linux-kernel - Re: [PATCH v4 2/4] arm64: dts: morello: Add support for common functionalities

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Message-ID: <Z30kbmA-3h-Rhg7l@Jessicas-MacBook-Pro>
Date: Tue, 7 Jan 2025 12:56:14 +0000
From: Jessica Clarke <jrtc27@...c27.com>
To: Rob Herring <robh@...nel.org>
Cc: Vincenzo Frascino <vincenzo.frascino@....com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Liviu Dudau <liviu.dudau@....com>,
	Sudeep Holla <sudeep.holla@....com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Russell King <linux@...linux.org.uk>
Subject: Re: [PATCH v4 2/4] arm64: dts: morello: Add support for common
 functionalities

On Fri, Jan 03, 2025 at 04:14:31PM -0600, Rob Herring wrote:
> On Fri, Jan 3, 2025 at 12:16 PM Vincenzo Frascino
> <vincenzo.frascino@....com> wrote:
> > +       cpus {
> > +               #address-cells = <2>;
> > +               #size-cells = <0>;
> > +
> > +               cpu0: cpu@0 {
> > +                       compatible = "arm,neoverse-n1";
> 
> I'm pretty sure the N1 doesn't support CHERI/morello. Perhaps
> "arm,neoverse-n1-morello" if we want to capture what it is derived
> from and since "arm,morello" is taken already.

Rainier is the codename of the core itself, and Morello LLVM recognises
-mcpu=rainier not -mcpu=morello (there's -march=morello instead), so
perhaps it should really be "arm,rainier". Though SMBIOS reports it as
Morello-R0P1 so it may be best to use "arm,morello" here.

The real problem is that the board compatible has changed to include a
generic "arm,morello" node, with the argument that a v2 board could
appear. So why not instead change *that* to be something like:

  compatible = "arm,morello-sdp-v1", "arm,morello-sdp";

Then you can use "arm,morello" here for the cores.

Though some of this may depend on what the FVP's DTS looks like; is it
going to claim to be a Morello SDP, or does there need to be a common
denominator compatible beneath that it can use?

Please CC me on future versions of this series.

Jess