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SubjectRe: [PATCH] usb: xhci: add Immediate Data Transfer support
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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@suse.de>
>
>
> Friendly ping, any more comments on this? :)
>

Looks good, adding to queue, thanks

-Mathias

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