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

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Message-Id: <20250426-riscv-swab-v4-0-64201404a68c@iencinas.com>
Date: Sat, 26 Apr 2025 16:56:17 +0200
From: Ignacio Encinas <ignacio@...cinas.com>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Alexandre Ghiti <alex@...ti.fr>, 
 Arnd Bergmann <arnd@...db.de>
Cc: Eric Biggers <ebiggers@...nel.org>, 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, Ignacio Encinas <ignacio@...cinas.com>
Subject: [PATCH v4 0/2] Implement endianess swap macros for RISC-V

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.

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,
-- 
Ignacio Encinas <ignacio@...cinas.com>