FAILED: patch "[PATCH] USB: serial: cp210x: fix partnum regression" failed to apply to 4.9-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 7eac35ea29dc54cbc8399de84c9bf16553575b89 Mon Sep 17 00:00:00 2001
From: Sebastian Frei <dr.nop@gmx.net>
Date: Tue, 12 Sep 2017 09:50:59 +0200
Subject: [PATCH] USB: serial: cp210x: fix partnum regression

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 probing 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 bound 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@gmx.net>
[ johan: amend commit message; shorten error message and demote to
         warning; drop unnecessary move of usb_set_serial_data() ]
Cc: stable <stable@vger.kernel.org>	# 4.9
Signed-off-by: Johan Hovold <johan@kernel.org>

diff --git a/drivers/usb/serial/cp210x.c b/drivers/usb/serial/cp210x.c
index 2d945c9f975c..8364b44f4c45 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 {
@@ -1491,8 +1492,11 @@ static int cp210x_attach(struct usb_serial *serial)
 	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;
+	if (result < 0) {
+		dev_warn(&serial->interface->dev,
+			 "querying part number failed\n");
+		priv->partnum = CP210X_PARTNUM_UNKNOWN;
+	}
 
 	usb_set_serial_data(serial, priv);
 
@@ -1505,10 +1509,6 @@ 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)