On Tue, 3 Jul 2012, Peter Stuge wrote:
> Hans de Goede wrote:
> > +++ b/drivers/usb/core/hcd.c
> > @@ -1389,7 +1389,12 @@ int usb_hcd_map_urb_for_dma(struct usb_hcd *hcd, struct urb *urb,
> > && !(urb->transfer_flags & URB_NO_TRANSFER_DMA_MAP)) {
> > if (hcd->self.uses_dma) {
> > if (urb->num_sgs) {
> > - int n = dma_map_sg(
> > + int n;
> > +
> > + /* We don't support sg for isoc transfers ! */
> > + BUG_ON(usb_endpoint_xfer_isoc(&urb->ep->desc));
>
> Again not very 2012. I'm not saying this is a must have right now,
> but I do think it is desirable. Isoc sg makes just as much sense to
> me as bulk sg, if not more. Yes may get interesting with empty
> buffers.
There's a good reason why isochronous transfers don't need this feature
so much. They _have_ to be limited in size, because they proceed at a
fixed rate and they can't extend too far into the future owing to
limitations in the host controller drivers.
> In any case, maybe add a comment about *why* isoc sg isn't supported.
A comment would be okay.
Alan Stern
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