linux-kernel - Re: [PATCH v2] ACPI: D3 states cleanup

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Date:	Fri, 20 Apr 2012 13:12:54 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Aaron Lu <aaron.lu@....com>
Cc:	Lin Ming <ming.m.lin@...el.com>, Len Brown <lenb@...nel.org>,
	"linux-acpi" <linux-acpi@...r.kernel.org>,
	linux-kernel@...r.kernel.org, Zhang Rui <rui.zhang@...el.com>,
	"Huang, Ying" <ying.huang@...el.com>
Subject: Re: [PATCH v2] ACPI: D3 states cleanup

On Friday, April 20, 2012, Aaron Lu wrote:
> Hi,
> 
> On Fri, Apr 20, 2012 at 01:37:35PM +0800, Lin Ming wrote:
> > > > > > There are two ACPI D3 states defined now:
> > > > > > ACPI_STATE_D3 and ACPI_STATE_D3_COLD.
> > > > > > 
> > > > > > But the uses of these states are not clear/correct in some code.
> > > > > > For example, some code refer ACPI_STATE_D3 as D3hot and others refer
> > > > > > it as D3cold.
> > > > > > 
> > > > > > This patch introduces ACPI_STATE_D3_HOT to refer to ACPI D3hot state.
> > > > > > And changes ACPI_STATE_D3 to refer to ACPI D3cold state only.
> > > > > > Also redefines ACPI_STATE_D3_COLD the same as ACPI_STATE_D3.
> > > > > > 
> > > > > 
> > > > > With this patch now, if a device has _PS3, then we will set its D3hot
> > > > > flag valid. This doesn't feel right to me, since per our discussion the
> > > > > other day, we should assume _PS3 will put the device into D3cold.
> > > > > 
> > > > > Or do you mean: if _PS3 is available, then both D3hot and D3cold is
> > > > > valid from the perspective of acpi, it is the individual driver's
> > > > > responsibility to decide which state is actually valid and will be used.
> > > > 
> > > > Right.
> > > > 
> > > > ACPI_STATE_D3(same as ACPI_STATE_D3_COLD now) is always valid.
> > > > 
> > > 
> > > I mean, if _PS3 is available, can we say D3hot is valid?
> > 
> > Yes.
> > 
> 
> OK, now I'm confused...
> 
> First, let me try to clarify the meaning of acpi power state's valid
> flag.
> 
> By valid, I suppose it means the device can be in that state, instead of
> we have a way to program this device to go into that state.
> 
> e.g. D0 is valid means the device can be in D0 state, and D3_cold is
> valid means the device can be in D3_cold state. We unconditionally set
> these two states as valid, because we know every device supports these
> two states. But we might not be able to put the device into that state
> in software, since we might not have _PS0 or _PS3 control methods for it.
> 
> And if we do have the _PSx or _PRx control methods, we knows we have a
> way to put the device into that state, and hence the device should be
> able to support that power state, so we will set that state as valid too.
> 
> Is this correct?
> 
> For D3hot, obviously not all device supports this state, so we will need
> to figure it out through the acpi table.
> I remembered Rafael said the following words the other day in a reply to
> my evaluate_ps3_when_entering_d3_cold_patch:
> 
> -----------------------------------------------------------------------
> I'd rather say that with _PR3 we have the opportunity to avoid removing
> power completely from the device.  In other words, D3_hot is supported (and
> it is supported _only_ in that case).
> -----------------------------------------------------------------------
> 
> So I think here is a problem, that if a device has only _PS3, why should
> we say D3hot is supported? Is there a reason for this that I missed?

OK, I agree.  We need to special case the situation in which _PR3 is not
present, but _PS3 is.  IOW, we should do something like this in the loop in
acpi_bus_get_power_flags():


		/* State is valid if we have some power control */
		if (ps->resources.count
		    || (ps->flags.explicit_set && i < ACPI_STATE_D3))
			ps->flags.valid = 1;

Thanks,
Rafael
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