Re: [PATCH v9 1/7] ACPI: scan: Obtain device's desired enumeration power state

[Sakari Ailus]

Hi Rafael,

Thanks for the comments.

On Fri, Jan 29, 2021 at 03:07:57PM +0100, Rafael J. Wysocki wrote:
> On Fri, Jan 29, 2021 at 12:27 AM Sakari Ailus
> <sakari.ailus@xxxxxxxxxxxxxxx> wrote:
> >
> > Store a device's desired enumeration power state in struct
> > acpi_device_power_flags during acpi_device object's initialisation.
> >
> > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > ---
> >  drivers/acpi/scan.c     | 6 ++++++
> >  include/acpi/acpi_bus.h | 3 ++-
> >  2 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > index 1d7a02ee45e05..b077c645c9845 100644
> > --- a/drivers/acpi/scan.c
> > +++ b/drivers/acpi/scan.c
> > @@ -987,6 +987,8 @@ static void acpi_bus_init_power_state(struct acpi_device *device, int state)
> >
> >  static void acpi_bus_get_power_flags(struct acpi_device *device)
> >  {
> > +       unsigned long long pre;
> > +       acpi_status status;
> >         u32 i;
> >
> >         /* Presence of _PS0|_PR0 indicates 'power manageable' */
> > @@ -1008,6 +1010,10 @@ static void acpi_bus_get_power_flags(struct acpi_device *device)
> >         if (acpi_has_method(device->handle, "_DSW"))
> >                 device->power.flags.dsw_present = 1;
> >
> > +       status = acpi_evaluate_integer(device->handle, "_PRE", NULL, &pre);
> > +       if (ACPI_SUCCESS(status) && !pre)
> > +               device->power.flags.allow_low_power_probe = 1;
> 
> While this is what has been discussed and thanks for taking it into
> account, I'm now thinking that it may be cleaner to introduce a new
> object to return the deepest power state of the device in which it can
> be enumerated, say _DSE (Device State for Enumeration) such that 4
> means D3cold, 3 - D3hot and so on, so the above check can be replaced
> with something like
> 
> status = acpi_evaluate_integer(device->handle, "_PRE", NULL, &dse);

s/_PRE/_DSE/

?

> if (ACPI_FAILURE(status))

ACPI_SUCCESS?

>         device->power.state_for_enumeratin = dse;
> 
> And then, it is a matter of comparing ->power.state_for_enumeratin
> with ->power.state and putting the device into D0 if the former is
> shallower than the latter.
> 
> What do you think?

Sounds good. How about calling the function e.g.
acpi_device_resume_for_probe(), so runtime PM could be used to resume the
device if the function returns true?

-- 
Kind regards,

Sakari Ailus