On Mon, Jun 01, 2009 at 06:32:44PM +0900, FUJITA Tomonori wrote: > Can ARM replace the dmabounce with swiotlb? We could, if there was some effort with swiotlb to make it safe on non-cache coherent architectures. As it stands, it sources its memory from __get_free_pages() which is non-coherent on ARM. There's nothing wrong with that per-se, provided we use the streaming DMA mapping API on those pages and obey the buffer ownership rules. Also, it needs cache flushing - one thing davem said to me a while back is that the effects of DMA should be the same as far as the cache is concerned no matter how it is performed. In other words, from the external perspective: dma_map_single() hardware DMA happens dma_unmap_single() should result in exactly the same situation on an architecture as far as the buffer is concerned no matter what the underlying implementation is. So, on a non-DMA coherent cache architecture, when DMA is normally performed the data ends up in RAM with the cache flushed for that region. If, instead dma_map_single uses a bounce buffer to do that DMA, then the same needs to be true of the original buffer - the data needs to be in RAM with the cache flushed. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
