ARM: implement ARCH_HAS_KERNEL_FPU_SUPPORT

ARM provides an equivalent to the common kernel-mode FPU API, but in a
different header and using different function names.  Add a wrapper
header, and export CFLAGS adjustments as found in lib/raid6/Makefile.

[[email protected]: ARM: do not select ARCH_HAS_KERNEL_FPU_SUPPORT]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Samuel Holland <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Acked-by: Christian König <[email protected]> 
Cc: Alex Deucher <[email protected]>
Cc: Borislav Petkov (AMD) <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Masahiro Yamada <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Cc: Nicolas Schier <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Russell King <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: WANG Xuerui <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Thiago Jung Bauermann <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: SiFiveHolland

arch/arm/Makefile

@@ -130,6 +130,13 @@ endif
 # Accept old syntax despite ".syntax unified"
 AFLAGS_NOWARN	:=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
 
+# The GCC option -ffreestanding is required in order to compile code containing
+# ARM/NEON intrinsics in a non C99-compliant environment (such as the kernel)
+CC_FLAGS_FPU	:= -ffreestanding
+# Enable <arm_neon.h>
+CC_FLAGS_FPU	+= -isystem $(shell $(CC) -print-file-name=include)
+CC_FLAGS_FPU	+= -march=armv7-a -mfloat-abi=softfp -mfpu=neon
+
 ifeq ($(CONFIG_THUMB2_KERNEL),y)
 CFLAGS_ISA	:=-Wa,-mimplicit-it=always $(AFLAGS_NOWARN)
 AFLAGS_ISA	:=$(CFLAGS_ISA) -Wa$(comma)-mthumb

arch/arm/include/asm/fpu.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023 SiFive
+ */
+
+#ifndef __ASM_FPU_H
+#define __ASM_FPU_H
+
+#include <asm/neon.h>
+
+#define kernel_fpu_available()	cpu_has_neon()
+#define kernel_fpu_begin()	kernel_neon_begin()
+#define kernel_fpu_end()	kernel_neon_end()
+
+#endif /* ! __ASM_FPU_H */