[PATCH 3/3] tty: n_gsm: add TIOCMIWAIT support

["D. Starke" <daniel.starke@siemens.com>]

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

Add support for the TIOCMIWAIT ioctl on the virtual ttys. This enables the
user to wait for virtual modem signals like RING.

Signed-off-by: Daniel Starke <daniel.starke@siemens.com>
---
 drivers/tty/n_gsm.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 118511c1fa37..48fb7dad44cd 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -1542,6 +1542,7 @@ static void gsm_process_modem(struct tty_struct *tty, struct gsm_dlci *dlci,
 	if (brk & 0x01)
 		tty_insert_flip_char(&dlci->port, 0, TTY_BREAK);
 	dlci->modem_rx = mlines;
+	wake_up_interruptible(&dlci->gsm->event);
 }
 
 /**
@@ -3848,6 +3849,35 @@ static int gsm_modem_update(struct gsm_dlci *dlci, u8 brk)
 	return -EPROTONOSUPPORT;
 }
 
+/**
+ * gsm_wait_modem_change	-	wait for modem status line change
+ * @dlci: channel
+ * @mask: modem status line bits
+ */
+
+static int gsm_wait_modem_change(struct gsm_dlci *dlci, u32 mask)
+{
+	struct gsm_mux *gsm = dlci->gsm;
+	u32 old = dlci->modem_rx & mask;
+	int ret;
+
+	if (gsm->dead)
+		return -ENODEV;
+
+	do {
+		ret = wait_event_interruptible(gsm->event, gsm->dead
+					      || old ^ (dlci->modem_rx & mask));
+		if (ret)
+			return ret;
+		if (dlci->state != DLCI_OPEN)
+			return -EL2NSYNC;
+		if (gsm->dead)
+			return -ENODEV;
+	} while ((old ^ (dlci->modem_rx & mask)) == 0);
+
+	return 0;
+}
+
 static bool gsm_carrier_raised(struct tty_port *port)
 {
 	struct gsm_dlci *dlci = container_of(port, struct gsm_dlci, port);
@@ -4107,6 +4137,8 @@ static int gsmtty_ioctl(struct tty_struct *tty,
 		gsm_destroy_network(dlci);
 		mutex_unlock(&dlci->mutex);
 		return 0;
+	case TIOCMIWAIT:
+		return gsm_wait_modem_change(dlci, arg);
 	default:
 		return -ENOIOCTLCMD;
 	}
-- 
2.34.1