linux-kernel - Re: [PATCH/RFC 5/5] usb: Add support for streams alloc/dealloc to devio.c

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Message-Id: <201108170906.03901.hselasky@c2i.net>
Date:	Wed, 17 Aug 2011 09:06:03 +0200
From:	Hans Petter Selasky <hselasky@....net>
To:	"Amit Blay" <ablay@...eaurora.org>
Cc:	"Sarah Sharp" <sarah.a.sharp@...ux.intel.com>,
	"Tatyana Brokhman" <tlinder@...eaurora.org>, greg@...ah.com,
	linux-usb@...r.kernel.org, linux-arm-msm@...r.kernel.org,
	balbi@...com, "Amit Blay" <ablay@...lcomm.com>,
	"open list" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH/RFC 5/5] usb: Add support for streams alloc/dealloc to devio.c

On Wednesday 27 July 2011 08:21:35 Amit Blay wrote:
> Hi Sarah,
> 
> A gentle reminder, can you please take a look at the proposed solution
> below for stream alloc/dealloc in devio.c? I responded to your comments
> about the original patch.

Hi,

I'm looking into implementing USB 3.0 streams support for FreeBSD and would 
like to have a solution in Linux which is not too far apart, also regarding 
API's for userspace.

I would suggest overloading the "unsigned int pipe", instead of breaking 
existing API's by adding a new stream ID value. Also for LibUSB.

./linux/usb.h:  unsigned int pipe;              /* (in) pipe information */

As per definition there are 15 bits available for "pipe". I think it is not 
important to support more than 255 streams in the first go, hence I see no 
real applications that would benefit from that many streams yet.

#define usb_pipeendpoint(pipe)  (((pipe) >> 15) & 0xf)

Then I suggest a new function/IOCTL in libusb which can be used to switch 
on/off streams on a given endpoint. This is something which would need to be 
done before submitting any URB's on that endpoint. And would be similar to the 
clear-stall case.

If an URB is submitted on a stream when streams are disabled then it should 
just fail and vice versa.

--HPS
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