isdn/gigaset: reset tty->receive_room when attaching ser_gigaset

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>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/isdn/gigaset/ser-gigaset.c b/drivers/isdn/gigaset/ser-gigaset.c
index 8c91fd5eb6fd..3ac9c4194814 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
          */