Lines Matching +full:system +full:- +full:management
1 .. _usb-power-management:
3 Power Management for USB
7 :Date: Last-updated: February 2014
11 ---------
12 * What is Power Management?
17 * Changing the default idle-delay time
19 * The driver interface for Power Management
23 * Interaction between dynamic PM and system PM
30 What is Power Management?
31 -------------------------
33 Power Management (PM) is the practice of saving energy by suspending
34 parts of a computer system when they aren't being used. While a
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
44 the system, we speak of it as a "system suspend". When a particular
45 device is turned off while the system as a whole remains running, we
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
67 ----------------------
85 --------------------------
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
123 We can categorize power management events in two broad classes:
125 agent outside the USB stack: system suspend/resume (triggered by
134 ---------------------------------
165 - ``on`` means that the device should be resumed and
166 autosuspend is not allowed. (Of course, system
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
228 Finally, the parameter value can be changed while the system is
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 --------
246 management. Nevertheless, the sad fact is that many devices do not
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
292 The driver interface for Power Management
293 -----------------------------------------
295 The requirements for a USB driver to support external power management
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 -----------------------------------
445 ``intf->needs_remote_wakeup`` to 1, the kernel won't autosuspend the
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
481 ----------------
483 For external events -- but not necessarily for autosuspend or
484 autoresume -- the device semaphore (udev->dev.sem) will be held when a
498 Interaction between dynamic PM and system PM
499 --------------------------------------------
501 Dynamic power management and system power management can interact in
504 Firstly, a device may already be autosuspended when a system suspend
505 occurs. Since system suspends are supposed to be as transparent as
506 possible, the device should remain suspended following the system
509 policy is to resume all devices during a system resume and let them
512 Secondly, a dynamic power-management event may occur as a system
513 suspend is underway. The window for this is short, since system
515 For example, a suspended device may send a remote-wakeup signal while
516 the system is suspending. The remote wakeup may succeed, which would
517 cause the system suspend to abort. If the remote wakeup doesn't
518 succeed, it may still remain active and thus cause the system to
519 resume as soon as the system suspend is complete. Or the remote
525 ---------------------
527 xHCI host controller provides hardware link power management to usb2.0
552 When a USB 3.0 lpm-capable device is plugged in to a
563 ----------------------
566 controlled link power management, the USB subsystem also has the
569 In the case of a root or platform-internal hub the host controller
589 goes through during system suspend, i.e. the power session is lost. Any
590 USB device or driver that misbehaves with system suspend will be
593 quirks) as the system resume path for the hub.
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
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
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::
777 -------------------------------------
793 all ports (set ``<hubdev-portX>/power/pm_qos_no_power_off`` to ``0``) when
795 system. For example, a distro may want to enable power off all USB
796 ports when the screen blanks, and re-power them when the screen becomes