Hi Russell, On Thu, 31 Mar 2016 15:14:13 +0100 Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: > On Thu, Mar 31, 2016 at 02:29:42PM +0200, Boris Brezillon wrote: > > sg_alloc_table_from_buf() provides an easy solution to create an sg_table > > from a virtual address pointer. This function takes care of dealing with > > vmallocated buffers, buffer alignment, or DMA engine limitations (maximum > > DMA transfer size). > > Please note that the DMA API does not take account of coherency of memory > regions other than non-high/lowmem - there are specific extensions to > deal with this. Ok, you said 'non-high/lowmem', this means vmalloced and kmapped buffers already fall in this case, right? Could you tell me more about those specific extensions? > > What this means is that having an API that takes any virtual address > pointer, converts it to a scatterlist which is then DMA mapped, is > unsafe. Which means some implementations already get this wrong (see spi_map_buf(), and I'm pretty sure it's not the only one). > > It'll be okay for PIPT and non-aliasing VIPT cache architectures, but > for other cache architectures this will hide this problem and make > review harder. > Ok, you lost me. I'll have to do my homework and try to understand what this means :). Thanks for your valuable inputs. Best Regards, Boris -- Boris Brezillon, Free Electrons Embedded Linux and Kernel engineering http://free-electrons.com -- 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>