[RFC V4 2/3] arm:add bitrev.h file to support rbit instruction

["Wang, Yalin" <Yalin.Wang@xxxxxxxxxxxxxx>]

This patch add bitrev.h file to support rbit instruction,
so that we can do bitrev operation by hardware.
Signed-off-by: Yalin Wang <yalin.wang@xxxxxxxxxxxxxx>
---
 arch/arm/Kconfig              |  1 +
 arch/arm/include/asm/bitrev.h | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)
 create mode 100644 arch/arm/include/asm/bitrev.h

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 89c4b5c..be92b3b 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -28,6 +28,7 @@ config ARM
 	select HANDLE_DOMAIN_IRQ
 	select HARDIRQS_SW_RESEND
 	select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT)
+	select HAVE_ARCH_BITREVERSE if (CPU_V7M || CPU_V7)
 	select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_SECCOMP_FILTER if (AEABI && !OABI_COMPAT)
diff --git a/arch/arm/include/asm/bitrev.h b/arch/arm/include/asm/bitrev.h
new file mode 100644
index 0000000..c21a5f4
--- /dev/null
+++ b/arch/arm/include/asm/bitrev.h
@@ -0,0 +1,28 @@
+#ifndef __ASM_ARM_BITREV_H
+#define __ASM_ARM_BITREV_H
+
+static __always_inline __attribute_const__ u32 __arch_bitrev32(u32 x)
+{
+	if (__builtin_constant_p(x)) {
+		x = (x >> 16) | (x << 16);
+		x = ((x & 0xFF00FF00) >> 8) | ((x & 0x00FF00FF) << 8);
+		x = ((x & 0xF0F0F0F0) >> 4) | ((x & 0x0F0F0F0F) << 4);
+		x = ((x & 0xCCCCCCCC) >> 2) | ((x & 0x33333333) << 2);
+		return ((x & 0xAAAAAAAA) >> 1) | ((x & 0x55555555) << 1);
+	}
+	__asm__ ("rbit %0, %1" : "=r" (x) : "r" (x));
+	return x;
+}
+
+static __always_inline __attribute_const__ u16 __arch_bitrev16(u16 x)
+{
+	return __arch_bitrev32((u32)x) >> 16;
+}
+
+static __always_inline __attribute_const__ u8 __arch_bitrev8(u8 x)
+{
+	return __arch_bitrev32((u32)x) >> 24;
+}
+
+#endif
+
-- 
2.1.1
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