linux-kernel - Re: [Patch] Increase USBFS Bulk Transfer size

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Date:	Sun, 16 Oct 2011 11:10:09 +0200
From:	Johannes Stezenbach <js@...21.net>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Markus Rechberger <mrechberger@...il.com>,
	Greg KH <gregkh@...e.de>, USB list <linux-usb@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Patch] Increase USBFS Bulk Transfer size

On Sat, Oct 15, 2011 at 03:04:28PM -0400, Alan Stern wrote:
> On Sat, 15 Oct 2011, Johannes Stezenbach wrote:
> 
> > What I meant to say is Markus' statement that the device only
> > works at a certain transfer size cannot be true since
> > this size is not visible to the device via the USB bus.
> 
> That's what I would expect, too.  But did you take a look at the usbmon 
> traces Markus acquired?
> 
> 	http://marc.info/?l=linux-usb&m=131845614819045&w=2

I glanced at them for 3 seconds, but I cannot be bothered
to analyze them in detail.  The ASCII usbmon traces don't
show full USB packet contents anyway so you can't see if
partial MPEG TS packets are missing.

> They aren't completely definitive because the communications between
> the computer and the device _before_ the bulk transfers started were
> different.  However they do clearly show the device working with
> 24064-byte transfers and not working with 12288+11776-byte transfers.

The device transfers data in the "not working" case, it's just that
the MPEG TS sync byte is not where Markus expects it, which could
be explained by a partial MPEG TS packet left in the device's FIFO
from previous interaction.


Johannes
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