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

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Message-ID: <87y0p4xge9.ffs@tglx>
Date: Tue, 21 Oct 2025 20:23:58 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Troy Mitchell <troy.mitchell@...ux.dev>, 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
Subject: Re: [PATCH] irqchip/sifive-plic: use hartid as context_id in OF to
 fix AMP conflicts

On Tue, Oct 21 2025 at 09:14, Troy Mitchell wrote:
> On Mon, Oct 20, 2025 at 07:44:55PM +0200, Thomas Gleixner wrote:
>> 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?
> The issue still exists in the current driver.
> The PLIC driver for OF-based platforms assigns context_id = i inside
> the context loop, which assumes that all harts are numbered contiguously
> starting from 0.
>
> In AMP systems (e.g., when Linux boots from hart4 while hart0 runs another OS),
> this assumption breaks — multiple contexts from different clusters share the same
> enable_base(e.g., core4's enable_base = core0's enable_base), causing conflicts.
>
> This patch fixes the problem by assigning context_id based on the actual hartid,
> ensuring that each hart context maps to a unique enable region,
> while preserving behavior on SMP and UP systems.
>
> Does it make sense? I'll update my commit message in the next version.

Yes. Though this still applies:
 
>> # git grep 'This patch' Documentation/process/

Thanks,

        tglx