[U-Boot] [PATCH] arm: Add armv6 and armv7 optimized swab functions

[Måns Rullgård]

Rob Herring <robherring2 at gmail.com> writes:

> From: Rob Herring <rob.herring at 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.herring at 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
mans at mansr.com