>> This is called when we submit urb, for OUT data, I think it's 
quoted text
>> sufficient for cache consistency. But what I need to know is how we 
>> guarantee the cache consistency for IN data, because the DMA is going

quoted text
>> to update the physical memory when receiving data from device, 
>> something has to be done upon completion of the urb.

quoted text
>Obviously you looked at map_urb_for_dma.  Have you also looked at
unmap_urb_for_dma?

unmap_urb_for_dma -> dma_unmap_single

dma_unmap_single is defined in arch/arm/include/asm/dma-mapping.h as
following

------ snip ------
#ifndef CONFIG_DMABOUNCE
static inline void
dma_unmap_single(struct device *dev, dma_addr_t handle, size_t size,
		 enum dma_data_direction dir)
{
	/* nothing to do */
}
#else
extern void dma_unmap_single(struct device *, dma_addr_t, size_t, enum
dma_data_direction);
#endif
------ snip ------

And CONFIG_DMABOUNCE is not defined in the defconfig.

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