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>
diff --git a/drivers/isdn/gigaset/bas-gigaset.c b/drivers/isdn/gigaset/bas-gigaset.c
index 7520bc6..540f6d0 100644
--- a/drivers/isdn/gigaset/bas-gigaset.c
+++ b/drivers/isdn/gigaset/bas-gigaset.c
@@ -1896,6 +1896,28 @@
* 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);
