linux-kernel - Re: [PATCH v4 0/2] Implement endianess swap macros for RISC-V

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Message-ID: <mhng-3695679f-b501-42f4-95e0-69457773b787@palmer-ri-x1c9a>
Date: Thu, 08 May 2025 10:32:14 -0700 (PDT)
From: Palmer Dabbelt <palmer@...belt.com>
To: ignacio@...cinas.com, Arnd Bergmann <arnd@...db.de>
CC: Paul Walmsley <paul.walmsley@...ive.com>, alex@...ti.fr, ebiggers@...nel.org,
  linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linux.dev,
  skhan@...uxfoundation.org, zhihang.shao.iscas@...il.com, bjorn@...nel.org, linux-arch@...r.kernel.org,
  ignacio@...cinas.com
Subject:     Re: [PATCH v4 0/2] Implement endianess swap macros for RISC-V

On Sat, 26 Apr 2025 07:56:17 PDT (-0700), ignacio@...cinas.com wrote:
> Motivated by [1]. A couple of things to note:
>
> RISC-V needs a default implementation to fall back on. There is one
> available in include/uapi/linux/swab.h but that header can't be included
> from arch/riscv/include/asm/swab.h. Therefore, the first patch in this
> series moves the default implementation into asm-generic.

This seems fine to me, so 

Acked-by: Palmer Dabbelt <palmer@...osinc.com>

It's asm-generic, though, so I usually try to wait for a review from 
Arnd for those.

> Tested with crc_kunit as pointed out here [2]. I can't provide
> performance numbers as I don't have RISC-V hardware yet.
>
> [1] https://lore.kernel.org/all/20250302220426.GC2079@quark.localdomain/
> [2] https://lore.kernel.org/all/20250216225530.306980-1-ebiggers@kernel.org/
>
> Signed-off-by: Ignacio Encinas <ignacio@...cinas.com>
> ---
> Changes in v4:
>
> - Add missing include in the 1st patch, reported by
>   https://lore.kernel.org/all/202504042300.it9RcOSt-lkp@intel.com/
> - Rewrite the ARCH_SWAB macro as suggested by Arnd
> - Define __arch_swab64 for CONFIG_32BIT (Ben)
> - Link to v3: https://lore.kernel.org/r/20250403-riscv-swab-v3-0-3bf705d80e33@iencinas.com
>
> Arnd, I know you don't like Patch 1 but I tried your suggestions and
> couldn't make them work. Please let me know if I missed anything [3] [4]
>
> [3] https://lore.kernel.org/linux-riscv/f5464e26-faa0-48f1-8585-9ce52c8c9f5f@iencinas.com/
> [4] https://lore.kernel.org/linux-riscv/b3b59747-0484-4042-bdc4-c067688e3bfe@iencinas.com/
>
> Changes in v3:
>
> PATCH 2:
>   Use if(riscv_has_extension_likely) instead of asm goto (Eric). It
>   looks like both versions generate the same assembly. Perhaps we should
>   do the same change in other places such as arch/riscv/include/asm/bitops.h
> - Link to v2: https://lore.kernel.org/r/20250319-riscv-swab-v2-0-d53b6d6ab915@iencinas.com
>
> Changes in v2:
> - Introduce first patch factoring out the default implementation into
>   asm-generic
> - Remove blank line to make checkpatch happy
> - Link to v1: https://lore.kernel.org/r/20250310-riscv-swab-v1-1-34652ef1ee96@iencinas.com
>
> ---
> Ignacio Encinas (2):
>       include/uapi/linux/swab.h: move default implementation for swab macros into asm-generic
>       riscv: introduce asm/swab.h
>
>  arch/riscv/include/asm/swab.h   | 62 +++++++++++++++++++++++++++++++++++++++++
>  include/uapi/asm-generic/swab.h | 33 ++++++++++++++++++++++
>  include/uapi/linux/swab.h       | 33 +---------------------
>  3 files changed, 96 insertions(+), 32 deletions(-)
> ---
> base-commit: a7f2e10ecd8f18b83951b0bab47ddaf48f93bf47
> change-id: 20250307-riscv-swab-b81b94a9ac1b
>
> Best regards,