linux-kernel - Re: [PATCH v3 1/2] dt-bindings: interrupt-controller: sifive,plic: Fix number of interrupts

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Date:   Fri, 17 Dec 2021 18:17:22 +0530
From:   Anup Patel <anup@...infault.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <maz@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Sagar Kadam <sagar.kadam@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        Rob Herring <robh@...nel.org>
Subject: Re: [PATCH v3 1/2] dt-bindings: interrupt-controller: sifive,plic:
 Fix number of interrupts

On Fri, Dec 17, 2021 at 6:04 PM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> The number of interrupts lacks an upper bound, thus assuming one,
> causing properly grouped "interrupts-extended" properties to be flagged
> as an error by "make dtbs_check".
>
> Fix this by adding the missing "maxItems".  As the architectural maximum
> is 15872 interrupts, using that as the limit would be unpractical.
> Hence limit it to 9 interrupts (one interrupt for a system management
> core, and two interrupts per core for other cores).  This should be
> sufficient for now, and the limit can always be increased when the need
> arises.

I disagree with having "maxItems" as 9.

We are in the process of increasing max CPUs supported by
QEMU virt machine to 512. There are already high CPU count
systems already announced (example SiFive P650 which will
have 16 cores). The "maxItems = 9" set by this patch will soon
be out-of-date.

The "maxItems" should represent PLIC spec constraints so
please don't add any synthetic value here.

Regards,
Anup

>
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> Acked-by: Rob Herring <robh@...nel.org>
> ---
> v3:
>   - Add Acked-by,
>
> v2:
>   - Split in two patches,
>   - Improve patch description and document limit rationale.
> ---
>  .../bindings/interrupt-controller/sifive,plic-1.0.0.yaml         | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
> index 28b6b17fe4b26778..0c6687511457413e 100644
> --- a/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
> +++ b/Documentation/devicetree/bindings/interrupt-controller/sifive,plic-1.0.0.yaml
> @@ -62,6 +62,7 @@ properties:
>
>    interrupts-extended:
>      minItems: 1
> +    maxItems: 9
>      description:
>        Specifies which contexts are connected to the PLIC, with "-1" specifying
>        that a context is not present. Each node pointed to should be a
> --
> 2.25.1
>