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SubjectRe: [RFC PATCH 1/6] ACPI: Introduce ACPI D3_COLD state support
Date
On Tuesday, February 14, 2012, Zhang Rui wrote:
> Hi, Rafael,
>
> On 一, 2012-02-13 at 21:25 +0100, Rafael J. Wysocki wrote:
> > On Monday, February 13, 2012, Lin Ming wrote:
> > > From: Zhang Rui <rui.zhang@intel.com>
> > >
> > > If a device has _PR3._ON, it means the device supports D3_HOT.
> > > If a device has _PR3._OFF, it means the device supports D3_COLD.
> > > Add the ability to validate and enter D3_COLD state in ACPI.
> > >
> > > Signed-off-by: Zhang Rui <rui.zhang@intel.com>
> >
> > This is supposed to be ACPI 5.0 support, right?
> >
> No, D3_HOT is introduced in ACPI spec 4.0.
> According to the spec, _PR3 is used for devices that support both
> D3(D3_COLD) and D3HOT.

Yes, it does.

> The confusion here is that Linux D3 equals ACPICA D3HOT and Linux
> D3_COLD equals ACPICA D3.
> For example, when enter Linux ACPI D3, the reference count of ACPI Power
> Resources in _PR3 is increased by one.

That's correct.

> > So can anyone please tell me what part of the ACPI 5.0 spec is the
> > basis of this patch, because I can't see that immediately?
> >
> > The only places where D3Cold is _mentioned_ are Section 7.2.12 (_PRE, which
> > appears to be new in 5.0), Section 7.2.20 (_S0W), Section 7.2.21 (_S1W),
> > Section 7.2.22 (_S2W), Section 7.2.23 (_S3W) and Section 7.2.24 (_S4W).
> > None of them mentions those _PR3._ON and _PR3._OFF things above.
> >
> > Moreover, my understanding of the spec is that D3Cold means all of the
> > power resources returned by _PR3 are "off" (whereas some of them will be
> > "on" in D3hot).
> >
> Agreed.
>
> > > ---
> > > drivers/acpi/power.c | 4 ++--
> > > drivers/acpi/scan.c | 10 +++++++++-
> > > 2 files changed, 11 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/acpi/power.c b/drivers/acpi/power.c
> > > index 9ac2a9f..0d681fb 100644
> > > --- a/drivers/acpi/power.c
> > > +++ b/drivers/acpi/power.c
> > > @@ -500,14 +500,14 @@ int acpi_power_transition(struct acpi_device *device, int state)
> > > {
> > > int result;
> > >
> > > - if (!device || (state < ACPI_STATE_D0) || (state > ACPI_STATE_D3))
> > > + if (!device || (state < ACPI_STATE_D0) || (state > ACPI_STATE_D3_COLD))
> > > return -EINVAL;
> > >
> > > if (device->power.state == state)
> > > return 0;
> > >
> > > if ((device->power.state < ACPI_STATE_D0)
> > > - || (device->power.state > ACPI_STATE_D3))
> > > + || (device->power.state > ACPI_STATE_D3_COLD))
> > > return -ENODEV;
> > >
> > > /* TBD: Resources must be ordered. */
> > > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > > index 8ab80ba..a9d4391 100644
> > > --- a/drivers/acpi/scan.c
> > > +++ b/drivers/acpi/scan.c
> > > @@ -881,8 +881,16 @@ static int acpi_bus_get_power_flags(struct acpi_device *device)
> > >
> > > device->power.flags.power_resources = 1;
> > > ps->flags.valid = 1;
> > > - for (j = 0; j < ps->resources.count; j++)
> > > + for (j = 0; j < ps->resources.count; j++) {
> > > acpi_bus_add_power_resource(ps->resources.handles[j]);
> > > + /* Check for D3_COLD support. _PR3._OFF equals D3_COLD ? */
> > > + if (i == ACPI_STATE_D3) {
> > > + if (j == 0)
> > > + device->power.states[ACPI_STATE_D3_COLD].flags.valid = 1;
> > > + status = acpi_get_handle(ps->resources.handles[j], "_OFF", &handle);
> > > + device->power.states[ACPI_STATE_D3_COLD].flags.valid &= ACPI_SUCCESS(status);
> > > + }
> > > + }
> >
> > Sorry, but this doesn't make sense to me. Power resources always have
> > the _OFF method, right?
> >
> I'm not sure.

That would be explicitly against the spec that says that power resources
are *required* to have _ON, _OFF and _STA.

> I thought I had seen ACPI Power Resources without _OFF
> control method somewhere in bugzilla, but I can not find it out now.

That, clearly, is a firmware bug.

> Hmm, how about set D3_COLD support if _PR3 exists, but leave a warning
> message if _OFF doesn't exist, for now?

I don't think we need to set D3_COLD support at all. In fact, it is always
supported (as I said, if all power resources used by a device are off, the
device is in D3_COLD pretty much by definition).

Thanks,
Rafael
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