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    Subject[PATCH 5/5] PM: Runtime PM documentation update
    From: Alan Stern <>

    This patch (as1318) updates the runtime PM documentation, adding a
    section discussing the interaction between runtime PM and system sleep.

    [rjw: Rebased and made it agree with the other updates better.]

    Signed-off-by: Alan Stern <>
    Signed-off-by: Rafael J. Wysocki <>
    Documentation/power/runtime_pm.txt | 50 +++++++++++++++++++++++++++++++++++++
    1 file changed, 50 insertions(+)

    Index: linux-2.6/Documentation/power/runtime_pm.txt
    --- linux-2.6.orig/Documentation/power/runtime_pm.txt
    +++ linux-2.6/Documentation/power/runtime_pm.txt
    @@ -381,3 +381,53 @@ incremented by the core before executing
    may be desirable to suspend the device as soon as ->probe() or ->remove() has
    finished, so the PM core uses pm_runtime_idle_sync() to invoke the
    subsystem-level idle callback for the device at that time.
    +6. Run-time PM and System Sleep
    +Run-time PM and system sleep (i.e., system suspend and hibernation, also known
    +as suspend-to-RAM and suspend-to-disk) interact with each other in a couple of
    +ways. If a device is active when a system sleep starts, everything is
    +straightforward. But what should happen if the device is already suspended?
    +The device may have different wake-up settings for run-time PM and system sleep.
    +For example, remote wake-up may be enabled for run-time suspend but disallowed
    +for system sleep (device_may_wakeup(dev) returns 'false'). When this happens,
    +the subsystem-level system suspend callback is responsible for changing the
    +device's wake-up setting (it may leave that to the device driver's system
    +suspend routine). It may be necessary to resume the device and suspend it again
    +in order to do so. The same is true if the driver uses different power levels
    +or other settings for run-time suspend and system sleep.
    +During system resume, devices generally should be brought back to full power,
    +even if they were suspended before the system sleep began. There are several
    +reasons for this, including:
    + * The device might need to switch power levels, wake-up settings, etc.
    + * Remote wake-up events might have been lost by the firmware.
    + * The device's children may need the device to be at full power in order
    + to resume themselves.
    + * The driver's idea of the device state may not agree with the device's
    + physical state. This can happen during resume from hibernation.
    + * The device might need to be reset.
    + * Even though the device was suspended, if its usage counter was > 0 then most
    + likely it would need a run-time resume in the near future anyway.
    + * Always going back to full power is simplest.
    +If the device was suspended before the sleep began, then its run-time PM status
    +will have to be updated to reflect the actual post-system sleep status. The way
    +to do this is:
    + pm_runtime_disable(dev);
    + pm_runtime_set_active(dev);
    + pm_runtime_enable(dev);
    +The PM core always increments the run-time usage counter before calling the
    +->prepare() callback and decrements it after calling the ->complete() callback.
    +Hence disabling run-time PM temporarily like this will not cause any run-time
    +suspend callbacks to be lost.

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