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

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Message-ID: <bb0c95b6-760d-4de1-bc28-8f82e2fc5dd5@arm.com>
Date: Tue, 7 Jan 2025 14:34:38 +0000
From: Vincenzo Frascino <vincenzo.frascino@....com>
To: Jessica Clarke <jrtc27@...c27.com>, Rob Herring <robh@...nel.org>
Cc: 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

Hi Jessica,

Thank you for your review.

On 07/01/2025 12:56, Jessica Clarke wrote:
> 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.
> 

We agree on the concept. It should either be "arm,rainier" or "arm,morello-r0p1"
if we want to capture the information of SMBIOS. When we reach consensus I will
update the patches accordingly (Please have a look at my reply to Rob).

> 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.>

The name morello on its own is too overloaded of meaning if we do not specify to
what we are referring to.

> 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?
> 

I still did not start bringing up to speed the DTS for FVP but I think that we
should distinguish in between SDP and FVP since not everything is the same,
hence it should have something similar to:

	compatible = "arm,morello-fvp", "arm,morello";

> Please CC me on future versions of this series.
> 

Will do.

> Jess

-- 
Regards,
Vincenzo