xref: /openbmc/linux/net/dsa/tag_mtk.c (revision 9e3bd0f6)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Mediatek DSA Tag support
4  * Copyright (C) 2017 Landen Chao <landen.chao@mediatek.com>
5  *		      Sean Wang <sean.wang@mediatek.com>
6  */
7 
8 #include <linux/etherdevice.h>
9 #include <linux/if_vlan.h>
10 
11 #include "dsa_priv.h"
12 
13 #define MTK_HDR_LEN		4
14 #define MTK_HDR_XMIT_UNTAGGED		0
15 #define MTK_HDR_XMIT_TAGGED_TPID_8100	1
16 #define MTK_HDR_RECV_SOURCE_PORT_MASK	GENMASK(2, 0)
17 #define MTK_HDR_XMIT_DP_BIT_MASK	GENMASK(5, 0)
18 
19 static struct sk_buff *mtk_tag_xmit(struct sk_buff *skb,
20 				    struct net_device *dev)
21 {
22 	struct dsa_port *dp = dsa_slave_to_port(dev);
23 	u8 *mtk_tag;
24 	bool is_vlan_skb = true;
25 
26 	/* Build the special tag after the MAC Source Address. If VLAN header
27 	 * is present, it's required that VLAN header and special tag is
28 	 * being combined. Only in this way we can allow the switch can parse
29 	 * the both special and VLAN tag at the same time and then look up VLAN
30 	 * table with VID.
31 	 */
32 	if (!skb_vlan_tagged(skb)) {
33 		if (skb_cow_head(skb, MTK_HDR_LEN) < 0)
34 			return NULL;
35 
36 		skb_push(skb, MTK_HDR_LEN);
37 		memmove(skb->data, skb->data + MTK_HDR_LEN, 2 * ETH_ALEN);
38 		is_vlan_skb = false;
39 	}
40 
41 	mtk_tag = skb->data + 2 * ETH_ALEN;
42 
43 	/* Mark tag attribute on special tag insertion to notify hardware
44 	 * whether that's a combined special tag with 802.1Q header.
45 	 */
46 	mtk_tag[0] = is_vlan_skb ? MTK_HDR_XMIT_TAGGED_TPID_8100 :
47 		     MTK_HDR_XMIT_UNTAGGED;
48 	mtk_tag[1] = (1 << dp->index) & MTK_HDR_XMIT_DP_BIT_MASK;
49 
50 	/* Tag control information is kept for 802.1Q */
51 	if (!is_vlan_skb) {
52 		mtk_tag[2] = 0;
53 		mtk_tag[3] = 0;
54 	}
55 
56 	return skb;
57 }
58 
59 static struct sk_buff *mtk_tag_rcv(struct sk_buff *skb, struct net_device *dev,
60 				   struct packet_type *pt)
61 {
62 	int port;
63 	__be16 *phdr, hdr;
64 
65 	if (unlikely(!pskb_may_pull(skb, MTK_HDR_LEN)))
66 		return NULL;
67 
68 	/* The MTK header is added by the switch between src addr
69 	 * and ethertype at this point, skb->data points to 2 bytes
70 	 * after src addr so header should be 2 bytes right before.
71 	 */
72 	phdr = (__be16 *)(skb->data - 2);
73 	hdr = ntohs(*phdr);
74 
75 	/* Remove MTK tag and recalculate checksum. */
76 	skb_pull_rcsum(skb, MTK_HDR_LEN);
77 
78 	memmove(skb->data - ETH_HLEN,
79 		skb->data - ETH_HLEN - MTK_HDR_LEN,
80 		2 * ETH_ALEN);
81 
82 	/* Get source port information */
83 	port = (hdr & MTK_HDR_RECV_SOURCE_PORT_MASK);
84 
85 	skb->dev = dsa_master_find_slave(dev, 0, port);
86 	if (!skb->dev)
87 		return NULL;
88 
89 	return skb;
90 }
91 
92 static int mtk_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
93 				int *offset)
94 {
95 	*offset = 4;
96 	*proto = ((__be16 *)skb->data)[1];
97 
98 	return 0;
99 }
100 
101 static const struct dsa_device_ops mtk_netdev_ops = {
102 	.name		= "mtk",
103 	.proto		= DSA_TAG_PROTO_MTK,
104 	.xmit		= mtk_tag_xmit,
105 	.rcv		= mtk_tag_rcv,
106 	.flow_dissect	= mtk_tag_flow_dissect,
107 	.overhead	= MTK_HDR_LEN,
108 };
109 
110 MODULE_LICENSE("GPL");
111 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_MTK);
112 
113 module_dsa_tag_driver(mtk_netdev_ops);
114