[PATCH] USB: serial: ftdi_sio: Fix GPIO not working in autosuspend

[Karoly Pados <pados@pados.hu>]

There is a bug in the current GPIO code for ftdi_sio: it failed to take USB
autosuspend into account. If the device is in autosuspend, calls to
usb_control_msg() fail with -EHOSTUNREACH. Because the standard value for
autosuspend timeout is usually 2-5 seconds, this made it almost impossible
to use the GPIOs on machines that have USB autosuspend enabled. This patch
fixes the issue by acquiring a PM lock on the device for the duration of
the USB transfers. Tested on an FT231X device.

Signed-off-by: Karoly Pados <pados@pados.hu>
---
Please consider backporting to 4.20.x, otherwise the GPIO driver is not
really usable for anybody with USB autosuspend enabled (eg. many laptops),
at least not without manual configuration.

 drivers/usb/serial/ftdi_sio.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 1ab2a6191013..01813dce37f2 100644
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1783,6 +1783,13 @@ static int ftdi_set_bitmode(struct usb_serial_port *port, u8 mode)
 	int result;
 	u16 val;
 
+	result = usb_autopm_get_interface(port->serial->interface);
+	if (result) {
+		dev_err(&port->serial->interface->dev,
+			"Failed to wake device from autosuspend.\n");
+		return result;
+	}
+
 	val = (mode << 8) | (priv->gpio_output << 4) | priv->gpio_value;
 	result = usb_control_msg(serial->dev,
 				 usb_sndctrlpipe(serial->dev, 0),
@@ -1795,6 +1802,8 @@ static int ftdi_set_bitmode(struct usb_serial_port *port, u8 mode)
 			val, result);
 	}
 
+	usb_autopm_put_interface(port->serial->interface);
+
 	return result;
 }
 
@@ -1846,9 +1855,18 @@ static int ftdi_read_cbus_pins(struct usb_serial_port *port)
 	unsigned char *buf;
 	int result;
 
+	result = usb_autopm_get_interface(port->serial->interface);
+	if (result) {
+		dev_err(&port->serial->interface->dev,
+			"Failed to wake device from autosuspend.\n");
+		return result;
+	}
+
 	buf = kmalloc(1, GFP_KERNEL);
-	if (!buf)
+	if (!buf) {
+		usb_autopm_put_interface(port->serial->interface);
 		return -ENOMEM;
+	}
 
 	result = usb_control_msg(serial->dev,
 				 usb_rcvctrlpipe(serial->dev, 0),
@@ -1863,6 +1881,7 @@ static int ftdi_read_cbus_pins(struct usb_serial_port *port)
 	}
 
 	kfree(buf);
+	usb_autopm_put_interface(port->serial->interface);
 
 	return result;
 }
-- 
2.20.1