[PATCH AUTOSEL 4.19 090/172] tty: n_gsm: Fix waking up upper tty layer when room available

[Sasha Levin <sashal@xxxxxxxxxx>]

From: Gregory CLEMENT <gregory.clement@xxxxxxxxxxx>

[ Upstream commit 01dbb362f0a114fbce19c8abe4cd6f4710e934d5 ]

Warn the upper layer when n_gms is ready to receive data
again. Without this the associated virtual tty remains blocked
indefinitely.

Fixes: e1eaea46bb40 ("tty: n_gsm line discipline")
Signed-off-by: Gregory CLEMENT <gregory.clement@xxxxxxxxxxx>
Link: https://lore.kernel.org/r/20200512115323.1447922-4-gregory.clement@xxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/tty/n_gsm.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/n_gsm.c b/drivers/tty/n_gsm.c
index 8d8229dd2796..166052002b79 100644
--- a/drivers/tty/n_gsm.c
+++ b/drivers/tty/n_gsm.c
@@ -665,7 +665,7 @@ static struct gsm_msg *gsm_data_alloc(struct gsm_mux *gsm, u8 addr, int len,
  *	FIXME: lock against link layer control transmissions
  */
 
-static void gsm_data_kick(struct gsm_mux *gsm)
+static void gsm_data_kick(struct gsm_mux *gsm, struct gsm_dlci *dlci)
 {
 	struct gsm_msg *msg, *nmsg;
 	int len;
@@ -697,6 +697,24 @@ static void gsm_data_kick(struct gsm_mux *gsm)
 
 		list_del(&msg->list);
 		kfree(msg);
+
+		if (dlci) {
+			tty_port_tty_wakeup(&dlci->port);
+		} else {
+			int i = 0;
+
+			for (i = 0; i < NUM_DLCI; i++) {
+				struct gsm_dlci *dlci;
+
+				dlci = gsm->dlci[i];
+				if (dlci == NULL) {
+					i++;
+					continue;
+				}
+
+				tty_port_tty_wakeup(&dlci->port);
+			}
+		}
 	}
 }
 
@@ -748,7 +766,7 @@ static void __gsm_data_queue(struct gsm_dlci *dlci, struct gsm_msg *msg)
 	/* Add to the actual output queue */
 	list_add_tail(&msg->list, &gsm->tx_list);
 	gsm->tx_bytes += msg->len;
-	gsm_data_kick(gsm);
+	gsm_data_kick(gsm, dlci);
 }
 
 /**
@@ -1209,7 +1227,7 @@ static void gsm_control_message(struct gsm_mux *gsm, unsigned int command,
 		gsm_control_reply(gsm, CMD_FCON, NULL, 0);
 		/* Kick the link in case it is idling */
 		spin_lock_irqsave(&gsm->tx_lock, flags);
-		gsm_data_kick(gsm);
+		gsm_data_kick(gsm, NULL);
 		spin_unlock_irqrestore(&gsm->tx_lock, flags);
 		break;
 	case CMD_FCOFF:
@@ -2406,7 +2424,7 @@ static void gsmld_write_wakeup(struct tty_struct *tty)
 	/* Queue poll */
 	clear_bit(TTY_DO_WRITE_WAKEUP, &tty->flags);
 	spin_lock_irqsave(&gsm->tx_lock, flags);
-	gsm_data_kick(gsm);
+	gsm_data_kick(gsm, NULL);
 	if (gsm->tx_bytes < TX_THRESH_LO) {
 		gsm_dlci_data_sweep(gsm);
 	}
-- 
2.25.1