• Rafael J. Wysocki's avatar
    PM: Asynchronous suspend and resume of devices · 5af84b82
    Rafael J. Wysocki authored
    Theoretically, the total time of system sleep transitions (suspend
    to RAM, hibernation) can be reduced by running suspend and resume
    callbacks of device drivers in parallel with each other.  However,
    there are dependencies between devices such that we're not allowed
    to suspend the parent of a device before suspending the device
    itself.  Analogously, we're not allowed to resume a device before
    resuming its parent.
    
    The most straightforward way to take these dependencies into accout
    is to start the async threads used for suspending and resuming
    devices at the core level, so that async_schedule() is called for
    each suspend and resume callback supposed to be executed
    asynchronously.
    
    For this purpose, introduce a new device flag, power.async_suspend,
    used to mark the devices whose suspend and resume callbacks are to be
    executed asynchronously (ie. in parallel with the main suspend/resume
    thread and possibly in parallel with each other) and helper function
    device_enable_async_suspend() allowing one to set power.async_suspend
    for given device (power.async_suspend is unset by default for all
    devices).  For each device with the power.async_suspend flag set the
    PM core will use async_schedule() to execute its suspend and resume
    callbacks.
    
    The async threads started for different devices as a result of
    calling async_schedule() are synchronized with each other and with
    the main suspend/resume thread with the help of completions, in the
    following way:
    (1) There is a completion, power.completion, for each device object.
    (2) Each device's completion is reset before calling async_schedule()
        for the device or, in the case of devices with the
        power.async_suspend flags unset, before executing the device's
        suspend and resume callbacks.
    (3) During suspend, right before running the bus type, device type
        and device class suspend callbacks for the device, the PM core
        waits for the completions of all the device's children to be
        completed.
    (4) During resume, right before running the bus type, device type and
        device class resume callbacks for the device, the PM core waits
        for the completion of the device's parent to be completed.
    (5) The PM core completes power.completion for each device right
        after the bus type, device type and device class suspend (or
        resume) callbacks executed for the device have returned.
    Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
    5af84b82
main.c 25.2 KB