Re: [PATCH v2 02/25] dt-bindings: arm: apple: Add bindings for Apple ARM platforms

From: Hector Martin <marcan@marcan.st>
To: Krzysztof Kozlowski <krzk@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Arnd Bergmann <arnd@kernel.org>, Rob Herring <robh@kernel.org>,
	Tony Lindgren <tony@atomide.com>, Marc Zyngier <maz@kernel.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
	Alexander Graf <graf@amazon.com>, Olof Johansson <olof@lixom.net>,
	Mohamed Mediouni <mohamed.mediouni@caramail.com>,
	Stan Skowronek <stan@corellium.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	Mark Kettenis <mark.kettenis@xs4all.nl>
Subject: Re: [PATCH v2 02/25] dt-bindings: arm: apple: Add bindings for Apple ARM platforms
Date: Tue, 16 Feb 2021 23:30:08 +0900	[thread overview]
Message-ID: <9729c3c2-787e-2894-ddfb-fc9c07d74086@marcan.st> (raw)
In-Reply-To: <20210215174803.5oalkkmotpc7d7vm@kozik-lap>

On 16/02/2021 02.48, Krzysztof Kozlowski wrote:
> On Mon, Feb 15, 2021 at 09:16:50PM +0900, Hector Martin wrote:
>> +description: |
>> +  Apple ARM ("Apple Silicon") platforms should contain compatible strings
>> +  in the following format:
>> +
>> +  - apple,j274 (board/device ID)
>> +  - apple,m1 (SoC name)
>> +  - apple,arm-platform (Apple Silicon)
> 
> This description is irrelevant because the rules come from schema below.
> Maybe instead write few words about the platform? Or describe how to get
> the board/device ID if it is not obvious?

Good point. Actually, I've gone back and forth over this a few times,
but I'm going to change the SoC name. Apple calls these things by 5
different names, but the only two that make any sense to consider are
the marketing name ("m1") and the SoC name ("t8103"). I'm going to
switch to the latter (so `apple,t8103`).

In the past, Apple have dual-sourced SoCs with different IDs under the
same marketing name, and Apple themselves name most of their compatible
properties after the lowest-compatible SoC name, so I'm going to go with
that after all. This will save us grief in the future if they do that
again, and I think I get to pick the color of this bike shed :)

Given that, I expanded a bit on the description. Let me know what you think:

description: |
   ARM platforms using SoCs designed by Apple Inc., branded "Apple Silicon".

   This currently includes devices based on the "M1" SoC, starting with the
   three Mac models released in late 2020:

   - Mac mini (M1, 2020)
   - MacBook Pro (13-inch, M1, 2020)
   - MacBook Air (M1, 2020)

   The compatible property should follow this format:

   compatible = "apple,<targettype>", "apple,<socid>", "apple,arm-platform";

   <targettype> represents the board/device and comes from the `target-type`
   property of the root node of the Apple Device Tree, lowercased. It can be
   queried on macOS using the following command:

   $ ioreg -d2 -l | grep target-type

   <socid> is the lowercased SoC ID. Apple uses at least *five* different
   names for their SoCs:

   - Marketing name ("M1")
   - Internal name ("H13G")
   - Codename ("Tonga")
   - SoC ID ("T8103")
   - Package/IC part number ("APL1102")

   Devicetrees should use the the lowercased SoC ID, to avoid confusion if
   multiple SoCs share the same marketing name. This can be obtained from
   the `compatible` property of the arm-io node of the Apple Device Tree,
   which can be queried as follows on macOS:

   $ ioreg -n arm-io | grep compatible

-- 
Hector Martin (marcan@marcan.st)
Public Key: https://mrcn.st/pub

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