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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Daniel Starke <daniel.starke@siemens.com>
Subject: [PATCH 5.15 131/139] tty: n_gsm: fix wrong tty control line for flow control
Date:   Mon, 28 Feb 2022 18:25:05 +0100
Message-Id: <20220228172401.455830521@linuxfoundation.org>
In-Reply-To: <20220228172347.614588246@linuxfoundation.org>
References: <20220228172347.614588246@linuxfoundation.org>
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From: daniel.starke@siemens.com <daniel.starke@siemens.com>

commit c19d93542a6081577e6da9bf5e887979c72e80c1 upstream.

tty flow control is handled via gsmtty_throttle() and gsmtty_unthrottle().
Both functions propagate the outgoing hardware flow control state to the
remote side via MSC (modem status command) frames. The local state is taken
from the RTS (ready to send) flag of the tty. However, RTS gets mapped to
DTR (data terminal ready), which is wrong.
This patch corrects this by mapping RTS to RTS.

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/20220218073123.2121-5-daniel.starke@siemens.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/n_gsm.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -3180,9 +3180,9 @@ static void gsmtty_throttle(struct tty_s
 	if (dlci->state == DLCI_CLOSED)
 		return;
 	if (C_CRTSCTS(tty))
-		dlci->modem_tx &= ~TIOCM_DTR;
+		dlci->modem_tx &= ~TIOCM_RTS;
 	dlci->throttled = true;
-	/* Send an MSC with DTR cleared */
+	/* Send an MSC with RTS cleared */
 	gsmtty_modem_update(dlci, 0);
 }
 
@@ -3192,9 +3192,9 @@ static void gsmtty_unthrottle(struct tty
 	if (dlci->state == DLCI_CLOSED)
 		return;
 	if (C_CRTSCTS(tty))
-		dlci->modem_tx |= TIOCM_DTR;
+		dlci->modem_tx |= TIOCM_RTS;
 	dlci->throttled = false;
-	/* Send an MSC with DTR set */
+	/* Send an MSC with RTS set */
 	gsmtty_modem_update(dlci, 0);
 }