From: Peter Hurley <peter@hurleysoftware.com>
To: Tilman Schmidt <tilman@imap.cc>, Paul Bolle <pebolle@tiscali.nl>
Cc: netdev@vger.kernel.org, David Miller <davem@davemloft.net>,
Hansjoerg Lipp <hjlipp@web.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] isdn/gigaset: reset tty->receive_room when attaching ser_gigaset
Date: Mon, 13 Jul 2015 19:14:42 -0400 [thread overview]
Message-ID: <55A44662.4080706@hurleysoftware.com> (raw)
In-Reply-To: <ff18ec15ffc6347cd5574a66eb67cc9483361afa.1436826434.git.tilman@imap.cc>
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 <tilman@imap.cc>
> ---
> 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
> */
>
next prev parent reply other threads:[~2015-07-13 23:14 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-13 22:37 [PATCH 0/2] Fix long-standing regression in ser_gigaset ISDN driver Tilman Schmidt
2015-07-13 22:37 ` [PATCH 1/2] isdn/gigaset: reset tty->receive_room when attaching ser_gigaset Tilman Schmidt
2015-07-13 23:14 ` Peter Hurley [this message]
2015-07-13 23:58 ` Tilman Schmidt
2015-07-14 19:01 ` Paul Bolle
2015-07-14 12:50 ` Sergei Shtylyov
2015-07-13 22:37 ` [PATCH 2/2] isdn/gigaset: drop unused ldisc methods Tilman Schmidt
2015-07-14 19:03 ` Paul Bolle
2015-07-16 0:25 ` [PATCH 0/2] Fix long-standing regression in ser_gigaset ISDN driver David Miller
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