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

[Rob Herring]

On 12/17/2010 03:27 PM, Måns Rullgård wrote:
> 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.

This straight from the Linux code and there are only a few users of 
swab16 (none in my build).

Rob