[PATCH v3] USB: serial: cp210x.c -fix partnum regression for devices not having a part number

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When adding GPIO support for the cp2105, the mentioned commit by Martyn
Welch introduced a query for the part number of the chip. Unfortunately the
driver aborts loading when this query fails, so currently the driver can not
be used with chips not supporting this query.
I have a data cable for Siemens mobile phones (ID 10ab:10c5) where this is the
case.
With this patch the driver can be loaded even if the part number can not be
queried.

Fixes: cf5276ce7867 ("USB: serial: cp210x: Adding GPIO support for CP2105")
Signed-off-by: Sebastian Frei <dr.nop@xxxxxxx>

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index 2d945c9f975c..a3e301b1eb73 100644
--- a/drivers/usb/serial/cp210x.c
+++ b/drivers/usb/serial/cp210x.c
@@ -352,6 +352,7 @@ static struct usb_serial_driver * const serial_drivers[] = 
{
 #define CP210X_PARTNUM_CP2104	0x04
 #define CP210X_PARTNUM_CP2105	0x05
 #define CP210X_PARTNUM_CP2108	0x08
+#define CP210X_PARTNUM_UNKNOWN	0xFF
 
 /* CP210X_GET_COMM_STATUS returns these 0x13 bytes */
 struct cp210x_comm_status {
@@ -1488,13 +1489,17 @@ static int cp210x_attach(struct usb_serial *serial)
 	if (!priv)
 		return -ENOMEM;
 
+	usb_set_serial_data(serial, priv);
+
 	result = cp210x_read_vendor_block(serial, REQTYPE_DEVICE_TO_HOST,
 					  CP210X_GET_PARTNUM, &priv->partnum,
 					  sizeof(priv->partnum));
-	if (result < 0)
-		goto err_free_priv;
 
-	usb_set_serial_data(serial, priv);
+	if (result < 0) {
+		dev_err(&serial->interface->dev,
+			"querying part number failed, continuing anyways\n");
+		priv->partnum = CP210X_PARTNUM_UNKNOWN;
+	}
 
 	if (priv->partnum == CP210X_PARTNUM_CP2105) {
 		result = cp2105_shared_gpio_init(serial);
@@ -1505,10 +1510,6 @@ static int cp210x_attach(struct usb_serial *serial)
 	}
 
 	return 0;
-err_free_priv:
-	kfree(priv);
-
-	return result;
 }
 
 static void cp210x_disconnect(struct usb_serial *serial)

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