Re: [PATCH] usb: xhci: add Immediate Data Transfer support

[Mathias Nyman]

On 15.3.2019 14.51, Nicolas Saenz Julienne wrote:
> On Tue, 2019-02-19 at 17:29 +0100, Nicolas Saenz Julienne wrote:
> > Immediate data transfers (IDT) allow the HCD to copy small chunks of
> > data (up to 8bytes) directly into its output transfer TRBs. This avoids
> > the somewhat expensive DMA mappings that are performed by default on
> > most URBs submissions.
> >
> > In the case an URB was suitable for IDT. The data is directly copied
> > into the "Data Buffer Pointer" region of the TRB and the IDT flag is
> > set. Instead of triggering memory accesses the HC will use the data
> > directly.
> >
> > The implementation could cover all kind of output endpoints. Yet
> > Isochronous endpoints are bypassed as I was unable to find one that
> > matched IDT's constraints. As we try to bypass the default DMA mappings
> > on URB buffers we'd need to find a Isochronous device with an
> > urb->transfer_buffer_length <= 8 bytes.
> >
> > The implementation takes into account that the 8 byte buffers provided
> > by the URB will never cross a 64KB boundary.
> >
> > Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
>
>
> Friendly ping, any more comments on this? :)

Looks good, adding to queue, thanks

-Mathias