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From: "Arnd Bergmann" <arnd@arndb.de>
To: "Ignacio Encinas" <ignacio@iencinas.com>,
	"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: Fri, 21 Mar 2025 11:23:18 +0100	[thread overview]
Message-ID: <583340a9-411d-406f-aee9-d3e2eb80ca43@app.fastmail.com> (raw)
In-Reply-To: <ac0b1f3e-6abe-4de2-bf5a-a4b3207a22c3@iencinas.com>

On Thu, Mar 20, 2025, at 23:36, Ignacio Encinas Rubio wrote:
> On 19/3/25 22:49, Arnd Bergmann wrote:
>> On Wed, Mar 19, 2025, at 22:37, Ignacio Encinas Rubio wrote:
>>> On 19/3/25 22:12, Arnd Bergmann wrote:
>> Right, I do remember when we had a discussion about this maybe
>> 15 years ago when gcc didn't have the builtins on all architectures
>> yet, but those versions are long gone, and we never cleaned it up.
>
> I just had a chance to look at this and it looks a bit more complex than
> I initially thought. ___constant_swab macros are used in more places
> than I expected, and {little,big}_endian.h define their own macros that
> are used elsewhere, ...
>
> It is not clear to me how to proceed here. I could:
>
>   1) Just remove ___constant_swab macros and replace them with
>   __builtin_swap everywhere
>
>   2) Go a step further and evaluate removing __constant_htonl and
>   relatives
>
> Let me know what you think is the best option :)

I think we can start enabling CONFIG_ARCH_USE_BUILTIN_BSWAP
on all architectures and removing the custom versions
from arch/*/include/uapi/asm/swab.h, which all seem to
predate the compiler builtins and likely produce worse code.

    Arnd

WARNING: multiple messages have this Message-ID (diff)
From: "Arnd Bergmann" <arnd@arndb.de>
To: "Ignacio Encinas" <ignacio@iencinas.com>,
	"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: Fri, 21 Mar 2025 11:23:18 +0100	[thread overview]
Message-ID: <583340a9-411d-406f-aee9-d3e2eb80ca43@app.fastmail.com> (raw)
In-Reply-To: <ac0b1f3e-6abe-4de2-bf5a-a4b3207a22c3@iencinas.com>

On Thu, Mar 20, 2025, at 23:36, Ignacio Encinas Rubio wrote:
> On 19/3/25 22:49, Arnd Bergmann wrote:
>> On Wed, Mar 19, 2025, at 22:37, Ignacio Encinas Rubio wrote:
>>> On 19/3/25 22:12, Arnd Bergmann wrote:
>> Right, I do remember when we had a discussion about this maybe
>> 15 years ago when gcc didn't have the builtins on all architectures
>> yet, but those versions are long gone, and we never cleaned it up.
>
> I just had a chance to look at this and it looks a bit more complex than
> I initially thought. ___constant_swab macros are used in more places
> than I expected, and {little,big}_endian.h define their own macros that
> are used elsewhere, ...
>
> It is not clear to me how to proceed here. I could:
>
>   1) Just remove ___constant_swab macros and replace them with
>   __builtin_swap everywhere
>
>   2) Go a step further and evaluate removing __constant_htonl and
>   relatives
>
> Let me know what you think is the best option :)

I think we can start enabling CONFIG_ARCH_USE_BUILTIN_BSWAP
on all architectures and removing the custom versions
from arch/*/include/uapi/asm/swab.h, which all seem to
predate the compiler builtins and likely produce worse code.

    Arnd

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linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  reply	other threads:[~2025-03-21 10:23 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-03-19 21:09 [PATCH v2 0/2] Implement endianness swap macros for RISC-V Ignacio Encinas
2025-03-19 21:09 ` Ignacio Encinas
2025-03-19 21:09 ` [PATCH v2 1/2] include/uapi/linux/swab.h: move default implementation for swab macros into asm-generic Ignacio Encinas
2025-03-19 21:09   ` Ignacio Encinas
2025-03-19 21:12   ` Arnd Bergmann
2025-03-19 21:12     ` Arnd Bergmann
2025-03-19 21:37     ` Ignacio Encinas Rubio
2025-03-19 21:37       ` Ignacio Encinas Rubio
2025-03-19 21:49       ` Arnd Bergmann
2025-03-19 21:49         ` Arnd Bergmann
2025-03-20 22:36         ` Ignacio Encinas Rubio
2025-03-20 22:36           ` Ignacio Encinas Rubio
2025-03-21 10:23           ` Arnd Bergmann [this message]
2025-03-21 10:23             ` Arnd Bergmann
2025-03-21 18:38             ` Ignacio Encinas Rubio
2025-03-21 18:38               ` Ignacio Encinas Rubio
2025-03-19 21:09 ` [PATCH v2 2/2] riscv: introduce asm/swab.h Ignacio Encinas
2025-03-19 21:09   ` Ignacio Encinas
2025-03-21  3:37   ` Eric Biggers
2025-03-21  3:37     ` Eric Biggers
2025-03-21 21:07     ` Ignacio Encinas Rubio
2025-03-21 21:07       ` Ignacio Encinas Rubio

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