On Thu, 21 Feb 2008, Rafael J. Wysocki wrote:
>
> In fact we have acpi_pci_choose_state() that tells the driver which power
> state to put the device into in ->suspend(). If that is used, the device ends
> up in the state expected by to BIOS for S4.
First off, nobody should *ever* use that directly anyway.
Secondly, the one that people should use ("pci_choose_state()") doesn't
actually do what you claim it does. It does all kinds of wrong things, and
doesn't even take the target state into account at all. So look again.
> No. Again, if there are devices that wake us up from S4, but not from S5,
> they need to be handled differently in the *enter S4* case (hibernation) and
> in the *enter S5* case (powering off the system).
And again, what does this have to do with (the example I used) the
graphics hardware? Answer: nothing. The example I gave you we simply DO
THE WRONG THING FOR.
Same thing for things like USB devices - where pci_choose_state() doesn't
work to begin with. Why do we call "suspend()" on such a thing when we
don't want to suspend it? We shouldn't. We should call "freeze/unfreeze"
(which are no-ops) and then finally perhaps "poweroff", and that final
stage might want to spin things down or similar.
But *none* of it has anything to do with suspend, and none of it has
anything to do with pci_choose_state() (much less acpi_pci_choose_state)
The fact is, we should let the driver decide, and we should make it clear
to the driver writer what he is deciding about - rather than basically lie
and say "suspend the device and put it into D3" even when that's the last
thing it should ever do.
Linus
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