fs_enet: add FEC TX buffer alignment workaround for MPC5121

MPC5121 FEC requeries 4-byte alignmnent for TX data buffers.
This patch is a work around that copies misaligned tx packets
to an aligned skb before sending.
Signed-off-by: John Rigby <jcrigby@gmail.com>
Signed-off-by: Piotr Ziecik <kosmo@semihalf.com>
Signed-off-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Anatolij Gustschin <agust@denx.de>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/fs_enet/fs_enet-main.c

@@ -580,6 +580,40 @@ void fs_cleanup_bds(struct net_device *dev)
 
 /**********************************************************************************/
 
+#ifdef CONFIG_FS_ENET_MPC5121_FEC
+/*
+ * MPC5121 FEC requeries 4-byte alignment for TX data buffer!
+ */
+static struct sk_buff *tx_skb_align_workaround(struct net_device *dev,
+					       struct sk_buff *skb)
+{
+	struct sk_buff *new_skb;
+	struct fs_enet_private *fep = netdev_priv(dev);
+
+	/* Alloc new skb */
+	new_skb = dev_alloc_skb(skb->len + 4);
+	if (!new_skb) {
+		if (net_ratelimit()) {
+			dev_warn(fep->dev,
+				 "Memory squeeze, dropping tx packet.\n");
+		}
+		return NULL;
+	}
+
+	/* Make sure new skb is properly aligned */
+	skb_align(new_skb, 4);
+
+	/* Copy data to new skb ... */
+	skb_copy_from_linear_data(skb, new_skb->data, skb->len);
+	skb_put(new_skb, skb->len);
+
+	/* ... and free an old one */
+	dev_kfree_skb_any(skb);
+
+	return new_skb;
+}
+#endif
+
 static int fs_enet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct fs_enet_private *fep = netdev_priv(dev);
@@ -588,6 +622,19 @@ static int fs_enet_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	u16 sc;
 	unsigned long flags;
 
+#ifdef CONFIG_FS_ENET_MPC5121_FEC
+	if (((unsigned long)skb->data) & 0x3) {
+		skb = tx_skb_align_workaround(dev, skb);
+		if (!skb) {
+			/*
+			 * We have lost packet due to memory allocation error
+			 * in tx_skb_align_workaround(). Hopefully original
+			 * skb is still valid, so try transmit it later.
+			 */
+			return NETDEV_TX_BUSY;
+		}
+	}
+#endif
 	spin_lock_irqsave(&fep->tx_lock, flags);
 
 	/*