From: Mathias Nyman <mathias.nyman@linux.intel.com>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
Mathias Nyman <mathias.nyman@intel.com>
Cc: felipe.balbi@linux.intel.com, oneukum@suse.com,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: xhci: add Immediate Data Transfer support
Date: Tue, 19 Mar 2019 10:15:18 +0200 [thread overview]
Message-ID: <1fe79a10-16d4-8d06-4c9b-7e5a3d3807cf@linux.intel.com> (raw)
In-Reply-To: <31a3530dbd75771c82bfb41a357370b90d7981d2.camel@suse.de>
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
prev parent reply other threads:[~2019-03-19 8:13 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-19 16:29 [PATCH] usb: xhci: add Immediate Data Transfer support Nicolas Saenz Julienne
2019-02-20 9:30 ` Felipe Balbi
2019-03-15 12:51 ` Nicolas Saenz Julienne
2019-03-19 8:15 ` Mathias Nyman [this message]
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