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 13:32:35 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Mohamed Mediouni <mohamed.mediouni@...amail.com>,
        Arnd Bergmann <arnd@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Hector Martin <marcan@...can.st>, linux-kernel@...r.kernel.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 01:22:37PM +0000, Marc Zyngier wrote:
> On 2021-01-21 12:50, Mohamed Mediouni wrote:
> > > On 21 Jan 2021, at 13:44, Arnd Bergmann <arnd@...nel.org> wrote:
> > > 
> > > On Wed, Jan 20, 2021 at 2:27 PM Mohamed Mediouni
> 
> [...]
> 
> > > > +       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.
> 
> Then please focus on a single implementation. Additional features can
> always be merged later once something is up and running.
> 
> Also, there sysregs can be detected by matching the MIDR, so I don't
> think we need a DT property for that.

Generally we do not detect IMP-DEF sysregs based on MIDR because they
won't necessarily be exposed to a VM, so I suspect that we do need DT
properties to describe that IMP-DEF sysregs are accessible, and should
not rely on the MIDR alone. Maybe that's implicit in another property,
but worth bearing in mind.

Thanks,
Mark.