linux-kernel - Re: [PATCH v2 2/2] riscv: introduce asm/swab.h

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Message-ID: <20250321033718.GA98513@sol.localdomain>
Date: Thu, 20 Mar 2025 20:37:18 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Ignacio Encinas <ignacio@...cinas.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Alexandre Ghiti <alex@...ti.fr>, Arnd Bergmann <arnd@...db.de>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev, skhan@...uxfoundation.org,
	Zhihang Shao <zhihang.shao.iscas@...il.com>,
	Björn Töpel <bjorn@...nel.org>,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH v2 2/2] riscv: introduce asm/swab.h

On Wed, Mar 19, 2025 at 10:09:46PM +0100, Ignacio Encinas wrote:
> +#define ARCH_SWAB(size) \
> +static __always_inline unsigned long __arch_swab##size(__u##size value) \
> +{									\
> +	unsigned long x = value;					\
> +									\
> +	asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0,			\
> +			     RISCV_ISA_EXT_ZBB, 1)			\
> +			     :::: legacy);				\

Is there a reason to use this instead of
riscv_has_extension_likely(RISCV_ISA_EXT_ZBB) which seems to do the same thing,
including using a static branch?

- Eric