On Thu, May 16, 2013 at 10:11:00AM -0400, Alan Stern wrote: > On Wed, 15 May 2013, Sarah Sharp wrote: > > > > If you're using 64-bit DMA then you almost certainly do want to call > > > dma_set_coherent_mask(). On the plus side, it is guaranteed that if > > > dma_set_mask() succeeds with a particular mask value then > > > dma_set_coherent_mask() for the same mask value will also succeed. > > > > So we need to call both dma_set_coherent_mask() and dma_set_mask()? Or > > just dma_set_coherent_mask()? > > It depends on what kind of DMA transfers you're going to do. For > streaming transfers (the ones that use dma_map_single() or > dma_map_sg(), for example), you need to call dma_set_mask(). For > coherent transfers (the ones that use dma_alloc_coherent() or > dma_pool_create()), you need to call dma_set_coherent_mask(). > > If you want to do both kinds of transfers then you need to call both > routines. I think we need the host to be able to do DMA to URB buffers that are mapped with dma_map_single() or dma_map_sg(), since that's what usb_hcd_submit_urb() uses. So the driver needs to call dma_set_mask(), which it does. The xHCI endpoint rings are allocated from DMA pools, so we need to call dma_set_coherent_mask() as well. Missing that call explains why I've never seen 64-bit endpoint rings, but I have seen 64-bit URB buffer pointers. Ksenia, do you want to add code to add the call to dma_set_coherent_mask() in those two places in xhci_gen_setup()? As I mentioned, let's add this function call first, and then have a separate commit refactor the copy-paste code into a new function. Again, thanks for catching this and asking questions! Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
