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    SubjectRe: [RFC PATCH 4/6] PM / Runtime: Introduce flag can_power_off
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    Hi, Alan,

    On 一, 2012-02-13 at 15:41 -0500, Alan Stern wrote:
    > On Mon, 13 Feb 2012, Rafael J. Wysocki wrote:
    >
    > > > I'm not sure if this is really the right approach. What you're trying
    > > > to do is implement two different low-power states, basically D3hot and
    > > > D3cold. Currently the runtime PM core doesn't support such things; all
    > > > it knows about is low power and full power.
    > >
    > > I'd rather say all it knows about is "suspended" and "active", which mean
    > > "the device is not processing I/O" and "the device may be processing I/O",
    > > respectively. A "suspended" device may or may not be in a low-power state,
    > > but the runtime PM core doesn't care about that.
    >
    > Yes, okay. We can say that this patch tries to implement two different
    > "suspended" states, basically "low power" and "power off" (or D3hot and
    > D3cold).
    >
    Right!

    > > > Before doing an ad-hoc implementation, it would be best to step back
    > > > and think about other subsystems. Other sorts of devices may well have
    > > > multiple low-power states. What's the best way for this to be
    > > > supported by the PM core?
    > >
    > > Well, I honestly don't think there's any way they all can be covered at the
    > > same time and that's why we chose to support only "suspended" and "active"
    > > as defined above. The handling of multiple low-power states must be
    > > implemented outside of the runtime PM core (like in the PCI core, for example).
    >
    > That's the point. If this is to be implemented outside of the runtime
    > PM core, should the patch be allowed to add new fields to struct
    > dev_pm_info (which has to be shared among all subsystems)?
    >
    Surely it shouldn't in this case.

    > Or to put it another way, if we do add new fields to struct dev_pm_info
    > (like can_power_off) in order to help support multiple "suspended"
    > states, shouldn't these new fields be such that they can be used by
    > many different subsystems rather than being special for the
    > full-power/no-power situation?
    >
    My opinion is that the concept of "no-power state" is unique for all
    devices/buses/platforms.
    If any of them support this, they can use the routines without any
    confusion.

    thanks,
    rui

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