[U-Boot] [PATCH v2] ARM926ejs: Add routines to invalidate D-Cache

[Albert ARIBAUD <albert.u.boot@aribaud.net>]

Hi Hong Xu,

Le 05/08/2011 06:44, Hong Xu a ?crit :
> After DMA operation, we need to maintain D-Cache coherency.
> We need to clean cache (write back the dirty lines) and then
> make the cache invalidate as well(hence CPU will fetch data
> written by DMA controller from RAM).
>
> Tested on AT91SAM9261EK with Peripheral DMA controller.
>
> Signed-off-by: Hong Xu<hong.xu@atmel.com>
> Tested-by: Elen Song<elen.song@atmel.com>
> CC: Albert Aribaud<albert.aribaud@free.fr>
> CC: Heiko Schocher<hs@denx.de>
> ---
> Changes since v1
> ~ Per Albert's suggestion, add invalidate_dcache_range originally defined
>    in include/common.h
>
>   arch/arm/lib/cache.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
>   1 files changed, 46 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm/lib/cache.c b/arch/arm/lib/cache.c
> index 92b61a2..0436443 100644
> --- a/arch/arm/lib/cache.c
> +++ b/arch/arm/lib/cache.c
> @@ -53,3 +53,49 @@ void	__flush_dcache_all(void)
>   }
>   void	flush_dcache_all(void)
>   	__attribute__((weak, alias("__flush_dcache_all")));
> +
> +void __invalidate_dcache_range(unsigned long start, unsigned long stop)
> +{
> +	int cache_line_len;
> +	unsigned long mva;
> +
> +#ifdef CONFIG_ARM926EJS
> +
> +#ifdef CONFIG_SYS_CACHELINE_SIZE
> +	cache_line_len = CONFIG_SYS_CACHELINE_SIZE;
> +#else
> +	cache_line_len = 32;

Document magic number 32 -- for instance, indicate ARM architecture spec 
paragraph reference in a comment above it (and possibly emit a 
compile-time and/or run-time warning) -- or bail out with a compile 
error if CONFIG_SYS_CACHELINE_SIZE is not defined.

> +#endif
> +	/*
> +	 * If start and stop are not aligned to cache-line,
> +	 * the adjacent lines will be cleaned
> +	 */
> +	if ((start&  (cache_line_len - 1)) != 0)
> +		asm("mcr p15, 0, %0, c7, c10, 1" : : "r" (start));
> +	if ((stop&  (cache_line_len - 1)) != 0)
> +		asm("mcr p15, 0, %0, c7, c10, 1" : : "r" (stop));
> +
> +	mva = start&  ~(cache_line_len - 1);
> +	while (mva<  stop) {
> +		asm("mcr p15, 0, %0, c7, c6, 1" : : "r"(mva));
> +		mva += cache_line_len;
> +	}

I, like Reinhard, prefer aligning start and stop and then looping 
through a single invalidate mcr.

But I also want to make sure logs tell us anything weird with caches, 
and since unaligned start or stop invalidation could lead to trashing 
third party data, I would like the code to emit a run-time warning if 
that happens, like this:

   if ((start&  (cache_line_len - 1)) != 0) {
     printf("WARNING: aligning start %x on start of cache line\n",
       start);
     start &= ~(cache_line_len - 1);
   }
   if ((stop&  (cache_line_len - 1)) != (cache_line_len -1) ) {
     printf("WARNING: aligning stop %x on end of cache line\n",
       stop);
     start |= (cache_line_len - 1);
   }

That will guarantee that unaligned cache invalidates will be detectable, 
and/or that will entice developers to align their starts and stops.

> +	/* Drain the WB */
> +	asm("mcr p15, 0, %0, c7, c10, 4" : : "r" (0));
> +#endif
> +
> +	return;
> +}
> +void invalidate_dcache_range(unsigned long start, unsigned long stop)
> +	__attribute__((weak, alias("__invalidate_dcache_range")));
> +
> +void __invalidate_dcache_all(void)
> +{
> +#ifdef CONFIG_ARM926EJS
> +	asm("mcr p15, 0, %0, c7, c6, 0" : : "r" (0));
> +#endif
> +	return;
> +}
> +void  invalidate_dcache_all(void)
> +	__attribute__((weak, alias("__invalidate_dcache_all")));

Amicalement,
-- 
Albert.