On Thu, Aug 6, 2009 at 6:25 PM, Russell King - ARM Linux<li...@arm.linux.org.uk> wrote: [...] > As far as userspace DMA coherency, the only way you could do it with > current kernel APIs is by using get_user_pages(), creating a scatterlist > from those, and then passing it to dma_map_sg(). While the device has > ownership of the SG, userspace must _not_ touch the buffer until after > DMA has completed. [...]
Would that work on a processor with VIVT caches? It seems not. In particular, dma_map_page uses page_address to get a virtual address to pass to map_single(). map_single() in turn uses this address to perform cache maintenance. Since page_address() returns the kernel virtual address, I don't see how any cache-lines for the userspace virtual address would get invalidated (for the DMA_FROM_DEVICE case). If that's true, then what is the correct way to allow DMA to/from a userspace buffer with a VIVT cache? If not true, what am I missing? Thanks -- -Steven Walter <stevenrwal...@gmail.com> -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
