On Monday, September 12, 2016 9:09:16 AM CEST Alan Stern wrote: > > diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c > > index 0406a59..66364ea 100644 > > --- a/drivers/usb/core/message.c > > +++ b/drivers/usb/core/message.c > > @@ -1863,6 +1863,12 @@ free_interfaces: > > intf->dev.type = &usb_if_device_type; > > intf->dev.groups = usb_interface_groups; > > intf->dev.dma_mask = dev->dev.dma_mask; > > + /* Propagate dma_pfn_offset to USB interface. > > + * This is especially required by mass storage interface > > + * which relies on SCSI layer and scsi_calculate_bounce_limit() > > + * to set the bounce buffer limit based on dma_pfn_offset. > > + */ > > + intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset; > > I really think this comment isn't necessary. It seems pretty obvious > that if you're copying DMA-related fields from one device to another > then you'll want to copy the dma_pfn_offset along with everything else. > No? > > The explanation in the Changelog is enough, IMO. I asked for a code comment here as what we are doing here is a bit fishy, but the comment (evidently) doesn't quite capture it. I would add (above the dma_mask assignment) something like /* * Fake a dma_mask/offset for the USB device: * We cannot really use the dma-mapping API (dma_alloc_* and * dma_map_*) for USB devices but instead need to use * usb_alloc_coherent and pass data in 'urb's, but some subsystems * manually look into the mask/offset pair to determine whether * they need bounce buffers. * Note: calling dma_set_mask() on a USB device would set the * mask for the entire HCD, so don't do that. */ Arnd -- 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
