Am Montag, 27. September 2004 22:16 schrieb Alan Stern:
> [I removed Patrick Mochel from the CC: list since he doesn't seem to be
> interested in this thread.]
>
> On Mon, 27 Sep 2004, David Brownell wrote:
>
> > > This should be subsumed under a policy setting such as PM_SNAPSHOT.
> >
> > Snapshotting is not a policy, it's an action involved in one kind of
> > system PM state change (not all of them).
>
> You're right, of course. I've been calling these things policy settings
> (not policies) but it would be good to have a more suitable term. "System
> power state" maybe -- although one of them is SELECTIVE_SUSPEND, which is
> hardly system-wide. It's also not clear to what extent these things refer
> to states or actions. Really they are both: requests to take action by
> preparing to change to a new state.
But snapshotting is a real system state. It has precisely defined
requirements.
-no DMA
-state in ram, not in device
You cannot translate it into a power stae, unfortunately.
> > > Drivers must understand that as meaning that the device should be idle
> > > (i.e., no DMA, no IRQs, and presumably in some known good state) and that
> > > when they resume from the SNAPSHOT a resume-from-disk may have intervened.
> >
> > I think it'd be fair to say that if a driver is really idle, then by
> > definition its state can be snapshotted. True equally of
> > polled (timer-driven?) or IRQ/DMA drivers.
>
> Idleness, as I'm using it here, is a property of devices, not drivers. It
> means specifically that the device isn't changing the contents of memory
> (DMA write), relying on the contents of memory (DMA read) or trying to
> change the flow of control (IRQ). It also means that the device is in
> some "good" state from which the driver can go back to normal operation,
> even if the device has lost power in the meantime.
And that the state is in ram. That's the whole point.
> > > That's right. Although it is appropriate to _use_ the driver model as a
> > > vehicle for allowing the user or other drivers to enable/disable/query
> > > wakeup settings.
> >
> > Only the policy settings, not the settings relating to hardware capability.
>
> I'm not sure what you mean here. As an example, a user would want to know
> whether a device supports remote wakeup. And the user might want to be
> able to specify whether or not remote wakeup should be disabled when the
> device is suspended.
Impossible to give generally. The answer would be a matrix of power
state and ability to do a remote wakeup.
Regards
Oliver
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