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    SubjectRe: [patch update] Re: [linux-pm] Run-time PM idea (was: Re: [RFC][PATCH 0/2] PM: Rearrange core suspend code)
    On Fri, 12 Jun 2009, Oliver Neukum wrote:

    > Am Freitag, 12. Juni 2009 04:16:10 schrieb Alan Stern:
    > > What tree constraint?  You mean that the PM core shouldn't allow
    > > devices to suspend unless all their children are suspended?  Why
    > > doesn't it still apply?
    >
    > Because the hardware doesn't need it.

    But maybe drivers need it.

    > > Remember, when Rafael and I say "suspend" here, we don't mean "go to a
    > > low-power state".  We mean "the PM core calls the runtime_suspend
    > > method".  No matter what actions the link hardware may decide to take
    > > on its own, the PM core will still want to observe the
    > > all-children-suspended restriction when calling runtime_suspend
    > > methods.
    >
    > No. The core if it insists all children be suspended will not use
    > the hardware's full capabilities.

    That isn't what I said. The core does not insist that all children be
    suspended, i.e., be in a low-power state. It insists only that the
    children's drivers' runtime_suspend methods have been called. Those
    methods are not obligated to put the children in a low-power state.

    > If it leaves such power saving measures to the drivers, latency
    > accounting will be wrong.
    >
    > > > I think there are devices who can be suspended while children are active
    > > > and devices which can not be. This is an attribute of the device and
    > > > should be evaluated by the core.
    > >
    > > Clearly it should be decided by the driver.  Should there be a bit for
    > > it in the dev_pm_info structure?
    >
    > Yes.

    That would resolve the issue.

    Alan Stern

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