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SubjectRe: [RFC PATCH 4/6] PM / Runtime: Introduce flag can_power_off
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On Monday, February 13, 2012, 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).
>
> > > 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)?
>
> 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?
>
> Likewise, should new routines like pm_runtime_allow_power_off() be
> added to the runtime PM core if they are going to be used just by PCI?

No, they shouldn't.

Thanks,
Rafael


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