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

Rafael J. Wysocki
2012-04-01T07:18:59Z

Hi,

Sorry for the delayed response, I've been travelling recently.

On Sunday, April 01, 2012, Lin Ming wrote:
> On Sun, 2012-04-01 at 13:56 +0800, Aaron Lu wrote:
> > Hi,
> >
> > On Sun, Apr 01, 2012 at 01:27:33PM +0800, Lin Ming wrote:
> > > > - if (device->power.states[state].flags.explicit_set) {
> > > > + /* If state is D3 Cold, try to evaluate _PS3 first */
> > > > + if (state == ACPI_STATE_D3_COLD) {
> > > > + explicit_set = (ps - 1)->flags.explicit_set;
> > > > + object_name[3] -= 1;
> > > > + }
> > >
> > > I'm not sure whether this works or not.
> > >
> > > From ACPI spec,
> > >
> > > _PS3 "is used to put the specific device into its D3hot or D3 state"
> > >
> > > D3 neither means D3hot nor D3cold. It's an old term before D3hot and
> > > D3cold were introduced.
> > I guess D3 has to mean something, right? :-)

Well, not necessarily.

The problem is what state the _PS3 method puts the device into: D3_hot or
D3_cold.

Unfortunately, as far as I can say, ACPI 4.0 didn't specify any "official"
mapping between the "old" D3 and the "new" D3_{hod|cold} states, so we need to
figure out something. In my opinion, the only reasonable approach is to
assume that the state _PS3 puts the device into is always D3_cold, becuase
_PS3 may remove power completely from the device. It may not do that, but
we _must_ assume it does that in general.

> > Here is the problem, there is no _PR3 in AMD's implementation, just _PS3.
> > And since _S0W evaluates 4, I've to put this device into D3 cold state
> > with _PS3.
> >
> > 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

Exactly. What it means is basically "always reinitialize the device from
scratch if you have run _PS3 on it". And that's what we should do.

> > ------
> >
> > 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).
>
> But this is the generic code. We can't only consider some special
> device.
>
> Maybe we need some flag to tell which D3 state _PS3 is used for.

No, please. As I said above, we need to reinitialize devices that _PS3 was
executed on, which is equivalent to saying that those devices were put into
D3_cold.

The only situation where a device can be put into ACPI D3_hot (which is not
the same as PCI D3_hot, mind you) is when:

(1) There is _PR3 listing some of the device's power resources as "on".
(2) The power resources listed by the _PR3 as "off" are turned off and the
power resources listed by the _PR3 as "on" are left in the "on" state.

Our generic code should reflect that.

Thanks,
Rafael
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