On Tue, Oct 16, 2012 at 12:27:55PM +0200, Hiroshi Doyu wrote: > Hi Russell, > > Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote @ Tue, 16 Oct 2012 10:59:28 +0200: > > > 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. > > > > Remember that pages allocated into userspace will be cacheable, so a cache > > flush is required before they can be DMA'd. Hence the streaming > > API. > > Is the syscall "cacheflush()" supposed to be the knob for that? > > Or is there any other ones to have more precise control, "clean", > "invalidate" and "flush", from userland in generic way? No other syscalls are required - this sequence will do everything you need to perform DMA on pages mapped into userspace: get_user_pages() convert array of struct page * to scatterlist dma_map_sg() perform DMA dma_unmap_sg() for each page in sg() page_cache_release(page); If you get the list of pages some other way (eg, via shmem_read_mapping_page_gfp) then additional maintanence may be required (though that may be a bug in shmem - remember this stuff hasn't been well tested on ARM before.) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>