[RFC PATCH 2/2] ARM: dcache: select DCACHE_WORD_ACCESS for little-endian ARMv6+ CPUs

[Nicolas Pitre]

On Fri, 8 Jun 2012, Will Deacon wrote:

> DCACHE_WORD_ACCESS uses the word-at-a-time API for optimised string
> comparisons in the vfs layer.
> 
> This patch implements support for load_unaligned_zeropad for ARM CPUs
> with native support for unaligned memory accesses (v6+) when running
> little-endian.
> 
> Signed-off-by: Will Deacon <will.deacon at arm.com>

Reviewed-by: Nicolas Pitre <nico at linaro.org>

> ---
>  arch/arm/Kconfig                      |    1 +
>  arch/arm/include/asm/word-at-a-time.h |   41 +++++++++++++++++++++++++++++++++
>  2 files changed, 42 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index b236fd9..9e7b51f 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -48,6 +48,7 @@ config ARM
>  	select GENERIC_CLOCKEVENTS_BROADCAST if SMP
>  	select GENERIC_STRNCPY_FROM_USER
>  	select GENERIC_STRNLEN_USER
> +	select DCACHE_WORD_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && !CPU_BIG_ENDIAN
>  	help
>  	  The ARM series is a line of low-power-consumption RISC chip designs
>  	  licensed by ARM Ltd and targeted at embedded applications and
> diff --git a/arch/arm/include/asm/word-at-a-time.h b/arch/arm/include/asm/word-at-a-time.h
> index 74b2d45..4d52f92 100644
> --- a/arch/arm/include/asm/word-at-a-time.h
> +++ b/arch/arm/include/asm/word-at-a-time.h
> @@ -48,6 +48,47 @@ static inline unsigned long find_zero(unsigned long mask)
>  	return ret;
>  }
>  
> +#ifdef CONFIG_DCACHE_WORD_ACCESS
> +
> +#define zero_bytemask(mask) (mask)
> +
> +/*
> + * Load an unaligned word from kernel space.
> + *
> + * In the (very unlikely) case of the word being a page-crosser
> + * and the next page not being mapped, take the exception and
> + * return zeroes in the non-existing part.
> + */
> +static inline unsigned long load_unaligned_zeropad(const void *addr)
> +{
> +	unsigned long ret, offset;
> +
> +	/* Load word from unaligned pointer addr */
> +	asm(
> +	"1:	ldr	%0, [%2]\n"
> +	"2:\n"
> +	"	.pushsection .fixup,\"ax\"\n"
> +	"	.align 2\n"
> +	"3:	and	%1, %2, #0x3\n"
> +	"	bic	%2, %2, #0x3\n"
> +	"	ldr	%0, [%2]\n"
> +	"	lsl	%1, %1, #0x3\n"
> +	"	lsr	%0, %0, %1\n"
> +	"	b	2b\n"
> +	"	.popsection\n"
> +	"	.pushsection __ex_table,\"a\"\n"
> +	"	.align	3\n"
> +	"	.long	1b, 3b\n"
> +	"	.popsection"
> +	: "=&r" (ret), "=&r" (offset)
> +	: "r" (addr), "Qo" (*(unsigned long *)addr));
> +
> +	return ret;
> +}
> +
> +
> +#endif	/* DCACHE_WORD_ACCESS */
> +
>  #else	/* __ARMEB__ */
>  #include <asm-generic/word-at-a-time.h>
>  #endif
> -- 
> 1.7.4.1
> 
> 
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