Make sure to log an error on short transfers when reading a device
register.

Also clear the provided buffer (which if often an uninitialised
automatic variable) on errors as the driver currently does not bother to
check for errors.

Signed-off-by: Johan Hovold <[email protected]>
---
 drivers/usb/serial/mos7720.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/serial/mos7720.c b/drivers/usb/serial/mos7720.c
index 91bc170b408a..acf431e02699 100644
--- a/drivers/usb/serial/mos7720.c
+++ b/drivers/usb/serial/mos7720.c
@@ -234,11 +234,16 @@ static int read_mos_reg(struct usb_serial *serial, 
unsigned int serial_portnum,
 
        status = usb_control_msg(usbdev, pipe, request, requesttype, value,
                                     index, buf, 1, MOS_WDR_TIMEOUT);
-       if (status == 1)
+       if (status == 1) {
                *data = *buf;
-       else if (status < 0)
+       } else {
                dev_err(&usbdev->dev,
                        "mos7720: usb_control_msg() failed: %d\n", status);
+               if (status >= 0)
+                       status = -EIO;
+               *data = 0;
+       }
+
        kfree(buf);
 
        return status;
-- 
2.10.2

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