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    SubjectRe: [RFC PATCH 4/6] PM / Runtime: Introduce flag can_power_off
    On Tuesday, February 21, 2012, Zhang Rui wrote:
    > On 二, 2012-02-21 at 00:13 +0100, Rafael J. Wysocki wrote:
    > > > So how to handle this case, say, for a device in the generic PM domain
    > > > that supports 2 different low power state, D1 and D2.
    > > > D2 is deeper than D1, and it is kind of cold power off with remote
    > > > wakeup disabled. If the driver needs to runtime suspend the device with
    > > > remote wakeup enabled, it should set the device to D1, but it can not
    > > > set the RPM_SUSPEND?
    > >
    > > The device is regarded as "suspended" if its bus type's (or PM domain's)
    > > .runtime_suspend() callback has been executed and has returned 0 (success).
    > > What the callback has actually done is not of any interest to the core.
    > >
    > right.
    > > Now, the D1 and D2 case has to be handled by the bus (PM domain) and
    > > driver. In both cases the device will be regarded as "suspended" and the
    > > core doesn't track the actual device state.
    > >
    > > I think the problem here is that the PCI bus type's runtime PM callbacks
    > > aren't very sophisticated (they just choose the lowest possible low-power
    > > state and attempt to put the device into it) and I can see two possible
    > > ways to address that.
    > >
    > > First, you can modify pci_pm_runtime_suspend/_resume() to handle multiple
    > > states (for example, to choose the target low-power state more intelligently
    > > than they do right now). Second, you can add a PM domain that will do what
    > > you want from pci_pm_runtime_suspend/_resume() for a specific set of devices.
    > >
    > But RPM_SUSPENDED is set by PM core after .runtime_suspend() being
    > invoked, even if device is in D1 instead of D2, right?
    > So the problem is that, if a device in a generic power domain supports
    > two low power state, one is compatible with generic power domain power
    > off and another is not, how can the device driver pass this information
    > to the generic power domain, i.e. how to runtime suspend a device while
    > keep the generic power domain always on?

    There are two "low-power" levels in the generic PM domains framework. The
    first one is the per-device low-power in which devices are put into their
    individual (programmable) low-power states by the domain .dev_ops->stop()
    callback. The second one is when .stop() has been called for all devices,
    so presumably all of them are in programmable low-power states and it's
    possible to switch the entire domain off. This is done by the domain
    .power_off() callback.

    It seems that the trick might be to make .dev_ops->stop() avoid turning off
    power resources for the last suspending device in the domain and leave that
    to domain .power_off().

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