From: Sascha Hauer <s.hauer@pengutronix.de>
To: Alan Cox <gnomes@lxorguk.ukuu.org.uk>
Cc: linux-kernel@vger.kernel.org,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
kernel@pengutronix.de
Subject: Re: tty: n_gsm: fix closing multiplexer mode
Date: Tue, 23 May 2017 09:55:21 +0200 [thread overview]
Message-ID: <20170523075521.asva3wqq7vb2pnhp@pengutronix.de> (raw)
In-Reply-To: <20170522191617.35dd508f@alans-desktop>
On Mon, May 22, 2017 at 07:16:17PM +0100, Alan Cox wrote:
> > disconnect frame before initialising multiplex mode. Since it's not so
> > nice that userspace has to know the layout of a disconnect frame,
> > the second patch introduces a disconnect ioctl which can be issued
> > right before closing the physical port during the first session.
> > This ioctl is only useful when during the second session it is known
> > the the first session has been closed properly, so I'm not sure
> > how useful it is to introduce such an ioctl.
>
> I don't think it justifies an ioctl and the likely use case is that the
> tty is hung up when the process dies so would already be in N_TTY at the
> point anyone tried to clean up.
Ok, so let's drop the second patch.
>
> A more interesting question - and I don't have enough hardware to test
> this any more - would be whether we can safely send that sequence if our
> initial connects failed a few times so we try disconnect/reconnect.
In my current userspace test program I now unconditionally send the
sequence right before sending the AT+CMUX command. This works fine, no
matter if the modem was still in CMUX mode or not. I can only speak for
a UBLOX modem though, other modems might behave differently here. For
example my UBLOX needs the CLD message to close down the multiplexer,
just closing DLC0 does not work.
Sascha
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prev parent reply other threads:[~2017-05-23 7:55 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-22 8:14 tty: n_gsm: fix closing multiplexer mode Sascha Hauer
2017-05-22 8:14 ` [PATCH 1/2] tty: n_gsm: do not send/receive in ldisc close path Sascha Hauer
2017-05-22 8:15 ` [PATCH 2/2] tty: n_gsm: Add GSMIOC_DISCONNECT ioctl to disconnect the multiplexer Sascha Hauer
2017-05-22 9:25 ` Greg Kroah-Hartman
2017-05-22 9:29 ` Sascha Hauer
2017-05-22 18:16 ` tty: n_gsm: fix closing multiplexer mode Alan Cox
2017-05-23 7:55 ` Sascha Hauer [this message]
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