Re: [PATCH v2] dt-bindings: riscv: Fix CPU schema errors

Paul Walmsley
2019-10-10T18:35:01Z

On Thu, 10 Oct 2019, Rob Herring wrote:

> On Wed, Oct 9, 2019 at 7:08 PM Paul Walmsley <paul.walmsley@sifive.com> wrote:
> >
> > On Wed, 9 Oct 2019, Rob Herring wrote:
> >
> > > Fix the errors in the RiscV CPU DT schema:
> > >
> > > Documentation/devicetree/bindings/riscv/cpus.example.dt.yaml: cpu@0: 'timebase-frequency' is a required property
> > > Documentation/devicetree/bindings/riscv/cpus.example.dt.yaml: cpu@1: 'timebase-frequency' is a required property
> > > Documentation/devicetree/bindings/riscv/cpus.example.dt.yaml: cpu@0: compatible:0: 'riscv' is not one of ['sifive,rocket0', 'sifive,e5', 'sifive,e51', 'sifive,u54-mc', 'sifive,u54', 'sifive,u5']
> > > Documentation/devicetree/bindings/riscv/cpus.example.dt.yaml: cpu@0: compatible: ['riscv'] is too short
> > > Documentation/devicetree/bindings/riscv/cpus.example.dt.yaml: cpu@0: 'timebase-frequency' is a required property
> > >
> > > The DT spec allows for 'timebase-frequency' to be in 'cpu' or 'cpus' node
> > > and RiscV is doing nothing special with it, so just drop the definition
> > > here and don't make it required.
> >
> > The RISC-V kernel code does in fact parse it and use it, and we currently
> > rely on it being under /cpus:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/riscv/kernel/time.c#n19
> >
> > The RISC-V user ISA specification also constrains the timebase-frequency
> > to be the same across all CPUs, in section 10.1:
> >
> > https://github.com/riscv/riscv-isa-manual/releases/download/draft-20190608-f467e5d/riscv-spec.pdf
> >
> > So the right thing is to require 'timebase-frequency' at /cpus, and forbid
> > it in the individual CPU nodes.
>
> Yes, but this schema only deals with 'cpu' nodes and we can't check
> /cpus here. We'd need to write another schema matching on a child cpu
> node having a RiscV compatible.
>
> I can change this to 'timebase-frequency: false' to ban it here.

Sounds good to me. (Might catch the occasional mistake.) With that
change, the resulting patch would be

Acked-by: Paul Walmsley <paul.walmsley@sifive.com> # for arch/riscv

and thanks indeed for cleaning this up.

> That doesn't add too much as any undefined name is still allowed such as
> 'timbase-frequency'. There's a way to address this in json-schema draft8
> with 'unevaluatedProperties', but that's not ready yet.

OK

- Paul