Re: [PATCH] ACPI: evaluate _PS3 when entering D3 Cold

Rafael J. Wysocki
2012-04-01T07:43:06Z

On Sunday, April 01, 2012, Aaron Lu wrote:
> Hi,
>
> On Sun, Apr 01, 2012 at 03:03:39PM +0800, Zhang Rui wrote:
> > First of all, I agree that we must evaluate _PS3 when setting device to
> > either D3_HOT or D3_COLD.
> Good.
>
> >
> > And here is my understanding about D3/D3_HOT/D3_COLD,
> >
> > if _PR3 exists, it means the devices supports both D3_HOT and D3_COLD.
> Agree.
>
> >
> > if only _PS3 exists, we can only say that the state after evaluating
> > _PS3 is D3, it could either be D3_HOT or D3_COLD, and this is device
> > specific, which in your case, is D3_COLD.
> I prefer Rafeal's definition, let's just *assume* the device is at D3
> cold after its _PS3 is executed. Unless it has _PR3, in which case, we
> have a chance to put the device into D3 hot instead.
>
> >
> > BTW, here is the description of _S0W in ACPI spec,
> > If OSPM has not indicated that it supports _PR3 through the OSPM
> > Platform-Wide Capabilities (see Section 6.2.10.2), then the value "3"
> > corresponds to D3. If it has indicated _PR3 support, the value "3"
> > represents D3hot and the value "4" represents D3cold.
> >
> > So IMO, the _S0W should return 3 in AMD's implementation as it does not
> > have _PR3.
> OK, sounds like a firmware bug.
> Thanks for identifying this.

I don't think this is a bug. It actually may return either 3 or 4, because
there is no difference between them if there's no _PR3 (i.e. the action to
carry out by software would only be different if _PR3 were present).

> > > And the ACPI does have some words like:
> > >
> > > ------
> > > Platform/drivers must assume that the device will have power completely
> > > removed when the device is place into “D3” via _PS3
> > > ------
> > >
> > I think this means OS can not access device any more after evaluating
> > _PS3, and it should re-enumerate the device when transiting back to D0.
> >
> > > This is in section 7.2.11: _PR3.
> > >
> > > >
> > > > Another problem:
> > > >
> > > > With your patch, both D3hot and D3cold will evaluate _PS3, right?
> > > >
> > > Yes.
> > >
> > > > Will it have problem on AMD platform if you try to put ODD into D3hot
> > > > state? _PS3 is evaluated, so it actually enters D3Cold state.
> > >
> > > There is no D3 hot support for this device(from the firmware's
> > > perspective), either it is at D0(via _PS0), or it will be at D3 cold(via
> > > _PS3).
> > >
> > I was trying to make a cleanup of the D3/D3_HOT/D3_COLD support in
> > Linux, and this gives me some clue.
> This is great, and I would like to help as much as I can.
>
> >
> > How about this?
> >
> > We should use the term "D3" in general in Linux.
> > Without _PR3, OS should *assume* that the power is removed, although it
> > may be not true.
> > With _PR3, OS can *assure* that the power is removed, because it knows
> > how to remove thw power (evaluating _PR3._OFF).
> >
> > So the difference is that OS need to make sure whether to evaluate
> > _PR3._OFF when _PR3 exists. For example, a device has _PR3, but _S0W
> > returns 3, OS should not evaluate _PR3._OFF when the device sleeps with
> > remote wakeup support.
> >
> > what do you think?
> I agree with Rafeal's ideas.

Good. :-)

Thanks,
Rafael
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