net-next: dsa: add Mediatek tag RX/TX handler

Add the support for the 4-bytes tag for DSA port distinguishing inserted
allowing receiving and transmitting the packet via the particular port.
The tag is being added after the source MAC address in the ethernet
header.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Signed-off-by: Landen Chao <Landen.Chao@mediatek.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/dsa.h

@@ -32,6 +32,7 @@ enum dsa_tag_protocol {
 	DSA_TAG_PROTO_EDSA,
 	DSA_TAG_PROTO_BRCM,
 	DSA_TAG_PROTO_QCA,
+	DSA_TAG_PROTO_MTK,
 	DSA_TAG_LAST,		/* MUST BE LAST */
 };
 

net/dsa/Kconfig

@@ -31,4 +31,6 @@ config NET_DSA_TAG_TRAILER
 config NET_DSA_TAG_QCA
 	bool
 
+config NET_DSA_TAG_MTK
+	bool
 endif

net/dsa/Makefile

@@ -8,3 +8,4 @@ dsa_core-$(CONFIG_NET_DSA_TAG_DSA) += tag_dsa.o
 dsa_core-$(CONFIG_NET_DSA_TAG_EDSA) += tag_edsa.o
 dsa_core-$(CONFIG_NET_DSA_TAG_TRAILER) += tag_trailer.o
 dsa_core-$(CONFIG_NET_DSA_TAG_QCA) += tag_qca.o
+dsa_core-$(CONFIG_NET_DSA_TAG_MTK) += tag_mtk.o

net/dsa/dsa.c

@@ -53,6 +53,9 @@ const struct dsa_device_ops *dsa_device_ops[DSA_TAG_LAST] = {
 #endif
 #ifdef CONFIG_NET_DSA_TAG_QCA
 	[DSA_TAG_PROTO_QCA] = &qca_netdev_ops,
+#endif
+#ifdef CONFIG_NET_DSA_TAG_MTK
+	[DSA_TAG_PROTO_MTK] = &mtk_netdev_ops,
 #endif
 	[DSA_TAG_PROTO_NONE] = &none_ops,
 };

net/dsa/dsa_priv.h

@@ -85,4 +85,7 @@ extern const struct dsa_device_ops brcm_netdev_ops;
 /* tag_qca.c */
 extern const struct dsa_device_ops qca_netdev_ops;
 
+/* tag_mtk.c */
+extern const struct dsa_device_ops mtk_netdev_ops;
+
 #endif

net/dsa/tag_mtk.c

@@ -0,0 +1,118 @@
+/*
+ * Mediatek DSA Tag support
+ * Copyright (C) 2017 Landen Chao <landen.chao@mediatek.com>
+ *		      Sean Wang <sean.wang@mediatek.com>
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/etherdevice.h>
+#include <net/dsa.h>
+#include "dsa_priv.h"
+
+#define MTK_HDR_LEN		4
+#define MTK_HDR_RECV_SOURCE_PORT_MASK	GENMASK(2, 0)
+#define MTK_HDR_XMIT_DP_BIT_MASK	GENMASK(5, 0)
+
+static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
+				    struct net_device *dev)
+{
+	struct dsa_slave_priv *p = netdev_priv(dev);
+	u8 *mtk_tag;
+
+	if (skb_cow_head(skb, MTK_HDR_LEN) < 0)
+		goto out_free;
+
+	skb_push(skb, MTK_HDR_LEN);
+
+	memmove(skb->data, skb->data + MTK_HDR_LEN, 2 * ETH_ALEN);
+
+	/* Build the tag after the MAC Source Address */
+	mtk_tag = skb->data + 2 * ETH_ALEN;
+	mtk_tag[0] = 0;
+	mtk_tag[1] = (1 << p->dp->index) & MTK_HDR_XMIT_DP_BIT_MASK;
+	mtk_tag[2] = 0;
+	mtk_tag[3] = 0;
+
+	return skb;
+
+out_free:
+	kfree_skb(skb);
+	return NULL;
+}
+
+static int mtk_tag_rcv(struct sk_buff *skb, struct net_device *dev,
+		       struct packet_type *pt, struct net_device *orig_dev)
+{
+	struct dsa_switch_tree *dst = dev->dsa_ptr;
+	struct dsa_switch *ds;
+	int port;
+	__be16 *phdr, hdr;
+
+	if (unlikely(!dst))
+		goto out_drop;
+
+	skb = skb_unshare(skb, GFP_ATOMIC);
+	if (!skb)
+		goto out;
+
+	if (unlikely(!pskb_may_pull(skb, MTK_HDR_LEN)))
+		goto out_drop;
+
+	/* The MTK header is added by the switch between src addr
+	 * and ethertype at this point, skb->data points to 2 bytes
+	 * after src addr so header should be 2 bytes right before.
+	 */
+	phdr = (__be16 *)(skb->data - 2);
+	hdr = ntohs(*phdr);
+
+	/* Remove MTK tag and recalculate checksum. */
+	skb_pull_rcsum(skb, MTK_HDR_LEN);
+
+	memmove(skb->data - ETH_HLEN,
+		skb->data - ETH_HLEN - MTK_HDR_LEN,
+		2 * ETH_ALEN);
+
+	/* This protocol doesn't support cascading multiple
+	 * switches so it's safe to assume the switch is first
+	 * in the tree.
+	 */
+	ds = dst->ds[0];
+	if (!ds)
+		goto out_drop;
+
+	/* Get source port information */
+	port = (hdr & MTK_HDR_RECV_SOURCE_PORT_MASK);
+	if (!ds->ports[port].netdev)
+		goto out_drop;
+
+	/* Update skb & forward the frame accordingly */
+	skb_push(skb, ETH_HLEN);
+
+	skb->pkt_type = PACKET_HOST;
+	skb->dev = ds->ports[port].netdev;
+	skb->protocol = eth_type_trans(skb, skb->dev);
+
+	skb->dev->stats.rx_packets++;
+	skb->dev->stats.rx_bytes += skb->len;
+
+	netif_receive_skb(skb);
+
+	return 0;
+
+out_drop:
+	kfree_skb(skb);
+out:
+	return 0;
+}
+
+const struct dsa_device_ops mtk_netdev_ops = {
+	.xmit	= mtk_tag_xmit,
+	.rcv	= mtk_tag_rcv,
+};