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

From: Anup Patel
Date: Mon Jun 29 2020 - 17:05:27 EST


On Mon, Jun 29, 2020 at 8:49 AM Zong Li <zong.li@xxxxxxxxxx> wrote:
>
> Add device tree bindings for performance monitor unit. And it passes the
> dt_binding_check verification.
>
> Signed-off-by: Zong Li <zong.li@xxxxxxxxxx>
> ---
> .../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@xxxxxxxxxx>
> + - Paul Walmsley <paul.walmsley@xxxxxxxxxx>
> + - Palmer Dabbelt <palmer@xxxxxxxxxxx>
> +
> +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