can: add can_free_echo_skb() for upcoming drivers

This patch adds the function can_free_echo_skb to the CAN
device interface to allow upcoming drivers to release echo
skb's in case of error.
Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/can/dev.c

@@ -315,13 +315,29 @@ void can_get_echo_skb(struct net_device *dev, int idx)
 {
 	struct can_priv *priv = netdev_priv(dev);
 
-	if ((dev->flags & IFF_ECHO) && priv->echo_skb[idx]) {
+	if (priv->echo_skb[idx]) {
 		netif_rx(priv->echo_skb[idx]);
 		priv->echo_skb[idx] = NULL;
 	}
 }
 EXPORT_SYMBOL_GPL(can_get_echo_skb);
 
+/*
+  * Remove the skb from the stack and free it.
+  *
+  * The function is typically called when TX failed.
+  */
+void can_free_echo_skb(struct net_device *dev, int idx)
+{
+	struct can_priv *priv = netdev_priv(dev);
+
+	if (priv->echo_skb[idx]) {
+		kfree_skb(priv->echo_skb[idx]);
+		priv->echo_skb[idx] = NULL;
+	}
+}
+EXPORT_SYMBOL_GPL(can_free_echo_skb);
+
 /*
  * CAN device restart for bus-off recovery
  */

include/linux/can/dev.h

@@ -66,5 +66,6 @@ void can_bus_off(struct net_device *dev);
 
 void can_put_echo_skb(struct sk_buff *skb, struct net_device *dev, int idx);
 void can_get_echo_skb(struct net_device *dev, int idx);
+void can_free_echo_skb(struct net_device *dev, int idx);
 
 #endif /* CAN_DEV_H */