[PATCH v3 1/3] tty: n_gsm: fix missing update of modem controls after DLCI open

["D. Starke" <daniel.starke@siemens.com>]

From: Daniel Starke <daniel.starke@siemens.com>

Currently the peer is not informed about the initial state of the modem
control lines after a new DLCI has been opened.
Fix this by sending the initial modem control line states after DLCI open.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
---
 drivers/tty/n_gsm.c | 4 ++++
 1 file changed, 4 insertions(+)

All remarks have been incorporated.
Compared to the original patch the additional comment on the prototypes was
removed and the comment in gsm_dlci_open() was moved to a separate line.
The commit message remains unchanged.
This is version 3 of the patch because the second version was missing the
change remarks.

Link: https://lore.kernel.org/all/YlkQ5Jh8HIm+AJHe@kroah.com/

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index f3fb66be8513..07d03447cdfd 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -370,6 +370,7 @@ static const u8 gsm_fcs8[256] = {
 #define GOOD_FCS	0xCF
 
 static int gsmld_output(struct gsm_mux *gsm, u8 *data, int len);
+static int gsmtty_modem_update(struct gsm_dlci *dlci, u8 brk);
 
 /**
  *	gsm_fcs_add	-	update FCS
@@ -1479,6 +1480,9 @@ static void gsm_dlci_open(struct gsm_dlci *dlci)
 		pr_debug("DLCI %d goes open.\n", dlci->addr);
 	/* Register gsmtty driver,report gsmtty dev add uevent for user */
 	tty_register_device(gsm_tty_driver, dlci->addr, NULL);
+	/* Send current modem state */
+	if (dlci->addr)
+		gsmtty_modem_update(dlci, 0);
 	wake_up(&dlci->gsm->event);
 }
 
-- 
2.25.1