n_gsm: wake up ldisc tty before using it

index 2c34c32..f887df6 100644
@@ -62,6 +62,7 @@
 #include <linux/netdevice.h>
 #include <linux/etherdevice.h>
 #include <linux/gsmmux.h>
+#include <linux/pm_runtime.h>
 
 static int debug;
 module_param(debug, int, 0600);

@@ -555,6 +556,27 @@ static int gsm_stuff_frame(const u8 *input, u8 *output, int len)
 	return olen;
 }
 
+static int pm_runtime_get_sync_tty(struct tty_struct *tty)
+{
+	int ret = 0;
+
+	/* Wakeup parent as tty itself doesn't enable runtime */
+	if (tty->dev->parent)
+		ret = pm_runtime_get_sync(tty->dev->parent);
+
+	return ret;
+}
+
+static int pm_runtime_put_tty(struct tty_struct *tty)
+{
+	int ret = 0;
+
+	if (tty->dev->parent)
+		ret = pm_runtime_put(tty->dev->parent);
+
+	return ret;
+}
+
 /**
  *	gsm_send	-	send a control frame
  *	@gsm: our GSM mux

@@ -1511,7 +1533,9 @@ static void gsm_dlci_begin_open(struct gsm_dlci *dlci)
 		return;
 	dlci->retries = gsm->n2;
 	dlci->state = DLCI_OPENING;
+	pm_runtime_get_sync_tty(gsm->tty);
 	gsm_command(dlci->gsm, dlci->addr, SABM|PF);
+	pm_runtime_put_tty(gsm->tty);
 	mod_timer(&dlci->t1, jiffies + gsm->t1 * HZ / 100);
 }
 

@@ -1533,7 +1557,9 @@ static void gsm_dlci_begin_close(struct gsm_dlci *dlci)
 		return;
 	dlci->retries = gsm->n2;
 	dlci->state = DLCI_CLOSING;
+	pm_runtime_get_sync_tty(gsm->tty);
 	gsm_command(dlci->gsm, dlci->addr, DISC|PF);
+	pm_runtime_put_tty(gsm->tty);
 	mod_timer(&dlci->t1, jiffies + gsm->t1 * HZ / 100);
 }
 

@@ -2286,7 +2312,9 @@ static void gsmld_receive_buf(struct tty_struct *tty, const unsigned char *cp,
 			flags = *f++;
 		switch (flags) {
 		case TTY_NORMAL:
+			pm_runtime_get_sync_tty(gsm->tty);
 			gsm->receive(gsm, *dp);
+			pm_runtime_put_tty(gsm->tty);
 			break;
 		case TTY_OVERRUN:
 		case TTY_BREAK:

@@ -2957,6 +2985,7 @@ static int gsmtty_open(struct tty_struct *tty, struct file *filp)
 {
 	struct gsm_dlci *dlci = tty->driver_data;
 	struct tty_port *port = &dlci->port;
+	int ret;
 
 	port->count++;
 	tty_port_tty_set(port, tty);

@@ -2968,7 +2997,11 @@ static int gsmtty_open(struct tty_struct *tty, struct file *filp)
 	/* Start sending off SABM messages */
 	gsm_dlci_begin_open(dlci);
 	/* And wait for virtual carrier */
-	return tty_port_block_til_ready(port, tty, filp);
+	pm_runtime_get_sync_tty(dlci->gsm->tty);
+	ret = tty_port_block_til_ready(port, tty, filp);
+	pm_runtime_put_tty(dlci->gsm->tty);
+
+	return ret;
 }
 
 static void gsmtty_close(struct tty_struct *tty, struct file *filp)

@@ -2986,11 +3019,14 @@ static void gsmtty_close(struct tty_struct *tty, struct file *filp)
 	gsm = dlci->gsm;
 	if (tty_port_close_start(&dlci->port, tty, filp) == 0)
 		return;
+	pm_runtime_get_sync_tty(gsm->tty);
 	gsm_dlci_begin_close(dlci);
 	if (test_bit(ASYNCB_INITIALIZED, &dlci->port.flags)) {
 		if (C_HUPCL(tty))
 			tty_port_lower_dtr_rts(&dlci->port);
 	}
+	pm_runtime_put_tty(gsm->tty);
+
 	tty_port_close_end(&dlci->port, tty);
 	tty_port_tty_set(&dlci->port, NULL);
 	return;

@@ -3012,10 +3048,12 @@ static int gsmtty_write(struct tty_struct *tty, const unsigned char *buf,
 	struct gsm_dlci *dlci = tty->driver_data;
 	if (dlci->state == DLCI_CLOSED)
 		return -EINVAL;
+	pm_runtime_get_sync_tty(dlci->gsm->tty);
 	/* Stuff the bytes into the fifo queue */
 	sent = kfifo_in_locked(dlci->fifo, buf, len, &dlci->lock);
 	/* Need to kick the channel */
 	gsm_dlci_data_kick(dlci);
+	pm_runtime_put_tty(dlci->gsm->tty);
 	return sent;
 }