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

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Date:   Wed, 25 Sep 2019 14:24:17 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     robh@...nel.org
CC:     Paul Walmsley <paul.walmsley@...ive.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org
Subject:     Re: [PATCH v2] dt-bindings: riscv: Fix CPU schema errors

On Wed, 25 Sep 2019 06:12:52 PDT (-0700), robh@...nel.org 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
>
> Fixes: 4fd669a8c487 ("dt-bindings: riscv: convert cpu binding to json-schema")
> Cc: Paul Walmsley <paul.walmsley@...ive.com>
> Cc: Palmer Dabbelt <palmer@...ive.com>
> Cc: Albert Ou <aou@...s.berkeley.edu>
> Cc: linux-riscv@...ts.infradead.org
> Signed-off-by: Rob Herring <robh@...nel.org>
> ---
> v2:
>  - Add timebase-frequency to simulator example.
>
>  .../devicetree/bindings/riscv/cpus.yaml       | 26 ++++++++++---------
>  1 file changed, 14 insertions(+), 12 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/riscv/cpus.yaml b/Documentation/devicetree/bindings/riscv/cpus.yaml
> index b261a3015f84..eb0ef19829b6 100644
> --- a/Documentation/devicetree/bindings/riscv/cpus.yaml
> +++ b/Documentation/devicetree/bindings/riscv/cpus.yaml
> @@ -24,15 +24,17 @@ description: |
>
>  properties:
>    compatible:
> -    items:
> -      - enum:
> -          - sifive,rocket0
> -          - sifive,e5
> -          - sifive,e51
> -          - sifive,u54-mc
> -          - sifive,u54
> -          - sifive,u5
> -      - const: riscv
> +    oneOf:
> +      - items:
> +          - enum:
> +              - sifive,rocket0
> +              - sifive,e5
> +              - sifive,e51
> +              - sifive,u54-mc
> +              - sifive,u54
> +              - sifive,u5
> +          - const: riscv
> +      - const: riscv    # Simulator only
>      description:
>        Identifies that the hart uses the RISC-V instruction set
>        and identifies the type of the hart.
> @@ -67,8 +69,6 @@ properties:
>        lowercase to simplify parsing.
>
>    timebase-frequency:
> -    type: integer
> -    minimum: 1
>      description:
>        Specifies the clock frequency of the system timer in Hz.
>        This value is common to all harts on a single system image.
> @@ -102,9 +102,9 @@ examples:
>      cpus {
>          #address-cells = <1>;
>          #size-cells = <0>;
> -        timebase-frequency = <1000000>;
>          cpu@0 {
>                  clock-frequency = <0>;
> +                timebase-frequency = <1000000>;
>                  compatible = "sifive,rocket0", "riscv";
>                  device_type = "cpu";
>                  i-cache-block-size = <64>;
> @@ -120,6 +120,7 @@ examples:
>          };
>          cpu@1 {
>                  clock-frequency = <0>;
> +                timebase-frequency = <1000000>;
>                  compatible = "sifive,rocket0", "riscv";
>                  d-cache-block-size = <64>;
>                  d-cache-sets = <64>;
> @@ -153,6 +154,7 @@ examples:
>                  device_type = "cpu";
>                  reg = <0>;
>                  compatible = "riscv";
> +                timebase-frequency = <1000000>;
>                  riscv,isa = "rv64imafdc";
>                  mmu-type = "riscv,sv48";
>                  interrupt-controller {

Looking at this spec

    https://github.com/devicetree-org/devicetree-specification/releases/download/v0.2/devicetree-specification-v0.2.pdf

section 3.7 says

    Properties that have identical values across cpu nodes may be placed in the 
    /cpus node instead. A client program must
    first examine a specific cpu node, but if an expected property is not found 
    then it should look at the parent /cpus node.
    This results in a less verbose representation of properties which are 
    identical across all CPUs.

I can never figure out if I'm looking at the right DT specifications so it's 
possible that is defunct, I just bring this up because we've got an outstanding 
bug in our port where we're not respecting what section 3.7 says and are only 
looking at /cpus/timebase-frequency instead of /cpus/cpu@...imebase-frequency, 
and I'm wondering if the fix should allow for looking at 
/cpus/timebase-frequency or just not bother.