linux-kernel - Re: [PATCH v7 2/4] arm64: Add BBM Level 2 cpu feature

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Message-ID: <aFQUmWC1MYhai1fo@arm.com>
Date: Thu, 19 Jun 2025 14:46:01 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Mikołaj Lenczewski <miko.lenczewski@....com>
Cc: ryan.roberts@....com, yang@...amperecomputing.com, will@...nel.org,
	jean-philippe@...aro.org, robin.murphy@....com, joro@...tes.org,
	maz@...nel.org, oliver.upton@...ux.dev, joey.gouly@....com,
	james.morse@....com, broonie@...nel.org, ardb@...nel.org,
	baohua@...nel.org, suzuki.poulose@....com, david@...hat.com,
	jgg@...pe.ca, nicolinc@...dia.com, jsnitsel@...hat.com,
	mshavit@...gle.com, kevin.tian@...el.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev
Subject: Re: [PATCH v7 2/4] arm64: Add BBM Level 2 cpu feature

On Thu, Jun 19, 2025 at 12:51:32PM +0100, Mikołaj Lenczewski wrote:
> On Thu, Jun 19, 2025 at 12:05:05PM +0100, Catalin Marinas wrote:
> > On Tue, Jun 17, 2025 at 09:51:02AM +0000, Mikołaj Lenczewski wrote:
> > > +	 * whether the MIDR check passes. This is because we specifically
> > > +	 * care only about a stricter form of BBML2 (one guaranteeing noabort),
> > > +	 * and so the MMFR2 check is pointless (all implementations passing the
> > > +	 * MIDR check should also pass the MMFR2 check).
> > 
> > I think there's at least one implementation that behaves as
> > BBML2-noabort but does not have the ID field advertising BBML2.
> > 
> 
> Yes, I put "should" instead of "will" because of the AmpereOne
> situation, but I didn't want to "name and shame". Should I explicitly
> call this out? Or would you like me to soften the vocabulary here to imply
> that as long as the MIDR passes, the MMFR2 check is not important?

I missed the "should" part. Anyway, I would just drop the explanation
from "This is because...".

-- 
Catalin