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

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Message-ID: <CAF1ivSYxoN3dbrNztY4BGLFYg6wGvCyypLgwXuOFam7uKtBB1w@mail.gmail.com>
Date:	Fri, 20 Apr 2012 23:14:40 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Aaron Lu <aaron.lu@....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 Fri, Apr 20, 2012 at 7:12 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> 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;

Will add below change.

-               /* State is valid if we have some power control */
-               if (ps->resources.count || ps->flags.explicit_set)
+               /*
+                * State is valid if we have some power control
+                * D3hot state is only valid if _PR3 present
+                */
+               if (ps->resources.count ||
+                   (ps->flags.explicit_set && i < ACPI_STATE_D3_HOT))
                        ps->flags.valid = 1;

Rafael,

can I still add your ACK when send updated patch?

Thanks,
Lin Ming

>
> Thanks,
> Rafael
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