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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Thu, 21 Jan 2021 14:00:19 +0100
Message-ID: <CAK8P3a3g888Rn=FRaYB80d5ehHA8b9GUZfa0J+D1nXPKkzcpig@mail.gmail.com>
Subject: Re: [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple
 AIC driver.
To:     Mohamed Mediouni <mohamed.mediouni@caramail.com>
Cc:     Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Hector Martin <marcan@marcan.st>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
        Stan Skowronek <stan@corellium.com>
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On Thu, Jan 21, 2021 at 1:50 PM Mohamed Mediouni
<mohamed.mediouni@caramail.com> wrote:
> > On 21 Jan 2021, at 13:44, Arnd Bergmann <arnd@kernel.org> wrote:
> >> @@ -186,8 +325,11 @@ static int __init apple_aic_init(struct device_no=
de *node,
> >>       if (WARN(!aic.base, "unable to map aic registers\n"))
> >>               return -EINVAL;
> >>
> >> +       aic.fast_ipi =3D of_property_read_bool(node, "fast-ipi");
> >
> > Where is this property documented, and what decides which one to use?
> It=E2=80=99s getting documented in the next patch set.
>
> This property is there to enable support for older iPhone processors
> later on, some of which do not have fast IPI support.
>
> On Apple M1, fast-ipi is always on.

Ok, makes sense. Does fast-ipi mean you cannot use the other mode at
all, or is it just faster as implied by the name? If so, how much faster?

       Arnd