USB: serial: ftdi_sio: fix GPIO not working in autosuspend

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>
[ johan: simplify code somewhat ]
Fixes: ba93cc7da896 ("USB: serial: ftdi_sio: implement GPIO support for FT-X devices")
Cc: stable <stable@vger.kernel.org>	# 4.20
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/ftdi_sio.c b/drivers/usb/serial/ftdi_sio.c
index 1ab2a61..77ef4c4 100644 (file)
--- a/drivers/usb/serial/ftdi_sio.c
+++ b/drivers/usb/serial/ftdi_sio.c
@@ -1783,6 +1783,10 @@ static int ftdi_set_bitmode(struct usb_serial_port *port, u8 mode)
        int result;
        u16 val;
 
+       result = usb_autopm_get_interface(serial->interface);
+       if (result)
+               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 +1799,8 @@ static int ftdi_set_bitmode(struct usb_serial_port *port, u8 mode)
                        val, result);
        }
 
+       usb_autopm_put_interface(serial->interface);
+
        return result;
 }
 
@@ -1846,9 +1852,15 @@ static int ftdi_read_cbus_pins(struct usb_serial_port *port)
        unsigned char *buf;
        int result;
 
+       result = usb_autopm_get_interface(serial->interface);
+       if (result)
+               return result;
+
        buf = kmalloc(1, GFP_KERNEL);
-       if (!buf)
+       if (!buf) {
+               usb_autopm_put_interface(serial->interface);
                return -ENOMEM;
+       }
 
        result = usb_control_msg(serial->dev,
                                 usb_rcvctrlpipe(serial->dev, 0),
@@ -1863,6 +1875,7 @@ static int ftdi_read_cbus_pins(struct usb_serial_port *port)
        }
 
        kfree(buf);
+       usb_autopm_put_interface(serial->interface);
 
        return result;
 }