[PATCH RFC v3 01/21] ACPI: Only enumerate enabled (or functional) devices

[Rafael J. Wysocki]

On Mon, Jan 29, 2024 at 3:55 PM Russell King (Oracle)
<linux at armlinux.org.uk> wrote:
>
> Hi Jonathan,
>
> On Fri, Jan 12, 2024 at 11:52:05AM +0000, Jonathan Cameron wrote:
> > On Thu, 11 Jan 2024 10:26:15 +0000
> > "Russell King (Oracle)" <linux at armlinux.org.uk> wrote:
> > > @@ -2381,16 +2388,38 @@ EXPORT_SYMBOL_GPL(acpi_dev_clear_dependencies);
> > >   * acpi_dev_ready_for_enumeration - Check if the ACPI device is ready for enumeration
> > >   * @device: Pointer to the &struct acpi_device to check
> > >   *
> > > - * Check if the device is present and has no unmet dependencies.
> > > + * Check if the device is functional or enabled and has no unmet dependencies.
> > >   *
> > > - * Return true if the device is ready for enumeratino. Otherwise, return false.
> > > + * Return true if the device is ready for enumeration. Otherwise, return false.
> > >   */
> > >  bool acpi_dev_ready_for_enumeration(const struct acpi_device *device)
> > >  {
> > >     if (device->flags.honor_deps && device->dep_unmet)
> > >             return false;
> > >
> > > -   return acpi_device_is_present(device);
> > > +   /*
> > > +    * ACPI 6.5's 6.3.7 "_STA (Device Status)" allows firmware to return
> > > +    * (!present && functional) for certain types of devices that should be
> > > +    * enumerated. Note that the enabled bit should not be set unless the
> > > +    * present bit is set.
> > > +    *
> > > +    * However, limit this only to processor devices to reduce possible
> > > +    * regressions with firmware.
> > > +    */
> > > +   if (device->status.functional)
> > > +           return true;
>
> I have a report from within Oracle that this causes testing failures
> with QEMU using -smp cpus=2,maxcpus=4. I think it needs to be:
>
>         if (!device->status.present)
>                 return device->status.functional;
>
>         if (device->status.enabled)
>                 return true;
>
>         return !acpi_device_is_processor(device);

The above is fine by me.

> So we can better understand the history here, let's list it as a
> truth table. P=present, F=functional, E=enabled, Orig=how the code
> is in mainline, James=James' original proposal, Rafael=the proposed
> replacement but seems to be buggy, Rmk=the fixed version that passes
> tests:
>
> P F E   Orig    James   Rafael          Rmk
> 0 0 0   0       0       0               0
> 0 0 1   0       0       0               0
> 0 1 0   1       1       1               1
> 0 1 1   1       0       1               1
> 1 0 0   1       0       !processor      !processor
> 1 0 1   1       1       1               1
> 1 1 0   1       0       1               !processor
> 1 1 1   1       1       1               1
>
> Any objections to this?

So AFAIAC it can return false if not enabled, but present and
functional.  [Side note: I'm wondering what "functional" means then,
but whatever.]