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arm64: fpsimd: Use assembler for baseline SME instructions

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We currently support assemblers which do not support SME instructions,
and have macros to manually encode SME instructions. This was
necessary historically as SME support was developed before assembler
support was widely available, but things have changed:

* All currently supported versions of LLVM support baseline SME
  instructions. Building the kernel requires LLVM 15+, while LLVM 13+
  supports SME.

* GNU binutils has supported baseline SME instructions since 2.38, which
  was released on 09 February 2022. Toolchains using this or later are
  widely available. For example Debian 12 (released on 10 June 2023)
  provides binutils 2.40. Toolchains provided kernel.org provide
  binutils 2.38+ since the GCC 12.1.0 release (released between 06 May
  2022 and 17 August 2022).

* For various reasons, SME support was marked as BROKEN, and re-enabled
  in v6.16 (released on 27 July 2025). The earliest support LTS kernel
  with SME support is v6.18.y, v6.18 was tagged on 30 November 2025, and
  contemporary toolchains (GCC 15.2 and binutils 2.45) supported
  baseline SME instructions.

* Any distribution which intends to support SME will presumably have a
  toolchain that supports baseline SME instructions such that userspace
  can be built.

Considering the above, there's no practical benefit to allowing SME to
be built when the toolchain doesn't support baseline SME instructions.

Make CONFIG_ARM64_SME depend on assembler support for SME, and remove
the manual encoding of SME instructions. The various _sme_<insn> macros
are kept for now, and will be cleaned up in subsequent patches.

A couple of SME2 instructions require a more recent toolchain, and are
left as-is for now. I've looked through releases of binutils and LLVM to
find when support was added, and noted this in a comment.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2026-06-03 12:06:20 +01:00 • committed by Will Deacon
commit db9d63eafe
2 changed files with 20 additions and 23 deletions
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