linux-kernel - Re: [PATCH] irqchip: riscv-imsic: Add kernel parameter to disable IPIs

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Message-ID: <87wm8tmcsr.ffs@tglx>
Date: Mon, 30 Jun 2025 18:09:24 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Anup Patel <apatel@...tanamicro.com>, Jonathan Corbet <corbet@....net>
Cc: Anup Patel <anup@...infault.org>, Atish Patra <atish.patra@...ux.dev>,
 Palmer Dabbelt <palmer@...belt.com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Alexandre Ghiti <alex@...ti.fr>, Andrew Jones
 <ajones@...tanamicro.com>, linux-doc@...r.kernel.org,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, Anup Patel
 <apatel@...tanamicro.com>
Subject: Re: [PATCH] irqchip: riscv-imsic: Add kernel parameter to disable IPIs

On Wed, Jun 25 2025 at 21:47, Anup Patel wrote:

$Subject...

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

Is it that hard?

> When injecting IPIs to a set of harts, the IMSIC IPI support will
> do a separate MMIO write to SETIPNUM_LE register of each target
> hart. This means on a platform where IMSIC is trap-n-emulated,
> there will be N MMIO traps when injecting IPI to N target harts
> hence IPIs based on IMSIC software injected MSI is slow compared
> to the SBI IPI extension.
>
> Add a kernel parameter to disable IPIs in IMSIC driver for platforms
> with trap-n-emulated IMSIC.

Why do you need a kernel parameter for that. If the platform uses trap-n
emulation, then disable the IPI muck automatically, no?

Thanks,

        tglx