linux-kernel - Re: [PATCH v2 14/25] dt-bindings: interrupt-controller: Add DT bindings for apple-aic

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Date:   Tue, 16 Feb 2021 12:00:32 +0100 (CET)
From:   Mark Kettenis <mark.kettenis@...all.nl>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     marcan@...can.st, linux-arm-kernel@...ts.infradead.org,
        maz@...nel.org, robh@...nel.org, olof@...om.net, krzk@...nel.org,
        tony@...mide.com, mohamed.mediouni@...amail.com,
        stan@...ellium.com, graf@...zon.com, will@...nel.org,
        linus.walleij@...aro.org, mark.rutland@....com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 14/25] dt-bindings: interrupt-controller: Add DT
 bindings for apple-aic

> From: Arnd Bergmann <arnd@...nel.org>
> Date: Tue, 16 Feb 2021 10:41:11 +0100
> 
> On Mon, Feb 15, 2021 at 1:17 PM Hector Martin <marcan@...can.st> wrote:
> > +
> > +      The 2nd cell contains the interrupt number.
> > +        - HW IRQs: interrupt number
> > +        - FIQs:
> > +          - 0: physical HV timer
> > +          - 1: virtual HV timer
> > +          - 2: physical guest timer
> > +          - 3: virtual guest timer
> 
> I wonder if you could just model the FIQ as a single shared level interrupt
> (which is essentially what it is), and have every driver that uses it do a
> request_irq() on the same IRQ number.
> 
> This would avoid having to come up with a fake binding for it, and simplify
> the implementation that then no longer has to peek into each interrupt
> source.

That would tie the binding more closely to the implementation as it
would remove the option of peeking at the interrupt source.  And
wouldn't it mean that the arch_timer driver would need to know whether
the interrupt is shared or not?