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    Subject[PATCH 3.2 108/126] isdn/gigaset: reset tty->receive_room when attaching ser_gigaset
    3.2.85-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Tilman Schmidt <tilman@imap.cc>

    commit fd98e9419d8d622a4de91f76b306af6aa627aa9c upstream.

    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 <tilman@imap.cc>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/isdn/gigaset/ser-gigaset.c | 11 ++++++++++-
    1 file changed, 10 insertions(+), 1 deletion(-)

    --- a/drivers/isdn/gigaset/ser-gigaset.c
    +++ b/drivers/isdn/gigaset/ser-gigaset.c
    @@ -526,9 +526,18 @@ 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
    */
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