Subject: Re: [PATCH 1/2] isdn/gigaset: reset tty->receive_room when attaching ser_gigaset

From: Sergei Shtylyov <[email-masked]>
Date: Tue, 14 Jul 2015 15:50:32 +0300

Hello.

On 7/14/2015 1:37 AM, 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.

> 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 <[email-masked]>
> ---
>   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);
> -

    Unrelated change?

>   	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;

    The general kernel coding style is to surround operators with spaces.

[...]

MBR, Sergei