The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

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

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

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c index e440c7f6d20e..979dc9151383 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 @@ -1483,6 +1484,9 @@ 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); }