[PATCH 5.4 142/314] tty: n_gsm: Fix waking up upper tty layer when room available

[Greg Kroah-Hartman]

From: Gregory CLEMENT <gregory.clem...@bootlin.com>

[ 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.clem...@bootlin.com>
Link: 
https://lore.kernel.org/r/20200512115323.1447922-4-gregory.clem...@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 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 a5165f989fcf6..8a0d66a05af59 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:
@@ -2519,7 +2537,7 @@ 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