riscv: introduce asm/swab.h

Implement endianness swap macros for RISC-V. Use the rev8 instruction when Zbb is available. Otherwise, rely on the default mask-and-shift implementation. Acked-by: Palmer Dabbelt <palmer@rivosinc.com> Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Tested-by: Alexandre Ghiti <alexghiti@rivosinc.com> Signed-off-by: Ignacio Encinas <ignacio@iencinas.com> Link: https://lore.kernel.org/r/20250723-riscv-swab-v6-1-fc11e9a2efc9@iencinas.com Signed-off-by: Paul Walmsley <pjw@kernel.org>
2025-09-18 08:20:25 -06:00
parent 316b60b984
commit cc2294d3f9
1 changed files with 87 additions and 0 deletions
@@ -0,0 +1,87 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _ASM_RISCV_SWAB_H
+#define _ASM_RISCV_SWAB_H
+
+#include <linux/types.h>
+#include <linux/compiler.h>
+#include <asm/cpufeature-macros.h>
+#include <asm/hwcap.h>
+#include <asm-generic/swab.h>
+
+#if defined(CONFIG_TOOLCHAIN_HAS_ZBB) && defined(CONFIG_RISCV_ISA_ZBB) && !defined(NO_ALTERNATIVE)
+
+// Duplicated from include/uapi/linux/swab.h
+#define ___constant_swab16(x) ((__u16)(				\
+	(((__u16)(x) & (__u16)0x00ffU) << 8) |			\
+	(((__u16)(x) & (__u16)0xff00U) >> 8)))
+
+#define ___constant_swab32(x) ((__u32)(				\
+	(((__u32)(x) & (__u32)0x000000ffUL) << 24) |		\
+	(((__u32)(x) & (__u32)0x0000ff00UL) <<  8) |		\
+	(((__u32)(x) & (__u32)0x00ff0000UL) >>  8) |		\
+	(((__u32)(x) & (__u32)0xff000000UL) >> 24)))
+
+#define ___constant_swab64(x) ((__u64)(				\
+	(((__u64)(x) & (__u64)0x00000000000000ffULL) << 56) |	\
+	(((__u64)(x) & (__u64)0x000000000000ff00ULL) << 40) |	\
+	(((__u64)(x) & (__u64)0x0000000000ff0000ULL) << 24) |	\
+	(((__u64)(x) & (__u64)0x00000000ff000000ULL) <<  8) |	\
+	(((__u64)(x) & (__u64)0x000000ff00000000ULL) >>  8) |	\
+	(((__u64)(x) & (__u64)0x0000ff0000000000ULL) >> 24) |	\
+	(((__u64)(x) & (__u64)0x00ff000000000000ULL) >> 40) |	\
+	(((__u64)(x) & (__u64)0xff00000000000000ULL) >> 56)))
+
+#define ARCH_SWAB(size, value)						\
+({									\
+	unsigned long x = value;					\
+									\
+	if (riscv_has_extension_likely(RISCV_ISA_EXT_ZBB)) {            \
+		asm volatile (".option push\n"				\
+			      ".option arch,+zbb\n"			\
+			      "rev8 %0, %1\n"				\
+			      ".option pop\n"				\
+			      : "=r" (x) : "r" (x));			\
+		x = x >> (BITS_PER_LONG - size);			\
+	} else {                                                        \
+		x = ___constant_swab##size(value);                      \
+	}								\
+	x;								\
+})
+
+static __always_inline __u16 __arch_swab16(__u16 value)
+{
+	return ARCH_SWAB(16, value);
+}
+
+static __always_inline __u32 __arch_swab32(__u32 value)
+{
+	return ARCH_SWAB(32, value);
+}
+
+#ifdef CONFIG_64BIT
+static __always_inline __u64 __arch_swab64(__u64 value)
+{
+	return ARCH_SWAB(64, value);
+}
+#else
+static __always_inline __u64 __arch_swab64(__u64 value)
+{
+	__u32 h = value >> 32;
+	__u32 l = value & ((1ULL << 32) - 1);
+
+	return ((__u64)(__arch_swab32(l)) << 32) | ((__u64)(__arch_swab32(h)));
+}
+#endif
+
+#define __arch_swab64 __arch_swab64
+#define __arch_swab32 __arch_swab32
+#define __arch_swab16 __arch_swab16
+
+#undef ___constant_swab16
+#undef ___constant_swab32
+#undef ___constant_swab64
+
+#undef ARCH_SWAB
+
+#endif /* defined(CONFIG_TOOLCHAIN_HAS_ZBB) && defined(CONFIG_RISCV_ISA_ZBB) && !defined(NO_ALTERNATIVE) */
+#endif /* _ASM_RISCV_SWAB_H */