linux-kernel - Re: [PATCH] ACPI: evaluate

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Message-ID: <20120401153434.GA3268@localhost.amd.com>
Date:	Sun, 1 Apr 2012 23:34:35 +0800
From:	Aaron Lu <aaron.lu@....com>
To:	Zhang Rui <rui.zhang@...el.com>
CC:	Lin Ming <ming.m.lin@...el.com>, Len Brown <lenb@...nel.org>,
	"Rafeal J. Wysocki" <rjw@...k.pl>, <linux-acpi@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Andiry Xu <andiry.xu@....com>, Alex He <alex.he@....com>
Subject: Re: [PATCH] ACPI: evaluate _PS3 when entering D3 Cold

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.

> 
> > 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.

-Aaron


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