Messages in this thread | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH 5] PM: Update comments describing device power management callbacks | Date | Mon, 21 Nov 2011 23:33:07 +0100 |
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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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