linux-kernel - Re: [PATCH v3 2/2] dt-bindings: perf: starfive: Add StarLink PMU

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Message-ID: <20231115-landing-earflap-ed11982ac610@squawk>
Date:   Wed, 15 Nov 2023 20:03:53 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Ji Sheng Teoh <jisheng.teoh@...rfivetech.com>
Cc:     Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Ley Foon Tan <leyfoon.tan@...rfivetech.com>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/2] dt-bindings: perf: starfive: Add StarLink PMU

Yo,

On Wed, Nov 15, 2023 at 11:36:08AM +0800, Ji Sheng Teoh wrote:
> Add device tree binding for StarFive's StarLink PMU (Performance
> Monitor Unit).
> 
> Signed-off-by: Ji Sheng Teoh <jisheng.teoh@...rfivetech.com>
> ---
>  .../bindings/perf/starfive,starlink-pmu.yaml  | 46 +++++++++++++++++++
>  1 file changed, 46 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/perf/starfive,starlink-pmu.yaml
> 
> diff --git a/Documentation/devicetree/bindings/perf/starfive,starlink-pmu.yaml b/Documentation/devicetree/bindings/perf/starfive,starlink-pmu.yaml
> new file mode 100644
> index 000000000000..a9426a7faeae
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/perf/starfive,starlink-pmu.yaml

btw, since you changed the compatible, the filename should have been
changed to match it.

> @@ -0,0 +1,46 @@
> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/perf/starfive,starlink-pmu.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: StarFive StarLink PMU
> +
> +maintainers:
> +  - Ji Sheng Teoh <jisheng.teoh@...rfivetech.com>
> +
> +description:
> +  StarFive's StarLink PMU integrates one or more CPU cores with a shared L3
> +  memory system. The PMU support overflow interrupt, up to 16 programmable
> +  64bit event counters, and an independent 64bit cycle counter.
> +  StarLink PMU is accessed via MMIO.
> +
> +properties:
> +  compatible:
> +    const: starfive,starlink-500-pmu

So this is not what I had in mind by a "device". I was looking for a
compatible representing an soc in which this IP had been integrated.
A soc-specific compatible, rather than something generic, is requirement
for devicetree - we don't want various integrations of this IP to all be
using a generic compatible when there may be subtle (or less subtle)
differences between integrations.

I'm trying to come up with the syntax for enforcing having two
compatibles with your current one as the fallback, but I have yet to
come up with the correct syntax for that that works correctly.

Hopefully by the time you get some feedback on the driver side of this
submission I will have a concrete suggestion for what to do here.

> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts:
> +    maxItems: 1
> +
> +required:
> +  - compatible
> +  - reg
> +  - interrupts
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    soc {
> +        #address-cells = <2>;
> +        #size-cells = <2>;
> +
> +        l3_pmu: pmu@...00000 {

This label here is never used and should be dropped.

Cheers.
Conor.

> +            compatible = "starfive,starlink-500-pmu";
> +            reg = <0x0 0x12900000 0x0 0x10000>;
> +            interrupts = <34>;
> +        };
> +    };
> -- 
> 2.25.1
> 

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