[PATCH 5.15 123/230] tty: n_gsm: fix missing update of modem controls after DLCI open

Greg Kroah-Hartman
2022-07-11T09:51:38Z

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

[ Upstream commit 48473802506d2d6151f59e0e764932b33b53cb3b ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/n_gsm.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index d3d5308daf35..c52d5e0d5c6f 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -371,6 +371,7 @@ 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
@@ -1489,6 +1490,9 @@ static void gsm_dlci_open(struct gsm_dlci *dlci)
dlci->state = DLCI_OPEN;
if (debug & 8)
pr_debug("DLCI %d goes open.\n", dlci->addr);
+ /* Send current modem state */
+ if (dlci->addr)
+ gsmtty_modem_update(dlci, 0);
wake_up(&dlci->gsm->event);
}

--
2.35.1