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Date: Tue, 19 Mar 2019 10:15:18 +0200 From: Mathias Nyman <mathias.nyman@...ux.intel.com> To: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>, Mathias Nyman <mathias.nyman@...el.com> Cc: felipe.balbi@...ux.intel.com, oneukum@...e.com, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] usb: xhci: add Immediate Data Transfer support 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@...e.de> > > > Friendly ping, any more comments on this? :) > Looks good, adding to queue, thanks -Mathias
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