[RFC PATCH 1/6] dt-bindings: riscv: Add YAML documentation for PMU

[Zong Li]

On Mon, Jun 29, 2020 at 12:09 PM Anup Patel <anup at brainfault.org> wrote:
>
> On Mon, Jun 29, 2020 at 8:49 AM Zong Li <zong.li at sifive.com> wrote:
> >
> > Add device tree bindings for performance monitor unit. And it passes the
> > dt_binding_check verification.
> >
> > Signed-off-by: Zong Li <zong.li at sifive.com>
> > ---
> >  .../devicetree/bindings/riscv/pmu.yaml        | 59 +++++++++++++++++++
> >  1 file changed, 59 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/riscv/pmu.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/riscv/pmu.yaml b/Documentation/devicetree/bindings/riscv/pmu.yaml
> > new file mode 100644
> > index 000000000000..f55ccbc6c685
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/riscv/pmu.yaml
> > @@ -0,0 +1,59 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/riscv/pmu.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: RISC-V Performance Monitor Units
> > +
> > +maintainers:
> > +  - Zong Li <zong.li at sifive.com>
> > +  - Paul Walmsley <paul.walmsley at sifive.com>
> > +  - Palmer Dabbelt <palmer at dabbelt.com>
> > +
> > +properties:
> > +  compatible:
> > +    items:
> > +      - const: riscv,pmu
> > +
> > +  riscv,width-base-cntr:
> > +    description: The width of cycle and instret CSRs.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +
> > +  riscv,width-event-cntr:
> > +    description: The width of hpmcounter CSRs.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
>
> The terms "base" and "event" is confusing because
> we only have counters with no interrupt associated with it.
>
> The RISC-V spec defines 3 counters and rest are all
> implementation specific counters.

As I know, there are 2 counters of spec definition: cycle and instret.
What is the 3rd counter you mentioned?

>
> I suggest using the terms "spec counters" and "impl counters"
> instead of "base counters" and "event counters".

OK, they are good to me. Let me change it.


>
> Further, "riscv,width" properties are redundant because
> RISC-V spec clearly tells that counters are 64bit for both
> RV32 and RV64.
>
> > +
> > +  riscv,n-event-cntr:
> > +    description: The number of hpmcounter CSRs.
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +
> > +  riscv,hw-event-map:
> > +    description: The mapping of generic hardware events. Default is no mapping.
> > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > +
> > +  riscv,hw-cache-event-map:
> > +    description: The mapping of generic hardware cache events.
> > +      Default is no mapping.
> > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > +
> > +required:
> > +  - compatible
> > +  - riscv,width-base-cntr
> > +  - riscv,width-event-cntr
> > +  - riscv,n-event-cntr
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    pmu {
> > +      compatible = "riscv,pmu";
> > +      riscv,width-base-cntr = <64>;
> > +      riscv,width-event-cntr = <40>;
> > +      riscv,n-event-cntr = <2>;
> > +      riscv,hw-event-map = <0x0 0x0 0x1 0x1 0x3 0x0202 0x4 0x4000>;
> > +      riscv,hw-cache-event-map = <0x010201 0x0102 0x010204 0x0802>;
> > +    };
> > +
> > +...
> > --
> > 2.27.0
> >
>
> Regards,
> Anup