[RFC V4 1/3] add CONFIG_HAVE_ARCH_BITREVERSE to support rbit instruction

[Wang, Yalin]

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

We also change byte_rev_table[] to be static,
to make sure no drivers can access it directly.

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

Signed-off-by: Yalin Wang <yalin.w...@sonymobile.com>
---
 include/linux/bitrev.h | 21 ++++++++++++++++++---
 lib/Kconfig            |  9 +++++++++
 lib/bitrev.c           | 19 +++----------------
 3 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/include/linux/bitrev.h b/include/linux/bitrev.h
index 7ffe03f..fa2682c 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
 
 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..ba13610 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>
@@ -6,7 +7,7 @@ MODULE_AUTHOR("Akinobu Mita <akinobu.m...@gmail.com>");
 MODULE_DESCRIPTION("Bit ordering reversal functions");
 MODULE_LICENSE("GPL");
 
-const u8 byte_rev_table[256] = {
+const static u8 byte_rev_table[256] = {
        0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0,
        0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0,
        0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8,
@@ -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

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