linux-kernel - Re: [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple AIC driver.

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Date:   Thu, 21 Jan 2021 14:00:19 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Mohamed Mediouni <mohamed.mediouni@...amail.com>
Cc:     Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Hector Martin <marcan@...can.st>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Stan Skowronek <stan@...ellium.com>
Subject: Re: [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple
 AIC driver.

On Thu, Jan 21, 2021 at 1:50 PM Mohamed Mediouni
<mohamed.mediouni@...amail.com> wrote:
> > On 21 Jan 2021, at 13:44, Arnd Bergmann <arnd@...nel.org> wrote:
> >> @@ -186,8 +325,11 @@ static int __init apple_aic_init(struct device_node *node,
> >>       if (WARN(!aic.base, "unable to map aic registers\n"))
> >>               return -EINVAL;
> >>
> >> +       aic.fast_ipi = of_property_read_bool(node, "fast-ipi");
> >
> > Where is this property documented, and what decides which one to use?
> It’s 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