linux-kernel - Re: [PATCH] irqchip/sifive-plic: use hartid as context

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Message-ID: <87bjm1zcvc.ffs@tglx>
Date: Mon, 20 Oct 2025 19:44:55 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Troy Mitchell <troy.mitchell@...ux.dev>, Paul Walmsley <pjw@...nel.org>,
 Samuel Holland <samuel.holland@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti
 <alex@...ti.fr>
Cc: linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org, Troy
 Mitchell <troy.mitchell@...ux.dev>
Subject: Re: [PATCH] irqchip/sifive-plic: use hartid as context_id in OF to
 fix AMP conflicts

On Mon, Oct 20 2025 at 11:49, Troy Mitchell wrote:
> In asymmetric multi-processing (AMP) scenarios, the original PLIC
> driver used the context loop index 'i' as context_id for OF (device

Which original driver and when did it stop to use the context loop index?

> tree) platforms. This caused multiple contexts from different harts
> (e.g., core0 and core4) to share the same enable_base, leading to
> conflicts when initializing the PLIC.

When did it stop to cause the issues? And if the issues have been
already resolved, what is this patch about?

> This patch resolves enable_base conflicts on AMP platforms while

# git grep 'This patch' Documentation/process/

> maintaining SMP/UP behavior.

There is zero explanation what this patch does to resolve the issue.

See also:

  https://www.kernel.org/doc/html/latest/process/maintainer-tip.html#changelog

>  
>  		if (is_of_node(fwnode)) {
> -			context_id = i;
> +			context_id = hartid * 2 + i % 2;

This is incomprehensible and will cause head scratching 6 weeks down the
road. This needs a proper comment with an explanation what this is
about and why it is correct under all circumstances.

Thanks,

        tglx