Re: Re: uhci-hcd suspend/resume under the new driver model

[David Brownell <david-b-yBeKhBN/0LDR7s880joybQ@public.gmane.org>]

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On Monday 14 March 2005 11:30 am, Pavel Machek wrote:
> On Po 14-03-05 10:59:25, David Brownell wrote:
> 
> > > pci_choose_state() needs to return d3hot even 
> > > for pmsg_freeze, because that's what old code did, and I did not audit
> > > all the drivers.
> > 
> > Seems like a problem to me.  Do S1/S2/S3 transitions even
> > need a "freeze" transition?  I thought we'd agreed they don't;
> 
> That's not the problem.

It's _a_ problem, maybe not the one you want to focus on right now.


> Old code put devices into D3hot in swsusp "freeze" case. We'll need to
> do the same now, slowly auditing the drivers and removing that
> unneccessary D0->D3hot->D0 transition.

That's true.  The extra suspend/resume transition is trouble;
it's not necessary for the checkpoint stage, or system poweroff.


For the record, I've recently observed that all the swsusp issues
start making sense to me when I start thinking of swsusp as being
completely unrelated to suspend states.  (S4bios aside...)  And if
I don't think of it that way, I keep tripping over complications
where it's fighting against "real" suspend states.

The thing is, swsusp in normal usage does not involve system
suspend states like S1/S2/S3, or their analogues in non-ACPI
embedded systems.  Neither does it involve wakeup from those
states ... in fact, it fights against addressing all those.


If swsusp were called a system checkpoint/restore mechanism, it'd
have a much clearer relationship to power management:  enabling
system power-off is a useful side effect, but it's not exactly
the point of a checkpoint mechanism.  I suspect that if it were
packaged as halt-after-checkpoint, plus resume-from-checkpoint,
a lot of technical issues would start shaking out better.  Also
maybe some political/funding ones ... checkpointing has much
value for enterprise server operations.


OK, that's enough of a radical perspective for the moment.
I'm not sure I'll throw any more monkey wrenches today.  ;)

- Dave

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