linux-kernel - Re: [PATCH 1/2] drivers:staging:ti-st: move TI

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Date:	Fri, 08 Oct 2010 10:32:26 +0200
From:	Marcel Holtmann <marcel@...tmann.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"Savoy, Pavan" <pavan_savoy@...com>,
	Jiri Slaby <jirislaby@...il.com>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH 1/2] drivers:staging:ti-st: move TI_ST from staging

Hi Alan,

> > ldisc is the ONLY way to do it, isn't it? Do I have any other option?
> 
> Userspace but even then it wouldn't solve your problem
> 
> > The situation was something similar here.
> > What I was trying to get to is how we can have a per-device context if a driver is just a line discipline driver?
> 
> tty->driver_data
> 		TTY private data
> tty->disc_data
> 		LDISC per instance private data
> 
> So when your ldisc is opened attach your data to the tty->disc_data, and
> when it is closed free the data.
> 
> > I have 3 sub-devices if you will on a device which is interfaced over UART,
> > One of them is Bluetooth which requires any UART Bluetooth device to have its
> > Own line discipline - N_HCI.
> 
> The problem is that your chip by the sound of it does not talk the
> bluetooth ldisc - it talks something more complex.
> 
> The obvious question then is
> 
> Does it talk
> 
> 1.	HCI with bits nailed on
> 2.	Something rather different which contains muxed data some of
> which is reformatted up to create HCI
> 
> In the first case it may be worth seeing if the existing N_HCI could
> support forwarding unknown frame types to a helper. In the latter it's a
> lot trickier. It is possible to create a mux tty layer (see n_gsm.c) but
> that is almost certainly overkill for this.
> 
> I wonder what Marcel thinks in terms of re-using the bluetooth ldisc ?

If you get a sane proposal, then yes, N_HCI could act as multiplexer and
forward certain frame types.

This all depends on how clear the separation is. If you expect to send
HCI commands from these "clients" then there is a problem with the
Bluetooth subsystem and its enforced flow control. You don't wanna mess
with that since it has side effects. And I am not giving outside drivers
real control over. The Bluetooth drivers have to stay dumb transport
drivers without any Bluetooth core logic.

So can you give me a few quick hints on what you would need to forward
actually.

Regards

Marcel


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