[PATCH] USB: serial: ftdi_sio: Fix serial port stall after resume

[Helge Deller <deller@xxxxxx>]

With a 4-port serial USB HUB with FT232BM chips the serial ports stop
working after a software suspend/resume cycle.
Rewriting the latency timer during the resume phase fixes it.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Helge Deller <deller@xxxxxx>

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 9823bb424abd..8ee6cf6215c1 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1092,6 +1092,7 @@ static u32 ftdi_232bm_baud_base_to_divisor(int baud, int base);
 static u32 ftdi_232bm_baud_to_divisor(int baud);
 static u32 ftdi_2232h_baud_base_to_divisor(int baud, int base);
 static u32 ftdi_2232h_baud_to_divisor(int baud);
+static int ftdi_reset_resume(struct usb_serial *serial);

 static struct usb_serial_driver ftdi_sio_device = {
 	.driver = {
@@ -1122,6 +1123,7 @@ static struct usb_serial_driver ftdi_sio_device = {
 	.set_termios =		ftdi_set_termios,
 	.break_ctl =		ftdi_break_ctl,
 	.tx_empty =		ftdi_tx_empty,
+	.reset_resume =		ftdi_reset_resume,
 };

 static struct usb_serial_driver * const serial_drivers[] = {
@@ -2379,6 +2381,16 @@ static int ftdi_stmclite_probe(struct usb_serial *serial)
 	return 0;
 }

+static int ftdi_reset_resume(struct usb_serial *serial)
+{
+	struct usb_serial_port *port = serial->port[0];
+
+	if (tty_port_initialized(&port->port))
+		write_latency_timer(port);
+
+	return usb_serial_generic_resume(serial);
+}
+
 static int ftdi_sio_port_remove(struct usb_serial_port *port)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);