isdn/gigaset: unclog bas_gigaset AT response pipe

Recover from a lost HD_RECEIVEATDATA_ACK message by sending a
zero-length HD_READ_ATMESSAGE command when ev_layer sends "+++".

Signed-off-by: Tilman Schmidt <tilman@imap.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 22 insertions, 0 deletions

diff --git a/drivers/isdn/gigaset/bas-gigaset.c b/drivers/isdn/gigaset/bas-gigaset.c
index 7520bc6f387..540f6d0bb75 100644
--- a/drivers/isdn/gigaset/bas-gigaset.c
+++ b/drivers/isdn/gigaset/bas-gigaset.c
@@ -1896,6 +1896,28 @@ static int gigaset_write_cmd(struct cardstate *cs, struct cmdbuf_t *cb)
          * The next command will reopen the AT channel automatically.
          */
         if (cb->len == 3 && !memcmp(cb->buf, "+++", 3)) {
+                /* If an HD_RECEIVEATDATA_ACK message remains unhandled
+                 * because of an error, the base never sends another one.
+                 * The response channel is thus effectively blocked.
+                 * Closing and reopening the AT channel does *not* clear
+                 * this condition.
+                 * As a stopgap measure, submit a zero-length AT read
+                 * before closing the AT channel. This has the undocumented
+                 * effect of triggering a new HD_RECEIVEATDATA_ACK message
+                 * from the base if necessary.
+                 * The subsequent AT channel close then discards any pending
+                 * messages.
+                 */
+                spin_lock_irqsave(&cs->lock, flags);
+                if (!(cs->hw.bas->basstate & BS_ATRDPEND)) {
+                        kfree(cs->hw.bas->rcvbuf);
+                        cs->hw.bas->rcvbuf = NULL;
+                        cs->hw.bas->rcvbuf_size = 0;
+                        cs->hw.bas->retry_cmd_in = 0;
+                        atread_submit(cs, 0);
+                }
+                spin_unlock_irqrestore(&cs->lock, flags);
+
                 rc = req_submit(cs->bcs, HD_CLOSE_ATCHANNEL, 0, BAS_TIMEOUT);
                 if (cb->wake_tasklet)
                         tasklet_schedule(cb->wake_tasklet);