From:   "D. Starke" <daniel.starke@siemens.com>
To:     linux-serial@vger.kernel.org, gregkh@linuxfoundation.org,
        jirislaby@kernel.org, ilpo.jarvinen@linux.intel.com
Cc:     linux-kernel@vger.kernel.org,
        Daniel Starke <daniel.starke@siemens.com>
Subject: [PATCH v2 2/3] tty: n_gsm: add RING/CD control support
Date:   Thu,  2 Feb 2023 15:59:33 +0100
Message-Id: <20230202145934.22641-2-daniel.starke@siemens.com>
In-Reply-To: <20230202145934.22641-1-daniel.starke@siemens.com>
References: <20230202145934.22641-1-daniel.starke@siemens.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Feedback-ID: 519:519-314044:519-21489:flowmailer
Precedence: bulk

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

The status lines ring and carrier detect are used by the modem to signal
incoming calls (RING) or an established connection (CD). This is
implemented as physical lines on a standard RS232 connection. However,
the muxer protocol encodes these status lines as modem bits IC and DV.
These incoming lines are masked by tty driver (see tty_io.c) and cannot be
set by a user application.

Allow setting RING via TIOCM_OUT1 and CD via TIOCM_OUT2 to allow
implementation of a modem or modem emulator.

Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
---
 drivers/tty/n_gsm.c | 5 +++++
 1 file changed, 5 insertions(+)

v1 -> v2:
No changes.

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index d068df1cf2fd..cf1ab7d619d9 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -546,6 +546,11 @@ static u8 gsm_encode_modem(const struct gsm_dlci *dlci)
 		modembits |= MDM_IC;
 	if (dlci->modem_tx & TIOCM_CD || dlci->gsm->initiator)
 		modembits |= MDM_DV;
+	/* special mappings for passive side to operate as UE */
+	if (dlci->modem_tx & TIOCM_OUT1)
+		modembits |= MDM_IC;
+	if (dlci->modem_tx & TIOCM_OUT2)
+		modembits |= MDM_DV;
 	return modembits;
 }
 
-- 
2.34.1