Re: [PATCH v2 3/7] ACPI: Documentation: Document acpi_dev_state_d0()

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On Mon, Nov 20, 2023 at 10:31 AM Sakari Ailus
<sakari.ailus@xxxxxxxxxxxxxxx> wrote:
>
> Hi Laurent,
>
> On Sat, Nov 18, 2023 at 08:50:49PM +0200, Laurent Pinchart wrote:
> > Hi Sakari,
> >
> > Thank you for the patch.
> >
> > On Fri, Nov 17, 2023 at 01:14:29PM +0200, Sakari Ailus wrote:
> > > Document that acpi_dev_state_d0() can be used to tell if the device was
> > > powered on for probe.
> > >
> > > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > > ---
> > >  Documentation/firmware-guide/acpi/non-d0-probe.rst | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/Documentation/firmware-guide/acpi/non-d0-probe.rst b/Documentation/firmware-guide/acpi/non-d0-probe.rst
> > > index 7afd16701a02..815bcc8db69f 100644
> > > --- a/Documentation/firmware-guide/acpi/non-d0-probe.rst
> > > +++ b/Documentation/firmware-guide/acpi/non-d0-probe.rst
> > > @@ -24,6 +24,14 @@ there's a problem with the device, the driver likely probes just fine but the
> > >  first user will find out the device doesn't work, instead of a failure at probe
> > >  time. This feature should thus be used sparingly.
> > >
> > > +ACPI framework
> > > +--------------
> > > +
> > > +Use the Linux ACPI framework function :c:func:`acpi_dev_state_d0()` to tell
> > > +whether the device was powered on for probe. :c:func:`acpi_dev_state_d0()`
> > > +returns true if the device is powered on, false otherwise. For non-ACPI backed
> > > +devices it returns true always.
> > > +
> >
> > While this is true, I don't want to see drivers having to call
> > ACPI-specific functions, the same way you dislike OF-specific functions
> > in drivers. Please find a better way to handle this.
>
> The functionality is only available on ACPI and the function does the right
> thing on non-ACPI platforms. I don't see an issue here.

The issue would be calling an ACPI-specific function from code that's
otherwise firmware-agnostic, AFAICS.

It would be good to have a more generic way of checking whether or not
a device is operational.

> Feel free to post DT binding patches on suggested device power state during
> probe. :-) I think DT would benefit from this as well: the at24 driver is
> widely used and suddenly making probe() not talk to the chip (or even power
> it up) at all would probably be seen as a regression.

In the DT case it is more complicated, though, at least in general,
because there may be multiple clocks and regulators the device depends
on and you may need to toggle a GPIO line too.





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