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    SubjectRe: [PATCH 0/8] Suspend block api (version 7)
    On Wednesday 19 May 2010, Arve Hjønnevåg wrote:
    > PM: Opportunistic suspend support.
    > Power management features present in the current mainline kernel are
    > insufficient to get maximum possible energy savings on some platforms,
    > such as Android. The problem is that to save maximum amount of energy
    > all system hardware components need to be in the lowest-power states
    > available for as long as reasonably possible, but at the same time the
    > system must always respond to certain events, regardless of the
    > current state of the hardware.
    > The first goal can be achieved either by using device runtime PM and
    > cpuidle to put all hardware into low-power states, transparently from
    > the user space point of view, or by suspending the whole system.
    > However, system suspend, in its current form, does not guarantee that
    > the events of interest will always be responded to, since wakeup
    > events (events that wake the CPU from idle and the system from
    > suspend) that occur right after initiating suspend will not be
    > processed until another possibly unrelated event wakes the system up
    > again.
    > On hardware where idle can enter the same power state as suspend, idle
    > combined with runtime PM can be used, but periodic wakeups increase
    > the average power consumption. Suspending the system also reduces the
    > harm caused by apps that never go idle. There also are systems where
    > some devices cannot be put into low-power states without suspending
    > the entire system (or the low-power states available to them without
    > suspending the entire system are substantially shallower than the
    > low-power states they are put into when the entire system is
    > suspended), so the system has to be suspended as a whole to achieve
    > the maximum energy savings.
    > To allow Android and similar platforms to save more energy than they
    > currently can save using the mainline kernel, introduce a mechanism by
    > which the system is automatically suspended (i.e. put into a
    > system-wide sleep state) whenever it's not doing work that's
    > immediately useful to the user, called opportunistic suspend.
    > For this purpose introduce the suspend blockers framework allowing the
    > kernel's power management subsystem to decide when it is desirable to
    > suspend the system (i.e. when the system is not doing anything the
    > user really cares about at the moment and therefore it may be
    > suspended). Add an API that that drivers can use to block
    > opportunistic suspend. This is needed to avoid losing wakeup events
    > that occur right after suspend is initiated.
    > Add /sys/power/policy that selects the behavior of /sys/power/state.
    > After setting the policy to opportunistic, writes to /sys/power/state
    > become non-blocking requests that specify which suspend state to enter
    > when no suspend blockers are active. A special state, "on", stops the
    > process by activating the "main" suspend blocker.

    That looks good to me.

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