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Date: Mon, 15 Apr 2024 16:48:54 +0100
From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
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Subject: Re: [PATCH v5 02/18] ACPI: processor: Set the ACPI_COMPANION for
 the struct cpu instance
Message-ID: <20240415164854.0000264f@Huawei.com>
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On Fri, 12 Apr 2024 20:10:54 +0200
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> On Fri, Apr 12, 2024 at 4:38=E2=80=AFPM Jonathan Cameron
> <Jonathan.Cameron@huawei.com> wrote:
> >
> > The arm64 specific arch_register_cpu() needs to access the _STA
> > method of the DSDT object so make it available by assigning the
> > appropriate handle to the struct cpu instance.
> >
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---
> >  drivers/acpi/acpi_processor.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processo=
r.c
> > index 7a0dd35d62c9..93e029403d05 100644
> > --- a/drivers/acpi/acpi_processor.c
> > +++ b/drivers/acpi/acpi_processor.c
> > @@ -235,6 +235,7 @@ static int acpi_processor_get_info(struct acpi_devi=
ce *device)
> >         union acpi_object object =3D { 0 };
> >         struct acpi_buffer buffer =3D { sizeof(union acpi_object), &obj=
ect };
> >         struct acpi_processor *pr =3D acpi_driver_data(device);
> > +       struct cpu *c;
> >         int device_declaration =3D 0;
> >         acpi_status status =3D AE_OK;
> >         static int cpu0_initialized;
> > @@ -314,6 +315,8 @@ static int acpi_processor_get_info(struct acpi_devi=
ce *device)
> >                         cpufreq_add_device("acpi-cpufreq");
> >         }
> >
> > +       c =3D &per_cpu(cpu_devices, pr->id);
> > +       ACPI_COMPANION_SET(&c->dev, device); =20
>=20
> This is also set for per_cpu(cpu_sys_devices, pr->id) in
> acpi_processor_add(), via acpi_bind_one().

Hi Rafael,

cpu_sys_devices gets filled with a pointer to this same structure.
The contents gets set in register_cpu() so at this point
it doesn't point anywhere.  As a side note register_cpu()
memsets to zero the value I set it to in the code above which isn't
great, particularly as I want to use this in post_eject for
arm64.

We could make a copy of the handle and put it back after
the memset in register_cpu() but that is also ugly.
It's the best I've come up with to make sure this is still set
come remove time but is rather odd.

>=20
> Moreover, there is some pr->id validation in acpi_processor_add(), so
> it seems premature to use it here this way.
>=20
> I think that ACPI_COMPANION_SET() should be called from here on
> per_cpu(cpu_sys_devices, pr->id) after validating pr->id (so the
> pr->id validation should all be done here) and then NULL can be passed
> as acpi_dev to acpi_bind_one() in acpi_processor_add().  Then, there
> will be one physical device corresponding to the processor ACPI device
> and no confusion.

I'm fairly sure this is pointing to the same device but agreed this
is a tiny bit confusing. However we can't use cpu_sys_devices at this point
so I'm not immediately seeing a cleaner solution :(

Jonathan

>=20
> >         /*
> >          *  Extra Processor objects may be enumerated on MP systems with
> >          *  less than the max # of CPUs. They should be ignored _iff
> > --
> > 2.39.2
> > =20