[PATCH v4 1/2] bitops: Define generic __bitrev8/16/32 for reuse

[Jinjie Ruan]

Define generic __bitrev8/16/32 using the implementation
in <linux/bitrev.h>, so they can be reused in <asm/bitrev.h>,
such as RISCV.

And introduce a NEED_BYTE_REVERSE_TABLE Kconfig option, so byte_rev_table
is only compiled when !HAVE_ARCH_BITREVERSE or when an architecture (like
RISC-V) explicitly selects it as a fallback. This avoids bloating the .data
section for architectures that have full hardware bit-reverse support and
don't need the table.

Reviewed-by: Yury Norov <ynorov at nvidia.com>
Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
 include/asm-generic/bitops/__bitrev.h | 25 +++++++++++++++++++++++++
 include/linux/bitrev.h                | 20 ++++----------------
 lib/Kconfig                           |  4 ++++
 lib/bitrev.c                          |  4 ++--
 4 files changed, 35 insertions(+), 18 deletions(-)
 create mode 100644 include/asm-generic/bitops/__bitrev.h

diff --git a/include/asm-generic/bitops/__bitrev.h b/include/asm-generic/bitops/__bitrev.h
new file mode 100644
index 000000000000..9d7d3d369364
--- /dev/null
+++ b/include/asm-generic/bitops/__bitrev.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_BITOPS___BITREV_H_
+#define _ASM_GENERIC_BITOPS___BITREV_H_
+
+#ifdef CONFIG_NEED_BYTE_REVERSE_TABLE
+#include <asm/types.h>
+
+extern u8 const byte_rev_table[256];
+static __always_inline __attribute_const__ u8 generic___bitrev8(u8 byte)
+{
+	return byte_rev_table[byte];
+}
+
+static __always_inline __attribute_const__ u16 generic___bitrev16(u16 x)
+{
+	return (generic___bitrev8(x & 0xff) << 8) | generic___bitrev8(x >> 8);
+}
+
+static __always_inline __attribute_const__ u32 generic___bitrev32(u32 x)
+{
+	return (generic___bitrev16(x & 0xffff) << 16) | generic___bitrev16(x >> 16);
+}
+#endif /* CONFIG_NEED_BYTE_REVERSE_TABLE */
+
+#endif /* _ASM_GENERIC_BITOPS___BITREV_H_ */
diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h
index d35b8ec1c485..11620a70e776 100644
--- a/include/linux/bitrev.h
+++ b/include/linux/bitrev.h
@@ -12,22 +12,10 @@
 #define __bitrev8 __arch_bitrev8
 
 #else
-extern u8 const byte_rev_table[256];
-static inline u8 __bitrev8(u8 byte)
-{
-	return byte_rev_table[byte];
-}
-
-static inline u16 __bitrev16(u16 x)
-{
-	return (__bitrev8(x & 0xff) << 8) | __bitrev8(x >> 8);
-}
-
-static inline u32 __bitrev32(u32 x)
-{
-	return (__bitrev16(x & 0xffff) << 16) | __bitrev16(x >> 16);
-}
-
+#include <asm-generic/bitops/__bitrev.h>
+#define __bitrev32 generic___bitrev32
+#define __bitrev16 generic___bitrev16
+#define __bitrev8 generic___bitrev8
 #endif /* CONFIG_HAVE_ARCH_BITREVERSE */
 
 #define __bitrev8x4(x)	(__bitrev32(swab32(x)))
diff --git a/lib/Kconfig b/lib/Kconfig
index 0f2fb9610647..75cbb647b1da 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -62,6 +62,10 @@ config HAVE_ARCH_BITREVERSE
 	  This option enables the use of hardware bit-reversal instructions on
 	  architectures which support such operations.
 
+config NEED_BYTE_REVERSE_TABLE
+	bool
+	default y if !HAVE_ARCH_BITREVERSE
+
 config ARCH_HAS_STRNCPY_FROM_USER
 	bool
 
diff --git a/lib/bitrev.c b/lib/bitrev.c
index 81b56e0a7f32..d9d5ee00229c 100644
--- a/lib/bitrev.c
+++ b/lib/bitrev.c
@@ -1,5 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0-only
-#ifndef CONFIG_HAVE_ARCH_BITREVERSE
+#ifdef CONFIG_NEED_BYTE_REVERSE_TABLE
 #include <linux/types.h>
 #include <linux/module.h>
 #include <linux/bitrev.h>
@@ -44,4 +44,4 @@ const u8 byte_rev_table[256] = {
 };
 EXPORT_SYMBOL_GPL(byte_rev_table);
 
-#endif /* CONFIG_HAVE_ARCH_BITREVERSE */
+#endif /* CONFIG_NEED_BYTE_REVERSE_TABLE */
-- 
2.34.1