Rob Herring <robherri...@gmail.com> writes:
> From: Rob Herring <rob.herr...@calxeda.com>
>
> swab functions are heavily used by FDT code, so enable
> optimized assembly code for ARMv6 and later.
>
> Signed-off-by: Rob Herring <rob.herr...@calxeda.com>
> ---
> arch/arm/include/asm/byteorder.h | 16 ++++++++++++++++
> 1 files changed, 16 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/include/asm/byteorder.h
> b/arch/arm/include/asm/byteorder.h
> index c3489f1..9df5844 100644
> --- a/arch/arm/include/asm/byteorder.h
> +++ b/arch/arm/include/asm/byteorder.h
> @@ -23,6 +23,22 @@
> # define __SWAB_64_THRU_32__
> #endif
>
> +#if defined(__ARM_ARCH_7A__) || defined(__ARM_ARCH_6__)
> +static inline __u16 __attribute__((const)) ___arch_swab16(__u16 x)
> +{
> + __asm__ ("rev16 %0, %1" : "=r" (x) : "r" (x));
> + return x;
> +}
Pay close attention to what gcc does with this as it is prone to add
unnecessary masking of the low halfword. If the callers are
well-behaved (argument having top halfword clear), making the
parameter and return types here plain unsigned (or u32) gives better
code.
--
Måns Rullgård
m...@mansr.com
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