[PATCH 7/8] tty: n_gsm: properly format Modem Status Command message

[Andrej Krpic <ak77@tnode.com>]

Change format of Modem Status Command (MSC) message that is
sent to the one expected in the receive function gsm_control_modem
and specified in 3GPP TS 27.010 version 12.0.0 Release 12, 5.4.6.3.7.

Wrongly formatted MSC causes DLC to be marked as constipated. A bug
appears after format of transmitted control messages is fixed and
control messages start to be recognized.

Signed-off-by: Andrej Krpic <ak77@tnode.com>
---
 drivers/tty/n_gsm.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 8aa90e0..b0d9edd 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -2874,12 +2874,11 @@ static int gsmtty_modem_update(struct gsm_dlci *dlci, u8 brk)
 	if (brk)
 		len++;
 
-	modembits[0] = len << 1 | EA;		/* Data bytes */
-	modembits[1] = dlci->addr << 2 | 3;	/* DLCI, EA, 1 */
-	modembits[2] = gsm_encode_modem(dlci) << 1 | EA;
+	modembits[0] = dlci->addr << 2 | 3;	/* DLCI, EA, 1 */
+	modembits[1] = gsm_encode_modem(dlci) << 1 | EA;
 	if (brk)
-		modembits[3] = brk << 4 | 2 | EA;	/* Valid, EA */
-	ctrl = gsm_control_send(dlci->gsm, CMD_MSC, modembits, len + 1);
+		modembits[2] = brk << 4 | 2 | EA;	/* Valid, EA */
+	ctrl = gsm_control_send(dlci->gsm, CMD_MSC, modembits, len);
 	if (ctrl == NULL)
 		return -ENOMEM;
 	return gsm_control_wait(dlci->gsm, ctrl);
-- 
2.7.0