linux-kernel - Re: duplicate requests on host side while streaming via uvcvideo gadget

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Message-ID: <ZcKk6QJXfGGo2DH9@pengutronix.de>
Date: Tue, 6 Feb 2024 22:30:17 +0100
From: Michael Grzeschik <mgr@...gutronix.de>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: duplicate requests on host side while streaming via uvcvideo
 gadget

On Tue, Feb 06, 2024 at 03:23:17AM +0000, Thinh Nguyen wrote:
>On Tue, Feb 06, 2024, Michael Grzeschik wrote:
>> Hi Thinh
>>
>> I found some strange situation while streaming via uvc-gadget to some
>> usb host. It happens when some requests are missed due to higher load on
>> the gadget machine. In some cases some requests will reach the host
>> twice. In my special case, I added the following changes [1] for the
>> host and gadget side.
>
>Does this only happen to some specific hosts?

>Are all the data of the duplicate requests matching or just some bits of
>the transfer? Were you able to confirm from some usb analyzer/sniffer
>that the data out the wire is actually duplicate?

Turns out, this duplicates are just misinterpretations.

The linux uvcvideo driver will parse the uvc header payload twice. (If
the FID was incremented inbetween). This led to those double misleading
outputs. Although this means that there is a bug in
uvc_video_stats_decode for incrementing the error count.

Anyway, so just ignore this whole thread and be thanked for even having any
thoghts on this.

Regards,
Michael

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