linux-kernel - Re: [PATCH v3 cmpxchg 4/4] ARM: Emulate one-byte cmpxchg

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Message-ID: <CACRpkdaYQWGsjtDPzbJS4C9Y9z8JGv=3ihQrVKvegJf8ujqSmA@mail.gmail.com>
Date: Tue, 4 Jun 2024 22:52:23 +0200
From: Linus Walleij <linus.walleij@...aro.org>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org, 
	kernel-team@...a.com, elver@...gle.com, akpm@...ux-foundation.org, 
	tglx@...utronix.de, peterz@...radead.org, dianders@...omium.org, 
	pmladek@...e.com, torvalds@...ux-foundation.org, arnd@...db.de, 
	Mark Brown <broonie@...nel.org>, Naresh Kamboju <naresh.kamboju@...aro.org>, 
	Nathan Chancellor <nathan@...nel.org>, "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>, 
	Andrew Davis <afd@...com>, Eric DeVolder <eric.devolder@...cle.com>, Rob Herring <robh@...nel.org>, 
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 cmpxchg 4/4] ARM: Emulate one-byte cmpxchg

Hi Paul,

thanks for your patch! This caught my eye:

On Tue, Jun 4, 2024 at 7:04 PM Paul E. McKenney <paulmck@...nel.org> wrote:

> Use the new cmpxchg_emu_u8() to emulate one-byte cmpxchg() on ARM systems
> with ARCH < ARMv6K.

ARCH == ARMv6.

This ARCH < ARMv6K comes from inversion of the the a bit terse
comment for ifndef CONFIG_CPU_V6, which means "out of the
post-v6 CPUs, the following applies to those > V6".

The code in the patch, IIUC make use of cmpxchg_emu_u8()
if and only if the CPU is V6.

> -#ifndef CONFIG_CPU_V6  /* min ARCH >= ARMv6K */
> +#ifdef CONFIG_CPU_V6   /* min ARCH < ARMv6K */

This is now a set with one member so this comment should say:

/* ARCH == ARMv6 */

After this change.

Yours,
Linus Walleij