Re: [PATCH v2 1/2] include/uapi/linux/swab.h: move default implementation for swab macros into asm-generic

From: Ignacio Encinas Rubio <ignacio@iencinas.com>
To: Arnd Bergmann <arnd@arndb.de>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Alexandre Ghiti <alex@ghiti.fr>
Cc: "Eric Biggers" <ebiggers@kernel.org>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-kernel-mentees@lists.linux.dev,
	"Shuah Khan" <skhan@linuxfoundation.org>,
	"Zhihang Shao" <zhihang.shao.iscas@gmail.com>,
	"Björn Töpel" <bjorn@kernel.org>,
	Linux-Arch <linux-arch@vger.kernel.org>
Subject: Re: [PATCH v2 1/2] include/uapi/linux/swab.h: move default implementation for swab macros into asm-generic
Date: Wed, 19 Mar 2025 22:37:36 +0100	[thread overview]
Message-ID: <4d45df0c-d44e-4bb6-8daa-0dba1b834bc4@iencinas.com> (raw)
In-Reply-To: <2afab9dc-e39c-4399-ac5a-87ade4da5ab0@app.fastmail.com>

On 19/3/25 22:12, Arnd Bergmann wrote:
> On Wed, Mar 19, 2025, at 22:09, Ignacio Encinas wrote:
>> Move the default byteswap implementation into asm-generic so that it can
>> be included from arch code.
>>
>> This is required by RISC-V in order to have a fallback implementation
>> without duplicating it.
>>
>> Signed-off-by: Ignacio Encinas <ignacio@iencinas.com>
>> ---
>>  include/uapi/asm-generic/swab.h | 32 ++++++++++++++++++++++++++++++++
>>  include/uapi/linux/swab.h       | 33 +--------------------------------
>>  2 files changed, 33 insertions(+), 32 deletions(-)
>>
> 
> I think we should just remove these entirely in favor of the
> compiler-povided built-ins.

Got it. I assumed they existed to explicitly avoid relying on
__builtin_bswap as they might not exist. However, I did a quick grep and
found that there are some uses in the wild.

I couldn't find compiler builtins for ___constant_swahb32 nor 
___constant_swahw32, so I guess I'll leave them as they are.

Thank you!