linux-kernel - Re: [PATCH V3 08/10] irqchip: Add LoongArch CPU interrupt controller support

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Date:   Sun, 29 Aug 2021 18:34:21 +0800
From:   Huacai Chen <chenhuacai@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Huacai Chen <chenhuacai@...ngson.cn>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH V3 08/10] irqchip: Add LoongArch CPU interrupt controller support

Hi, Marc,

On Sun, Aug 29, 2021 at 6:10 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On Sun, 29 Aug 2021 10:37:48 +0100,
> Huacai Chen <chenhuacai@...il.com> wrote:
>
> > > Are you saying that there is no way for the interrupt controller
> > > driver to figure out the hwirq number on its own?  That would seem
> > > pretty odd (even the MIPS GIC has that). Worse case, you can provide
> > > an arch-specific helper that exposes the current hwirq based on the
> > > vector that triggered.
> > We can get the hwirq number by reading CSR.ESTAT register, but in this
> > way "vectored interrupts" is meaningless.
>
> Let's face it, the way you use vectored interrupts makes zero sense
> already. The whole point of vectored interrupts is that the CPU can
> branch to the handler directly, making the interrupt handling cheaper
> as there should be no additional decoding and you can run the final
> handler immediately. Here, all your interrupts point to the same
> "default handler"...
The default handler can be overridden by arch code.

Huacai
>
> What do vectored interrupts bring? "Absolutely Nothing! (say it again!)"
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.