On 16 October 2012 09:59, Russell King - ARM Linux linux@arm.linux.org.uk wrote:
On Tue, Oct 16, 2012 at 09:04:34AM +0300, Hiroshi Doyu wrote:
In addition to those contiguous/discontiguous page allocation, is there any way to _import_ anonymous pages allocated by a process to be used in dma-mapping API later?
I'm considering the following scenario, an user process allocates a buffer by malloc() in advance, and then it asks some driver to convert that buffer into IOMMU'able/DMA'able ones later. In this case, pages are discouguous and even they may not be yet allocated at malloc()/mmap().
That situation is covered. It's the streaming API you're wanting for that. dma_map_sg() - but you may need additional cache handling via flush_dcache_page() to ensure that your code is safe for all CPU cache architectures.
For user-allocated pages you first need get_user_pages() to make sure they are in memory (and will stay there). This function also calls flush_dcache_page(). Then you can build the sg list for dma_map_sg().