Re: [PATCH 1/6] ACPI: D3cold state is always valid

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Thursday, April 19, 2012, huang ying wrote:
> On Thu, Apr 19, 2012 at 5:13 AM, Rafael J. Wysocki <rjw@sisk.pl> wrote:
> > On Tuesday, April 17, 2012, huang ying wrote:
> >> On Tue, Apr 17, 2012 at 1:47 PM, Lin Ming <ming.m.lin@intel.com> wrote:
> >> > ACPI_STATE_D3 actually means ACPI D3hot which is not always valid.
> >> > Instead, ACPI D3cold is always valid.
> >> >
> >> > Signed-off-by: Lin Ming <ming.m.lin@intel.com>
> >> > ---
> >> >  drivers/acpi/scan.c |   11 ++---------
> >> >  1 files changed, 2 insertions(+), 9 deletions(-)
> >> >
> >> > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> >> > index 767e2dc..fb56388 100644
> >> > --- a/drivers/acpi/scan.c
> >> > +++ b/drivers/acpi/scan.c
> >> > @@ -884,13 +884,6 @@ static int acpi_bus_get_power_flags(struct acpi_device *device)
> >> >                                acpi_bus_add_power_resource(ps->resources.handles[j]);
> >> >                }
> >> >
> >> > -               /* The exist of _PR3 indicates D3Cold support */
> >> > -               if (i == ACPI_STATE_D3) {
> >> > -                       status = acpi_get_handle(device->handle, object_name, &handle);
> >> > -                       if (ACPI_SUCCESS(status))
> >> > -                               device->power.states[ACPI_STATE_D3_COLD].flags.valid = 1;
> >> > -               }
> >> > -
> >> >                /* Evaluate "_PSx" to see if we can do explicit sets */
> >> >                object_name[2] = 'S';
> >> >                status = acpi_get_handle(device->handle, object_name, &handle);
> >> > @@ -908,8 +901,8 @@ static int acpi_bus_get_power_flags(struct acpi_device *device)
> >> >        /* Set defaults for D0 and D3 states (always valid) */
> >> >        device->power.states[ACPI_STATE_D0].flags.valid = 1;
> >> >        device->power.states[ACPI_STATE_D0].power = 100;
> >> > -       device->power.states[ACPI_STATE_D3].flags.valid = 1;
> >> > -       device->power.states[ACPI_STATE_D3].power = 0;
> >> > +       device->power.states[ACPI_STATE_D3_COLD].flags.valid = 1;
> >> > +       device->power.states[ACPI_STATE_D3_COLD].power = 0;
> >> >
> >> >        acpi_bus_init_power(device);
> >>
> >> I think D3_HOT should be always valid, while D3_COLD should be valid
> >> for some situation.
> >
> > This need not be PCI, mind you.
> >
> >>  - has _PS3, no _PR3
> >>    - support D3_HOT, D3_COLD
> >
> > Nope.  D3_HOT cannot be supported in that case at the ACPI level.
> >
> >>    - set state
> >>      - D3_HOT: do nothing in ACPI
> >
> > That is not D3_HOT, then, from the ACPI point of view.  It is a different
> > power state.
> >
> > Suppose you have a non-PCI device that can be only power-manageable via ACPI
> > and that device has only _PS0 and _PS3.  How would you put it into D3_HOT,
> > in particular?
> 
> Normally, we will put it into D3_COLD (via _PS3).
> 
> If it is prevented to be put in D3_COLD,
>   - If D3_HOT is not marked as supported, we will keep it in D0
>   - otherwise, we advocate we put it into D3_HOT, but in fact, it is in D0.
> 
> The result is same, but with wrong name.
> 
> But there will be some real problem if we have something like CPU
> governor.  Because governor may choose D3_HOT for device.

In that case the ACPI layer should simply return an error code indicating
that the requested state is not available _from_ _it_.  If there are
more layers, however, they may be able to change the power state of
the device.

> But for PCI device, D3_HOT is supported for the device.

Yes, if the device supports native PM.  However, PCI D-states and ACPI D-states
are different things.  We kind of combine them in our PCI bus type.

> So the bus layer should combine the information from native power
> state supported and ACPI power state supported to determine which
> power states are supported?

Yes, we do that all the time, with the exception of D3 cold/hot.

> For example, for a PCI device, ACPI advocates D0 and D3_COLD are supported,
> and PCI layer may advocate D0, D3_HOT and D3_COLD are supported.

Exactly.  All of the available power states of the device depend on both
the device's own capabilities (ie. what PCI D-states the device may be
programmed into by register writes) and whatever is available from ACPI.

On embedded systems there are other factors as well.

Thanks,
Rafael