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

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Message-ID: <CAAhSdy3VBUTMg_b2tO12cTYuvHYtH=4dj9-qT-at35Whf3w_7w@mail.gmail.com>
Date:   Mon, 29 Jun 2020 09:39:24 +0530
From:   Anup Patel <anup@...infault.org>
To:     Zong Li <zong.li@...ive.com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/6] dt-bindings: riscv: Add YAML documentation for PMU

On Mon, Jun 29, 2020 at 8:49 AM Zong Li <zong.li@...ive.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@...ive.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@...ive.com>
> +  - Paul Walmsley <paul.walmsley@...ive.com>
> +  - Palmer Dabbelt <palmer@...belt.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.

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

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