From: Oliver Neukum <oliver@neukum.org>
Organization: Novell
To: Andrew Morton <akpm@linux-foundation.org>
Subject: Re: System hang (and other problems) with cdc_acm
Date: Mon, 26 Jan 2009 09:36:00 +0100
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Cc: "Thomas Tuttle" <linux-kernel@ttuttle.net>, linux-kernel@vger.kernel.org,
       linux-usb@vger.kernel.org
References: <e4cb19870901191220y622e0120m512596656c72bbf3@mail.gmail.com> <20090125232753.db40c160.akpm@linux-foundation.org>
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Am Monday 26 January 2009 08:27:53 schrieb Andrew Morton:
> > I've got a Lenovo X200 with an Ericsson F3507g Mobile Broadband Module
> > (a 3G cellular data card with built-in GPS), which uses the cdc_acm
> > driver. ?I've experienced a couple of problems with it. ?First, it
> > tends to hang the system after I've been using it for a while. ?This
> > occurs whenever it's sending a lot of data to/from the computer,
> > whether it's a PPP connection or a GPS data stream. ?I'm not sure how
> > to debug this; the Caps Lock light isn't flashing, so I'm not sure if
> > it's a panic or just a hang. ?Second, if I read one of the TTYs using
> > "cat", I get a ton of blank lines. ?To make any sense of the data
> > stream, I have to do cat /dev/ttyACM0 | grep -v "^$".
> > 
> > If anyone could help me debug this, I'd be greatly appreciative.

It is probably necessary to setup a watchdog. Can you do that?
As for the blank lines, I am not sure this is a bug. Your device may
indeed send a lot of newlines.

	Regards
		Oliver

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