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SubjectRe: [PATCH 5] PM: Update comments describing device power management callbacks
Date
On Monday, November 21, 2011, Alan Stern wrote:
> On Mon, 21 Nov 2011, Rafael J. Wysocki wrote:
>
> > > > I said "Analogous to @suspend()" instead. I'm not sure why this is not
> > > > sufficient?
> > >
> > > Because @suspend() is very different! Its description basically says
> > > to do three things:
> > >
> > > Quiesce the device,
> > >
> > > Put it into a low-power state,
> > >
> > > And enable wakeup events.
> >
> > No, it doesn't any more. It's being changed by the proposed patch too. :-)
>
> I must have missed reading that part. Okay... but it seems weird that
> none of the new descriptions says anything about changing the power
> state. Shouldn't the description of @suspend say something like "For
> many platforms and subsystems, the device should be put in a low-power
> state"?

Hmm. I'm not really sure, actually, because I'd recommend that subsystems
rather than drivers change power states of devices and this description
is targeted at driver writers mostly.

> > > @freeze() is supposed to do the first but not the second or third.
> > > This makes it only 33% similar to @suspend(). :-)
> > >
> > > Also, the description of @suspend() says nothing about having a
> > > consistent memory image.
> >
> > Because that is irrelevant. The state of the device after the resume
> > has to be consistent, regardless of whether the resume is from RAM or
> > from an on-disk image.
>
> Sure, the device's state will be consistent. But will the contents of
> memory image be consistent? Not if the device was doing DMA writes
> during the time when the image was created.

Well, since .suspend() is also expected to stop DMA, that's rather moot.

Thanks,
Rafael


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