>> I want to allocate a contiguous 8MB buffer and use it for streaming DMA. I >> don't need or want >> a coherent buffer, since I'm using streaming DMA, and so >> dma_alloc_coherent() seems like >> the wrong method to use. Is that true, or should I use it anyway? If not, >> what method do I use? >> >> The DMA-API and DMA-API-HOWTO documents don't seem to say anything about >> allocating >> memory for streaming DMA operations. Have I missed something?
On Mon, Jan 6, 2014 at 1:29 AM, saumendra dash <[email protected]> wrote: > > For streaming DMA, you can use the function dma_map_single(). > Alternatively, you can create your own DMA pool using dma_pool_create(), and > allocate memory from that using dma_pool_alloc((). > > The later case will be more suitable for you, since you want a 8MB DMA buffer > for your DMA. > Hope that helps/ I am using dma_map_single, but it doesn't allocate any memory. From what I understand, it takes a pointer to a buffer and performs the necessary cache flushes or invalidations to make sure that the memory is safe to DMA. Is there a correct way to allocate large buffers for streaming DMA? Right now, I'm allocating memory with get_free_pages, but that is prone to fail on large allocations, and only works up to 4MB on my system (i.e get_free_pages order 10). >From reading LDD3 and DMA-API.txt, DMA pools are for allocating "small dma-coherent memory regions". LDD3 specifically states that pools are useful where the driver needs regions smaller than 1 page. Since I want large, non-coherent buffers, I don't see how this helps. Steven _______________________________________________ Kernelnewbies mailing list [email protected] http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
