linux-kernel - [PATCH v2 0/5] riscv: Use __riscv_has_extension

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Message-Id: <20250821-riscv-altn-helper-wip-v2-0-9586fa702f78@iscas.ac.cn>
Date: Thu, 21 Aug 2025 17:16:30 +0800
From: Vivian Wang <wangruikang@...as.ac.cn>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Alexandre Ghiti <alex@...ti.fr>, Yury Norov <yury.norov@...il.com>, 
 Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Charlie Jenkins <charlie@...osinc.com>, 
 Xiao Wang <xiao.w.wang@...el.com>, 
 Christoph Müllner <christoph.muellner@...ll.eu>, 
 Vivian Wang <wangruikang@...as.ac.cn>, Vivian Wang <uwu@...m.page>, 
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 0/5] riscv: Use __riscv_has_extension_{likely,unlikely}

There are about a dozen uses of asm goto in arch/riscv just to select
between two code paths with the alternative mechanism. Convert them to
the existing helpers __riscv_has_extension_{likely,unlikely}.

In each case, I have preserved the existing code's choice of asm goto
pattern while picking between "likely" and "unlikely", namely:

  ALTERNATIVE("j %l[no]", "nop", ...)   -> "likely"
  ALTERNATIVE("nop", "j %l[yes]", ...)  -> "unlikely"

Since the helpers are just implementations of these patterns, the
performance should be the same as before.

These patches are also available at:

https://github.com/dramforever/linux/tree/riscv/altn-helper/v2

---
Changes in v2:
- Cc'd authors who initially introduced the asm goto blocks
- Use existing __riscv_has_extension_{likely,unlikely} instead
- Remove bogus comment for Zbb being likely (checksum)
- Restructured patch to minimize diff (bitops, hweight, cmpxchg)
- Link to v1: https://lore.kernel.org/r/20250820-riscv-altn-helper-wip-v1-0-c3c626c1f7e6@iscas.ac.cn

---
Vivian Wang (5):
      riscv: pgtable: Use __riscv_has_extension_unlikely
      riscv: checksum: Use __riscv_has_extension_likely
      riscv: hweight: Use __riscv_has_extension_likely
      riscv: bitops: Use __riscv_has_extension_likely
      riscv: cmpxchg: Use __riscv_has_extension_likely

 arch/riscv/include/asm/arch_hweight.h | 24 ++++++----------
 arch/riscv/include/asm/bitops.h       | 32 ++++++---------------
 arch/riscv/include/asm/checksum.h     | 13 +++------
 arch/riscv/include/asm/cmpxchg.h      | 12 +++-----
 arch/riscv/include/asm/pgtable.h      | 15 +++++-----
 arch/riscv/lib/csum.c                 | 53 ++++++++---------------------------
 arch/riscv/mm/pgtable.c               | 22 +++++++--------
 7 files changed, 53 insertions(+), 118 deletions(-)
---
base-commit: 062b3e4a1f880f104a8d4b90b767788786aa7b78
change-id: 20250820-riscv-altn-helper-wip-00af3a552c37

Best regards,
-- 
Vivian "dramforever" Wang