[RFC V5 1/3] add CONFIG_HAVE_ARCH_BITREVERSE to support rbit instruction

["Wang, Yalin" <Yalin.Wang@sonymobile.com>]

this change add CONFIG_HAVE_ARCH_BITREVERSE config option,
so that we can use arm/arm64 rbit instruction to do bitrev operation
by hardware.

Change bitrev16() bitrev32() to be inline function,
don't need export symbol for these tiny functions.

Signed-off-by: Yalin Wang <yalin.wang@sonymobile.com>
---
 include/linux/bitrev.h | 21 ++++++++++++++++++---
 lib/Kconfig            |  9 +++++++++
 lib/bitrev.c           | 17 ++---------------
 3 files changed, 29 insertions(+), 18 deletions(-)

diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h
index 7ffe03f..413c52c 100644
--- a/include/linux/bitrev.h
+++ b/include/linux/bitrev.h
@@ -3,14 +3,29 @@
 
 #include <linux/types.h>
 
-extern u8 const byte_rev_table[256];
+#ifdef CONFIG_HAVE_ARCH_BITREVERSE
+#include <asm/bitrev.h>
+
+#define bitrev32 __arch_bitrev32
+#define bitrev16 __arch_bitrev16
+#define bitrev8 __arch_bitrev8
 
+#else
+extern u8 const byte_rev_table[256];
 static inline u8 bitrev8(u8 byte)
 {
 	return byte_rev_table[byte];
 }
 
-extern u16 bitrev16(u16 in);
-extern u32 bitrev32(u32 in);
+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);
+}
 
+#endif /* CONFIG_HAVE_ARCH_BITREVERSE */
 #endif /* _LINUX_BITREV_H */
diff --git a/lib/Kconfig b/lib/Kconfig
index 54cf309..cd177ca 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -13,6 +13,15 @@ config RAID6_PQ
 config BITREVERSE
 	tristate
 
+config HAVE_ARCH_BITREVERSE
+	boolean
+	default n
+	depends on BITREVERSE
+	help
+	  This option provides an config for the architecture which have instruction
+	  can do bitreverse operation, we use the hardware instruction if the architecture
+	  have this capability.
+
 config RATIONAL
 	boolean
 
diff --git a/lib/bitrev.c b/lib/bitrev.c
index 3956203..40ffda9 100644
--- a/lib/bitrev.c
+++ b/lib/bitrev.c
@@ -1,3 +1,4 @@
+#ifndef CONFIG_HAVE_ARCH_BITREVERSE
 #include <linux/types.h>
 #include <linux/module.h>
 #include <linux/bitrev.h>
@@ -42,18 +43,4 @@ const u8 byte_rev_table[256] = {
 };
 EXPORT_SYMBOL_GPL(byte_rev_table);
 
-u16 bitrev16(u16 x)
-{
-	return (bitrev8(x & 0xff) << 8) | bitrev8(x >> 8);
-}
-EXPORT_SYMBOL(bitrev16);
-
-/**
- * bitrev32 - reverse the order of bits in a u32 value
- * @x: value to be bit-reversed
- */
-u32 bitrev32(u32 x)
-{
-	return (bitrev16(x & 0xffff) << 16) | bitrev16(x >> 16);
-}
-EXPORT_SYMBOL(bitrev32);
+#endif /* CONFIG_HAVE_ARCH_BITREVERSE */
-- 
2.1.1