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

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Message-ID: <aPnGsbufM1OwiNpg@kernel.org>
Date: Thu, 23 Oct 2025 14:09:53 +0800
From: Troy Mitchell <troy.mitchell@...ux.dev>
To: Thomas Gleixner <tglx@...utronix.de>,
	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 08:23:58PM +0200, Thomas Gleixner wrote:
> 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:
Thank you for your reminder again.

                - Troy
>  
> >> # git grep 'This patch' Documentation/process/
> 
> Thanks,
> 
>         tglx