Date: Fri, 4 Mar 2011 15:02:05 +0000
From: Alan Cox <alan@linux.intel.com>
To: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Ken Mills <ken.k.mills@intel.com>, Greg Kroah-Hartman <gregkh@suse.de>,
        linux-kernel@vger.kernel.org
Subject: Re: Usage of the n_gsm line discipline
Message-ID: <20110304150205.7805f406@bob.linux.org.uk>
In-Reply-To: <20110304152348.5d03c8ef@surf>
References: <20110304152348.5d03c8ef@surf>
Organization: Intel
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> So, maybe I misconfigured n_gsm, or I didn't understand how to use it.
> Would it be possible to have a few details on how it is supposed to be
> used ? I haven't been able to find any userspace code that currently
> makes use of n_gsm. Is it available somewhere ?

Check dmesg but if your modem doesn't start up in multiplex mode you
will need to issue an AT+CMUX command first. So the usual sequence is

	write AT+CMUXblah [see GSM spec/modem command info]
	TIOCSETD
	GSMIOC_GETCONF
		[modify anything needed]
	GSMIOC_SETCONF

The defaults uses are the T1/T2/N2 from the spec, we are not the
initiator, and using encoding 1 (ie HDLC/LAP like), 64byte MRU/MTU.

So at the very least you'll want to set initiator to 1 so that we start
issuing SABM messages at the modem to enter mux mode.

> If I can get it to work, I am willing to contribute a
> Documentation/n_gsm.txt document.

That would be good.

Alan
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