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From: Rob Herring <robh@kernel.org>
To: Mohamed Mediouni <mohamed.mediouni@caramail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Arnd Bergmann <arnd@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Hector Martin <marcan@marcan.st>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Stan Skowronek <stan@corellium.com>
Subject: Re: [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple AIC driver.
Date: Thu, 21 Jan 2021 11:37:46 -0600
Message-ID: <CAL_Jsq+V74tMGJ==OVdsssfqTTa3TrFujfRjj0174uZNonpQSA@mail.gmail.com> (raw)
In-Reply-To: <FEDB12D6-2916-4430-A8DC-FBD9352F3730@caramail.com>

On Thu, Jan 21, 2021 at 10:43 AM Mohamed Mediouni
<mohamed.mediouni@caramail.com> wrote:
> > On 21 Jan 2021, at 17:40, Rob Herring <robh@kernel.org> wrote:
> > On Thu, Jan 21, 2021 at 6:52 AM Mohamed Mediouni
> > <mohamed.mediouni@caramail.com> wrote:
> >>> On 21 Jan 2021, at 13:44, Arnd Bergmann <arnd@kernel.org> wrote:
> >>> On Wed, Jan 20, 2021 at 2:27 PM Mohamed Mediouni
> >>> <mohamed.mediouni@caramail.com> 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.
> >
> > This should be implied by the compatible string which needs to be more
> > specific and include the SoC name.
> >
> > Rob
>
> Then we’ll eventually have two aic compatible strings, aic which is compatible
> with Apple A7 onwards and aicv2 which is a superset with fast IPI (introduced
> on the Apple A11, 3 years ago, with no further programmer-visible changes since
> then).
>
> Does that look right?

If we did this from the start, it would evolve like this:

A7: "AAPL,a7-aic"
A8: "AAPL,a8-aic", "AAPL,a7-aic"  # Read this as A8 AIC is backwards
compatible with A7 AIC
A9: "AAPL,a9-aic", "AAPL,a7-aic"

A11: "AAPL,a11-aic", "AAPL,a7-aic"

If the A11 version could work on an OS that only supported the
original model (sounds like this is the case) Or if it's not backwards
compatible:

A11: "AAPL,a11-aic"

If the A11 is different and not backwards compatible.

Then M1 could be:

M1: "AAPL,m1-aic", "AAPL,a11-aic"

Or to even support an OS with only v1 support:

M1: "AAPL,m1-aic", "AAPL,a11-aic", "AAPL,a7-aic"

You don't really need the fallback here because there isn't any
existing OS support and the baseline is the M1.

If you want to have generic fallback compatible strings with versions,
that's fine too. I'm not really a fan of version numbers that are just
made up by the binding author though. Most SoC vendors don't have
rigorous versioning of their IP and those that do seem to have a new
version on every SoC.

The important part is *always* having an SoC specific compatible so
you can deal with any quirk or feature without having to change the
DTB. Everyone says blocks are 'the same' until they aren't.

Rob

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Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-20 13:27 [RFC PATCH 0/7] Linux on Apple Silicon Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 1/7] arm64: kernel: FIQ support Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 2/7] arm64: kernel: Add a WFI hook Mohamed Mediouni
2021-01-20 16:46   ` Alexander Graf
     [not found]     ` <94C20F55-D3B8-4349-B26F-9EA8AAEBF639@caramail.com>
2021-01-21 12:33       ` Hector Martin 'marcan'
2021-01-21 10:52   ` Arnd Bergmann
2021-01-21 11:01     ` Mohamed Mediouni
2021-01-21 11:36       ` Arnd Bergmann
2021-01-20 13:27 ` [RFC PATCH 3/7] arm64: mm: use nGnRnE instead of nGnRE on Apple processors Mohamed Mediouni
2021-01-20 16:47   ` Alexander Graf
2021-01-20 18:06     ` Mohamed Mediouni
2021-01-20 18:10       ` Alexander Graf
2021-01-21 11:27   ` Will Deacon
2021-01-21 11:38     ` Arnd Bergmann
2021-01-21 11:44     ` Marc Zyngier
2021-01-21 12:47       ` Will Deacon
2021-01-21 15:12         ` Mohamed Mediouni
2021-01-21 16:25           ` Marc Zyngier
2021-01-21 17:55             ` Will Deacon
2021-01-21 18:15               ` Marc Zyngier
2021-01-21 18:22                 ` Mohamed Mediouni
2021-01-21 18:22                 ` Will Deacon
2021-01-20 13:27 ` [RFC PATCH 4/7] irqchip/apple-aic: Add support for Apple AIC Mohamed Mediouni
2021-01-20 17:11   ` Alexander Graf
2021-01-20 18:04     ` Mohamed Mediouni
2021-01-20 20:16       ` Andrew Lunn
2021-01-20 21:18   ` Stan Skowronek
2021-01-21  9:48   ` Linus Walleij
2021-01-21 10:37     ` Arnd Bergmann
2021-01-21 15:29       ` Hector Martin 'marcan'
2021-01-21 17:09         ` Rob Herring
2021-01-21 17:45       ` Rob Herring
2021-01-21 16:44     ` Rob Herring
2021-01-21 16:53   ` Hector Martin 'marcan'
2021-01-20 13:27 ` [RFC PATCH 5/7] arm64/Kconfig: Add Apple Silicon SoC platform Mohamed Mediouni
2021-01-20 13:27 ` [RFC PATCH 6/7] arm64: kernel: Apple CPU start driver Mohamed Mediouni
2021-01-21 11:14   ` Arnd Bergmann
2021-01-20 13:27 ` [RFC PATCH 7/7] irqchip/apple-aic: add SMP support to the Apple AIC driver Mohamed Mediouni
2021-01-21 12:44   ` Arnd Bergmann
2021-01-21 12:50     ` Mohamed Mediouni
2021-01-21 13:00       ` Arnd Bergmann
2021-01-21 13:01         ` Hector Martin 'marcan'
2021-01-21 13:22       ` Marc Zyngier
2021-01-21 13:32         ` Mark Rutland
2021-01-21 14:05           ` Marc Zyngier
2021-01-21 13:34         ` Mohamed Mediouni
2021-01-21 14:10           ` Marc Zyngier
2021-01-21 15:09             ` Arnd Bergmann
2021-01-21 15:18               ` Mohamed Mediouni
2021-01-21 16:40       ` Rob Herring
2021-01-21 16:43         ` Mohamed Mediouni
2021-01-21 17:37           ` Rob Herring [this message]
2021-01-21 18:08             ` Mohamed Mediouni
2021-01-21 18:57               ` Rob Herring
2021-02-02 19:15   ` Linus Walleij

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