From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752072AbbGMXOq (ORCPT ); Mon, 13 Jul 2015 19:14:46 -0400 Received: from mail-qk0-f180.google.com ([209.85.220.180]:36590 "EHLO mail-qk0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751117AbbGMXOp (ORCPT ); Mon, 13 Jul 2015 19:14:45 -0400 Message-ID: <55A44662.4080706@hurleysoftware.com> Date: Mon, 13 Jul 2015 19:14:42 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Tilman Schmidt , Paul Bolle CC: netdev@vger.kernel.org, David Miller , Hansjoerg Lipp , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] isdn/gigaset: reset tty->receive_room when attaching ser_gigaset References: In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/13/2015 06:37 PM, Tilman Schmidt wrote: > Commit 79901317ce80 ("n_tty: Don't flush buffer when closing ldisc"), > first merged in kernel release 3.10, caused the following regression > in the Gigaset M101 driver: > > Before that commit, when closing the N_TTY line discipline in > preparation to switching to N_GIGASET_M101, receive_room would be > reset to a non-zero value by the call to n_tty_flush_buffer() in > n_tty's close method. With the removal of that call, receive_room > might be left at zero, blocking data reception on the serial line. That commit didn't cause the problem; it was a bug all along. For example, if the tty had first been hooked up to some other line discipline which consumed most of tty->receive_room, _then_ switched to N_GIGASET_M101 line discipline, the same problem would have occurred. Non-flow controlling line disciplines _must_ set tty->receive_room on line discipline open because they are declaring that every input they can accept that much data. Regards, Peter Hurley > The present patch fixes that regression by setting receive_room > to an appropriate value in the ldisc open method. > > Fixes: 79901317ce80 ("n_tty: Don't flush buffer when closing ldisc") > Signed-off-by: Tilman Schmidt > --- > drivers/isdn/gigaset/ser-gigaset.c | 11 ++++++++++- > 1 files changed, 10 insertions(+), 1 deletions(-) > > diff --git a/drivers/isdn/gigaset/ser-gigaset.c b/drivers/isdn/gigaset/ser-gigaset.c > index 8c91fd5..3ac9c41 100644 > --- a/drivers/isdn/gigaset/ser-gigaset.c > +++ b/drivers/isdn/gigaset/ser-gigaset.c > @@ -524,9 +524,18 @@ gigaset_tty_open(struct tty_struct *tty) > cs->hw.ser->tty = tty; > atomic_set(&cs->hw.ser->refcnt, 1); > init_completion(&cs->hw.ser->dead_cmp); > - > tty->disc_data = cs; > > + /* Set the amount of data we're willing to receive per call > + * from the hardware driver to half of the input buffer size > + * to leave some reserve. > + * Note: We don't do flow control towards the hardware driver. > + * If more data is received than will fit into the input buffer, > + * it will be dropped and an error will be logged. This should > + * never happen as the device is slow and the buffer size ample. > + */ > + tty->receive_room = RBUFSIZE/2; > + > /* OK.. Initialization of the datastructures and the HW is done.. Now > * startup system and notify the LL that we are ready to run > */ >