From: Felipe Balbi <felipe.balbi@linux.intel.com>
To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
Mathias Nyman <mathias.nyman@intel.com>
Cc: oneukum@suse.com, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: usb: xhci: add Immediate Data Transfer support
Date: Wed, 20 Feb 2019 11:30:28 +0200 [thread overview]
Message-ID: <87ftsidcy3.fsf@linux.intel.com> (raw)
Nicolas Saenz Julienne <nsaenzjulienne@suse.de> writes:
> 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>
This looks good to my eyes.
Reviewed-by: Felipe Balbi <felipe.balbi@linux.intel.com>
next reply other threads:[~2019-02-20 9:30 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-20 9:30 Felipe Balbi [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-03-19 8:15 usb: xhci: add Immediate Data Transfer support Mathias Nyman
2019-03-15 12:51 Nicolas Saenz Julienne
2019-02-19 16:29 Nicolas Saenz Julienne
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