Re: [PATCH v3 04/13] dt-bindings: x86: Add CPU bindings for x86

Ricardo Neri
2025-05-07T23:11:39Z

On Tue, May 06, 2025 at 09:25:59AM +0200, Krzysztof Kozlowski wrote:
> On Mon, May 05, 2025 at 09:52:35PM GMT, Ricardo Neri wrote:
> > On Sun, May 04, 2025 at 06:45:59PM +0200, Krzysztof Kozlowski wrote:
> > > On Sat, May 03, 2025 at 12:15:06PM GMT, Ricardo Neri wrote:
> > > > Add bindings for CPUs in x86 architecture. Start by defining the `reg` and
> > >
> > > What for?
> >
> > Thank you for your quick feedback, Krzysztof!
> >
> > Do you mean for what reason I want to start bindings for x86 CPUs? Or only
>
> Yes. For which devices, what purpose.

Sure, I could expand on this.

>
> > the `reg` property? If the former, it is to add an enable-method property to
> > x86 CPUs. If the latter, is to show the relationship between APIC and `reg`.
> >
> > >
> > > > `enable-method` properties and their relationship to x86 APIC ID and the
> > > > available mechanisms to boot secondary CPUs.
> > > >
> > > > Start defining bindings for Intel processors. Bindings for other vendors
> > > > can be added later as needed.
> > > >
> > > > Signed-off-by: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> > > > ---
> > >
> > > Not really tested so only limited review follows.
> >
> > Sorry, I ran make dt_binding_check but only on this schema. I missed the
> > reported error.
> >
> > >
> > > > .../devicetree/bindings/x86/cpus.yaml | 80 +++++++++++++++++++
> > > > 1 file changed, 80 insertions(+)
> > > > create mode 100644 Documentation/devicetree/bindings/x86/cpus.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/x86/cpus.yaml b/Documentation/devicetree/bindings/x86/cpus.yaml
> > > > new file mode 100644
> > > > index 000000000000..108b3ad64aea
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/x86/cpus.yaml
> > > > @@ -0,0 +1,80 @@
> > > > +# SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/x86/cpus.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: x86 CPUs
> > > > +
> > > > +maintainers:
> > > > + - Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
> > > > +
> > > > +description: |
> > > > + Description of x86 CPUs in a system through the "cpus" node.
> > > > +
> > > > + Detailed information about the CPU architecture can be found in the Intel
> > > > + Software Developer's Manual:
> > > > + https://intel.com/sdm
> > > > +
> > > > +properties:
> > > > + compatible:
> > > > + enum:
> > > > + - intel,x86
> > >
> > > That's architecture, not a CPU. CPUs are like 80286, 80386, so that's
> > > not even specific instruction set. I don't get what you need it for.
> >
> > Am I to understand the the `compatible` property is not needed if the
> > bindings apply to any x86 CPU?
>
> Every device needs compatible. Its meaning is explained:
> https://devicetree-specification.readthedocs.io/en/latest/chapter2-devicetree-basics.html#compatible
>
> If you add here a device representing CPU, then look at existing
> bindings for CPUs how they do it.
>
> It again feels like you add DT for platform which is not a real thing.

That is correct. I struggle to enumerate specific CPUs because the `intel,
wakeup-mailbox` enable method is implemented in the platform firmware and
is not tied to a given processor model as required by the rules of the
`compatible` property.

> If you use DT, you do not get different rules, therefore read all
> standard guides and tutorials (there were many, quite comprehensive).

I went through various materials. Perhaps I needed to understand the rules
better.

I realize now the DeviceTree is about describing hardware not firmware and
DT bindings are a suitable vehicle for this.

Thanks for the time you spent reviewing this patchset!

BR,
Ricardo