input arrives.
470 cause autosuspends to fail with -EBUSY if the driver needs to use the
476 method; it will return True for internal PM events (autosuspend) and
477 False for external PM events.
481 ----------------
483 For external events -- but not necessarily for autosuspend or
484 autoresume -- the device semaphore (udev->dev.sem) will be held when a
494 external PM calls, and the :c:func:`usb_autopm_get_interface` will prevent any
495 internal PM calls, even if it fails. (Exercise: Why?)
498 Interaction between dynamic PM and system PM
499 --------------------------------------------
512 Secondly, a dynamic power-management event may occur as a system
515 For example, a suspended device may send a remote-wakeup signal while
524 xHCI hardware link PM
525 ---------------------
528 (xHCI 1.0 feature) and usb3.0 devices which support link PM. By
552 When a USB 3.0 lpm-capable device is plugged in to a
553 xHCI host which supports link PM, it will check if U1
563 ----------------------
569 In the case of a root or platform-internal hub the host controller
597 http://dl.dropbox.com/u/96820575/sarah-sharp-lpt-port-power-off2-mini.pdf
601 http://linuxplumbers.ubicast.tv/videos/usb-port-power-off-kerneluserspace-api/
613 -------------------------------------
615 The port power control mechanism uses the PM runtime system. Poweroff is
618 ``ClearPortFeature(PORT_POWER)`` request. Otherwise, it will honor the pm
631 lost and all attached child-devices will disconnect. A good rule of thumb is
639 prefix=/sys/devices/pci0000:00/0000:00:14.0/usb3/3-1
645 $prefix/3-1:1.0/3-1-port1/device
647 $prefix/3-1:1.0/3-1-port1/power/pm_qos_no_power_off
648 $prefix/3-1:1.0/3-1-port1/device/power/control
649 $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intf0>/driver/unbind
650 $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intf1>/driver/unbind
652 $prefix/3-1:1.0/3-1-port1/device/3-1.1:<intfN>/driver/unbind
656 hi-speed peer::
658 $prefix/3-1:1.0/3-1-port1/peer -> ../../../../usb2/2-1/2-1:1.0/2-1-port1
659 ../../../../usb2/2-1/2-1:1.0/2-1-port1/peer -> ../../../../usb3/3-1/3-1:1.0/3-1-port1
662 peer ports are simply the hi-speed and superspeed interface pins that
667 connection and attempt to connect to the hi-speed pins. The
670 1. Port suspend is sequenced to guarantee that hi-speed ports are powered-off
671 before their superspeed peer is permitted to power-off. The implication is
673 not cause the port to power-off until its highspeed peer has gone to its
675 if it wants to guarantee that a superspeed port will power-off.
677 2. Port resume is sequenced to force a superspeed port to power-on prior to its
684 child device can suspend (autosuspend-delay) and resume (reset-resume
689 ``<hubdev-portX>/power/pm_qos_no_power_off``:
697 ``<hubdev-portX>/power/runtime_status``:
702 ``<hubdev-portX>/connect_type``:
703 An advisory read-only flag to userspace indicating the
729 powered-off at all times.
738 - since we are relying on the BIOS to get this ACPI
742 - Take care in clearing ``pm_qos_no_power_off``. Once
750 Must be ``auto``, and the port will not
758 power session loss (suspend / port-power event). When
764 this time the only mechanism to clear the usb-internal
765 wakeup-capability for an interface device is to unbind
768 Summary of poweroff pre-requisite settings relative to a port device::
772 echo auto > power/control # this is the default value
773 echo auto > <child>/power/control
777 -------------------------------------
793 all ports (set ``<hubdev-portX>/power/pm_qos_no_power_off`` to ``0``) when
796 ports when the screen blanks, and re-power them when the screen becomes