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From:   Anup Patel <anup@brainfault.org>
Date:   Mon, 14 Jun 2021 18:43:25 +0530
Message-ID: <CAAhSdy0jZTqZ+zTazpQLeCnbAHr99t40vEa-_GD0_UjBZsXWzg@mail.gmail.com>
Subject: Re: [RFC PATCH v1 05/10] irqchip: Add ACLINT software interrupt driver
To:     Marc Zyngier <maz@kernel.org>
Cc:     Anup Patel <anup.patel@wdc.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Palmer Dabbelt <palmerdabbelt@google.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Atish Patra <atish.patra@wdc.com>,
        Alistair Francis <Alistair.Francis@wdc.com>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
        DTML <devicetree@vger.kernel.org>
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On Mon, Jun 14, 2021 at 3:08 PM Marc Zyngier <maz@kernel.org> wrote:
>
> On Sun, 13 Jun 2021 13:25:40 +0100,
> Anup Patel <anup@brainfault.org> wrote:
> >
> > On Sun, Jun 13, 2021 at 3:11 PM Marc Zyngier <maz@kernel.org> wrote:
> > >
> > > I'm sorry, but this really isn't an irqchip driver. This is a piece of
> > > arch-specific code that uses *none* of the irq subsystem abstractions
> > > apart from the IRQCHIP_DECLARE() macro.
> >
> > Yes, I was not sure we can call it IRQCHIP hence the RFC PATCH.
> >
> > Both ACLINT MSWI and SSWI are special devices providing only IPI
> > support so I will re-think how to fit this.
>
> It depends on how you think of IPIs in your architecture.
>
> arm64 (and even now 32bit) have been moved to a mode where IPIs are
> normal interrupts, as it helps with other things such as our pseudo
> NMIs, and reduces code duplication. MIPS has done the same for a long
> time (they don't have dedicated HW for that).

RISC-V is also moving in a similar direction with the RISC-V advanced
interrupt architecture (AIA) specification which aims at defining an
interrupt controller having MSI support, virtualization support and
scalable for a large number of CPUs. The RISC-V AIA treats IPIs as
normal interrupts.

The RISC-V ACLINT based IPI support is for RISC-V systems which
only need a simple interrupt controller without MSI support and
virtualization support. These systems will not implement RISC-V AIA.

Regards,
Anup

>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.