[U-Boot] [PATCH] mmc:dcache: Cache line size aligned internal MMC buffers

[Lukasz Majewski]

Hi Wolfgang,


> I think I'd like to see a macro that can be used like this:
> 
> 	void *dma_buffer_pointer = DMA_BUFFER(size_in_bytes);
> 

Frankly speaking I don't know any easy way to define buffer this way
in a macro (at least without digging deep enough to C preprocessor
programming tricks). Maybe Mike or Anton knows. 

The void *dma_buffer_pointer = DMA_BUFFER(size_in_bytes); approach 
needs to do following things in macro:

#define DMA_BUFFER(100) \
	char buf[100 + get_dcache_line_size]; \
	unsigned long tmp = (unsigned long) buf; \
	void* buf_out = (void*) ((tmp + (get_dcache_line_size() - 1)) &
	~(get_dcache_line_size() - 1))

The problem here is to assign the buf_out pointer to the void
*dma_buffer_pointer. How can we "return" the void *buf_out?





For comparison please look to this solution:

#define ALIGN_ADDR(addr) ((void *)(((unsigned long) addr +
get_dcache_line_size() - 1)\ & ~(get_dcache_line_size() - 1)))

#define DMA_DECLARE_BUFFER(type, name, size) \
	char *__##name[size + get_dcache_line_size()]; \
	type *name = ALIGN_ADDR(__##name);

int mmc_startup(struct mmc *mmc)
{
	/* Some declarations */
	/* char ext_csd[512]; */
	DMA_DECLARE_BUFFER(char, ext_csd, 512);

	printf("%s: ptr:%p\n", __func__, ext_csd);

	/* rest of the code */
}

Here the DMA_DECLARE_BUFFER really defines the buffer as an automatic 
variable with this function scope. This is tested and works :-)

> 
> > 4. get_dcache_line_size() can be simply defined as 
> > #define get_dcache_line_size() CONFIG_SYS_CACHE_LINE_SIZE if we
> > _really_ want to save a few bytes. 
> 
> Actually I fail to understand why we would ever need
> get_dcache_line_size() in a boot loader.

If I can ask for clarification here. 

Shall not u-boot read on fly the cache line size (as it is now done) or
you don't like the get_cache_line_size defined as function? 

Going further shall the get_cache_line_size be removed completely and
replaced with CONFIG_SYS_CACHE_LINE_SIZE?


> 
> Best regards,
> 
> Wolfgang Denk
> 



-- 
Best regards,

Lukasz Majewski

Samsung Poland R&D Center
Platform Group