linux-kernel - Re: [PATCH v1 3/6] gpio: realtek-otto: Support per-cpu interrupts

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Date:   Thu, 21 Apr 2022 10:48:26 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Linus Walleij <linus.walleij@...aro.org>,
        Sander Vanheule <sander@...nheule.net>
Cc:     linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        Bartosz Golaszewski <brgl@...ev.pl>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Bert Vermeulen <bert@...t.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 3/6] gpio: realtek-otto: Support per-cpu interrupts

On Thu, 21 Apr 2022 00:04:16 +0100,
Linus Walleij <linus.walleij@...aro.org> wrote:
> 
> On Sat, Apr 9, 2022 at 9:56 PM Sander Vanheule <sander@...nheule.net> wrote:
> 
> > On SoCs with multiple cores, it is possible that the GPIO interrupt
> > controller supports assigning specific pins to one or more cores.
> >
> > IRQ balancing can be performed on a line-by-line basis if the parent
> > interrupt is routed to all available cores, which is the default upon
> > initialisation.
> >
> > Signed-off-by: Sander Vanheule <sander@...nheule.net>
> 
> That sounds complicated.
> 
> Sounds like something the IRQ maintainer (Marc Z) should
> have a quick look at.

This is pretty odd indeed. There seem to be a direct mapping between
the GPIOs and the CPU it interrupts (or at least that's what the code
seem to express). However, I don't see a direct relation between the
CPUs and the chained interrupt. It isn't even clear if this interrupt
itself is per-CPU.

So this begs a few questions:

- is the affinity actually affecting the target CPU? or is it
  affecting the target mux?

- how is the affinity of the mux interrupt actually enforced?

	M.

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