can: gs_usb: gs_usb_set_phys_id(): return with error if identify is not supported

Until commit 409c188c ("can: tree-wide: advertise software
timestamping capabilities") the ethtool_ops was only assigned for
devices which support the GS_CAN_FEATURE_IDENTIFY feature. That commit
assigns ethtool_ops unconditionally.

This results on controllers without GS_CAN_FEATURE_IDENTIFY support
for the following ethtool error:

| $ ethtool -p can0 1
| Cannot identify NIC: Broken pipe

Restore the correct error value by checking for
GS_CAN_FEATURE_IDENTIFY in the gs_usb_set_phys_id() function.

| $ ethtool -p can0 1
| Cannot identify NIC: Operation not supported

While there use the variable "netdev" for the "struct net_device"
pointer and "dev" for the "struct gs_can" pointer as in the rest of
the driver.

Fixes: 409c188c ("can: tree-wide: advertise software timestamping capabilities")
Link: http://lore.kernel.org/all/20220818143853.2671854-1-mkl@pengutronix.de
Cc: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/gs_usb.c

@@ -925,17 +925,21 @@ static int gs_usb_set_identify(struct net_device *netdev, bool do_identify)
 }
 
 /* blink LED's for finding the this interface */
-static int gs_usb_set_phys_id(struct net_device *dev,
+static int gs_usb_set_phys_id(struct net_device *netdev,
 			      enum ethtool_phys_id_state state)
 {
+	const struct gs_can *dev = netdev_priv(netdev);
 	int rc = 0;
 
+	if (!(dev->feature & GS_CAN_FEATURE_IDENTIFY))
+		return -EOPNOTSUPP;
+
 	switch (state) {
 	case ETHTOOL_ID_ACTIVE:
-		rc = gs_usb_set_identify(dev, GS_CAN_IDENTIFY_ON);
+		rc = gs_usb_set_identify(netdev, GS_CAN_IDENTIFY_ON);
 		break;
 	case ETHTOOL_ID_INACTIVE:
-		rc = gs_usb_set_identify(dev, GS_CAN_IDENTIFY_OFF);
+		rc = gs_usb_set_identify(netdev, GS_CAN_IDENTIFY_OFF);
 		break;
 	default:
 		break;
@@ -1072,9 +1076,10 @@ static struct gs_can *gs_make_candev(unsigned int channel,
 		dev->feature |= GS_CAN_FEATURE_REQ_USB_QUIRK_LPC546XX |
 			GS_CAN_FEATURE_QUIRK_BREQ_CANTACT_PRO;
 
-	if (le32_to_cpu(dconf->sw_version) > 1)
-		if (feature & GS_CAN_FEATURE_IDENTIFY)
-			netdev->ethtool_ops = &gs_usb_ethtool_ops;
+	/* GS_CAN_FEATURE_IDENTIFY is only supported for sw_version > 1 */
+	if (!(le32_to_cpu(dconf->sw_version) > 1 &&
+	      feature & GS_CAN_FEATURE_IDENTIFY))
+		dev->feature &= ~GS_CAN_FEATURE_IDENTIFY;
 
 	kfree(bt_const);