[PATCH v2 00/14] Unified cross-architecture kernel-mode FPU API

[Samuel Holland]

This series unifies the kernel-mode FPU API across several architectures
by wrapping the existing functions (where needed) in consistently-named
functions placed in a consistent header location, with mostly the same
semantics: they can be called from preemptible or non-preemptible task
context, and are not assumed to be reentrant. Architectures are also
expected to provide CFLAGS adjustments for compiling FPU-dependent code.
For the moment, SIMD/vector units are out of scope for this common API.

This allows us to remove the ifdeffery and duplicated Makefile logic at
each FPU user. It then implements the common API on RISC-V, and converts
a couple of users to the new API: the AMDGPU DRM driver, and the FPU
self test.

The underlying goal of this series is to allow using newer AMD GPUs
(e.g. Navi) on RISC-V boards such as SiFive's HiFive Unmatched. Those
GPUs need CONFIG_DRM_AMD_DC_FP to initialize, which requires kernel-mode
FPU support.

Previous versions:
v1: https://lore.kernel.org/linux-kernel/20231208055501.2916202-1-samuel.holland@sifive.com/
v0: https://lore.kernel.org/linux-kernel/20231122030621.3759313-1-samuel.holland@sifive.com/

Changes in v2:
 - Add documentation explaining the built-time and runtime APIs
 - Add a linux/fpu.h header for generic isolation enforcement
 - Remove file name from header comment
 - Clean up arch/arm64/lib/Makefile, like for arch/arm
 - Remove RISC-V architecture-specific preprocessor check
 - Split altivec removal to a separate patch
 - Use linux/fpu.h instead of asm/fpu.h in consumers
 - Declare test_fpu() in a header

Michael Ellerman (1):
  drm/amd/display: Only use hard-float, not altivec on powerpc

Samuel Holland (13):
  arch: Add ARCH_HAS_KERNEL_FPU_SUPPORT
  ARM: Implement ARCH_HAS_KERNEL_FPU_SUPPORT
  ARM: crypto: Use CC_FLAGS_FPU for NEON CFLAGS
  arm64: Implement ARCH_HAS_KERNEL_FPU_SUPPORT
  arm64: crypto: Use CC_FLAGS_FPU for NEON CFLAGS
  lib/raid6: Use CC_FLAGS_FPU for NEON CFLAGS
  LoongArch: Implement ARCH_HAS_KERNEL_FPU_SUPPORT
  powerpc: Implement ARCH_HAS_KERNEL_FPU_SUPPORT
  x86: Implement ARCH_HAS_KERNEL_FPU_SUPPORT
  riscv: Add support for kernel-mode FPU
  drm/amd/display: Use ARCH_HAS_KERNEL_FPU_SUPPORT
  selftests/fpu: Move FP code to a separate translation unit
  selftests/fpu: Allow building on other architectures

 Documentation/core-api/floating-point.rst     | 78 +++++++++++++++++++
 Documentation/core-api/index.rst              |  1 +
 Makefile                                      |  5 ++
 arch/Kconfig                                  |  6 ++
 arch/arm/Kconfig                              |  1 +
 arch/arm/Makefile                             |  7 ++
 arch/arm/include/asm/fpu.h                    | 15 ++++
 arch/arm/lib/Makefile                         |  3 +-
 arch/arm64/Kconfig                            |  1 +
 arch/arm64/Makefile                           |  9 ++-
 arch/arm64/include/asm/fpu.h                  | 15 ++++
 arch/arm64/lib/Makefile                       |  6 +-
 arch/loongarch/Kconfig                        |  1 +
 arch/loongarch/Makefile                       |  5 +-
 arch/loongarch/include/asm/fpu.h              |  1 +
 arch/powerpc/Kconfig                          |  1 +
 arch/powerpc/Makefile                         |  5 +-
 arch/powerpc/include/asm/fpu.h                | 28 +++++++
 arch/riscv/Kconfig                            |  1 +
 arch/riscv/Makefile                           |  3 +
 arch/riscv/include/asm/fpu.h                  | 16 ++++
 arch/riscv/kernel/Makefile                    |  1 +
 arch/riscv/kernel/kernel_mode_fpu.c           | 28 +++++++
 arch/x86/Kconfig                              |  1 +
 arch/x86/Makefile                             | 20 +++++
 arch/x86/include/asm/fpu.h                    | 13 ++++
 drivers/gpu/drm/amd/display/Kconfig           |  2 +-
 .../gpu/drm/amd/display/amdgpu_dm/dc_fpu.c    | 35 +--------
 drivers/gpu/drm/amd/display/dc/dml/Makefile   | 36 +--------
 drivers/gpu/drm/amd/display/dc/dml2/Makefile  | 36 +--------
 include/linux/fpu.h                           | 12 +++
 lib/Kconfig.debug                             |  2 +-
 lib/Makefile                                  | 26 +------
 lib/raid6/Makefile                            | 31 ++------
 lib/test_fpu.h                                |  8 ++
 lib/{test_fpu.c => test_fpu_glue.c}           | 37 ++-------
 lib/test_fpu_impl.c                           | 37 +++++++++
 37 files changed, 343 insertions(+), 190 deletions(-)
 create mode 100644 Documentation/core-api/floating-point.rst
 create mode 100644 arch/arm/include/asm/fpu.h
 create mode 100644 arch/arm64/include/asm/fpu.h
 create mode 100644 arch/powerpc/include/asm/fpu.h
 create mode 100644 arch/riscv/include/asm/fpu.h
 create mode 100644 arch/riscv/kernel/kernel_mode_fpu.c
 create mode 100644 arch/x86/include/asm/fpu.h
 create mode 100644 include/linux/fpu.h
 create mode 100644 lib/test_fpu.h
 rename lib/{test_fpu.c => test_fpu_glue.c} (71%)
 create mode 100644 lib/test_fpu_impl.c

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2.42.0