From 48473802506d2d6151f59e0e764932b33b53cb3b Mon Sep 17 00:00:00 2001
From: Daniel Starke <daniel.starke@siemens.com>
Date: Wed, 20 Apr 2022 03:13:44 -0700
Subject: [PATCH] tty: n_gsm: fix missing update of modem controls after DLCI open
Git-commit: 48473802506d2d6151f59e0e764932b33b53cb3b
Patch-mainline: v5.18-rc5
References: git-fixes

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>
Link: https://lore.kernel.org/r/20220420101346.3315-1-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 drivers/tty/n_gsm.c |    4 ++++
 1 file changed, 4 insertions(+)

--- 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
@@ -1483,6 +1484,9 @@ static void gsm_dlci_open(struct gsm_dlc
 		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);
 }