On 16 October 2012 09:59, Russell King - ARM Linux
[off-list ref] wrote:

On Tue, Oct 16, 2012 at 09:04:34AM +0300, Hiroshi Doyu wrote:

quoted

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().

-- 
Catalin