netdev - Re: [PATCH] USB host CDC Phonet network interface driver

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Date:	Fri, 24 Jul 2009 18:59:17 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Rémi Denis-Courmont" 
	<remi.denis-courmont@...ia.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	ext Dan Williams <dcbw@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] USB host CDC Phonet network interface driver

Am Freitag, 24. Juli 2009 16:19:41 schrieb Alan Cox:
> On Fri, 24 Jul 2009 16:12:41 +0200
>
> Oliver Neukum <oliver@...kum.org> wrote:
> > Am Freitag, 24. Juli 2009 14:48:05 schrieb Alan Cox:
> > > > No, I was thinking of having two full devices, a data channel and a
> > > > control channel for devices that really talk AT commands natively.
> > >
> > > If the hardware does it great, however for things like a 3G modem you
> > > have the problem that the PPP is over the AT command channel which may
> > > itself be multiplexed. And the muxing in question is *ugly* - sort of
> > > HDLC and LAP-B done wrong.
> >
> > Well, yes, but we would really like a separate control channel, so we
> > can query parameters like signal strength, while we do PPP over the data
> > channel.
>
> Thats the notion of the AT mux stuff - you get multiple AT channels and
> you can stuff PPP down one of them. It's still butt ugly.

That is a problem. But is it so ugly that we'd forgo the added functionality
rather than implement it in the kernel?
If not, I maintain that we should not maintain several different control channel
interfaces, like some devices use cdc-wdm, others a ttyUSB and the AT mux
stuff shall use yet a different method.

	Regards
		Oliver

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