linux-kernel - Re: [PATCH 00/37] arm64: Add initial device trees for Apple M2 Pro/Max/Ultra devices

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Message-ID: <20250904122423.GB89417@robin.jannau.net>
Date: Thu, 4 Sep 2025 14:24:23 +0200
From: Janne Grunau <j@...nau.net>
To: Rob Herring <robh@...nel.org>
Cc: Sven Peter <sven@...nel.org>, Alyssa Rosenzweig <alyssa@...enzweig.io>,
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Subject: Re: [PATCH 00/37] arm64: Add initial device trees for Apple M2
 Pro/Max/Ultra devices

On Tue, Sep 02, 2025 at 02:54:34PM -0500, Rob Herring wrote:
> On Sat, Aug 30, 2025 at 09:16:20AM +0200, Janne Grunau wrote:
> > On Fri, Aug 29, 2025 at 02:51:19PM -0500, Rob Herring wrote:
> > > On Thu, Aug 28, 2025 at 04:01:19PM +0200, Janne Grunau wrote:
> > > > This series adds device trees for Apple's M2 Pro, Max and Ultra based
> > > > devices. The M2 Pro (t6020), M2 Max (t6021) and M2 Ultra (t6022) SoCs
> > > > follow design of the t600x family so copy the structure of SoC *.dtsi
> > > > files.

...

> > > > After discussion with the devicetree maintainers we agreed to not extend
> > > > lists with the generic compatibles anymore [1]. Instead either the first
> > > > compatible SoC or t8103 is used as fallback compatible supported by the
> > > > drivers. t8103 is used as default since most drivers and bindings were
> > > > initially written for M1 based devices.
> > > 
> > > An issue here is any OS without the compatibles added to the drivers 
> > > won't work. Does that matter here? Soon as you need any new drivers or 
> > > significant driver changes it won't. The compatible additions could be 
> > > backported to stable. They aren't really any different than new PCI IDs 
> > > which get backported.
> > 
> > I don't think backporting the driver compatible additions to stable
> > linux is very useful. It is only relevant for t602x devices and the only
> > way to interact with them is the serial console. The T602x PCIe support
> > added in v6.16 requires dart changes (the posted 4th level io page table
> > support) to be useful. After that PCIe ethernet works so there is a
> > practical way to interact with t602x systems. So there are probably zero
> > user of upstream linux on those devices 
> > I'm more concerned about other projects already supporting t602x
> > devices. At least u-boot and OpenBSD will be affected by this. As short
> > term solution m1n1 will add the generic compatibles [1] temporarily.
> > I think keeping this roughly for a year should allow to add the
> > compatibles and wait for "fixed" releases of those projects.
> > I'll send fixes for u-boot once the binding changes are reviewed.
> 
> Honestly, at least in the cases where the generic compatible works for 
> every chip so far, I'd just stick with it. The issue with generic 
> compatibles is more that you don't really know if things are going to be 
> the same or not. And most of the time, the h/w ends up changing.
> 
> If you want to keep it like this since you've already done it, then for 
> all the binding patches:

Let's keep with this series. I still have a branch with dt-binding
changes using the generic compatibles but let's keep this approach to
confusion and duplicate review work.

> Acked-by: Rob Herring (Arm) <robh@...nel.org>

Thanks

Janne