On Mon, Oct 27, 2014 at 08:02:08AM +0000, Wang, Yalin wrote:
> this change add CONFIG_HAVE_ARCH_BITREVERSE config option,
> so that we can use arm/arm64 rbit instruction to do bitrev operation
> by hardware.
>
> Signed-off-by: Yalin Wang <yalin.wang@xxxxxxxxxxxxxx>
> ---
> arch/arm/Kconfig | 1 +
> arch/arm/include/asm/bitrev.h | 28 ++++++++++++++++++++++++++++
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/bitrev.h | 28 ++++++++++++++++++++++++++++
> include/linux/bitrev.h | 9 +++++++++
> lib/Kconfig | 9 +++++++++
> lib/bitrev.c | 2 ++
> 7 files changed, 78 insertions(+)
> create mode 100644 arch/arm/include/asm/bitrev.h
> create mode 100644 arch/arm64/include/asm/bitrev.h
>
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 89c4b5c..426cbcc 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -16,6 +16,7 @@ config ARM
> select DCACHE_WORD_ACCESS if HAVE_EFFICIENT_UNALIGNED_ACCESS
> select GENERIC_ALLOCATOR
> select GENERIC_ATOMIC64 if (CPU_V7M || CPU_V6 || !CPU_32v6K || !AEABI)
> + select HAVE_ARCH_BITREVERSE if (CPU_V7M || CPU_V7)
> select GENERIC_CLOCKEVENTS_BROADCAST if SMP
> select GENERIC_IDLE_POLL_SETUP
> select GENERIC_IRQ_PROBE
> 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));
I think you need to use %w0 and %w1 here, otherwise you bit-reverse the
64-bit register.
Will
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