1 // SPDX-License-Identifier: GPL-2.0
3 * Handler for Realtek 4 byte DSA switch tags
4 * Currently only supports protocol "A" found in RTL8366RB
5 * Copyright (c) 2020 Linus Walleij <linus.walleij@linaro.org>
7 * This "proprietary tag" header looks like so:
9 * -------------------------------------------------
10 * | MAC DA | MAC SA | 0x8899 | 2 bytes tag | Type |
11 * -------------------------------------------------
13 * The 2 bytes tag form a 16 bit big endian word. The exact
14 * meaning has been guessed from packet dumps from ingress
18 #include <linux/etherdevice.h>
19 #include <linux/bits.h>
23 #define RTL4_A_HDR_LEN 4
24 #define RTL4_A_ETHERTYPE 0x8899
25 #define RTL4_A_PROTOCOL_SHIFT 12
27 * 0x1 = Realtek Remote Control protocol (RRCP)
28 * 0x2/0x3 seems to be used for loopback testing
29 * 0x9 = RTL8306 DSA protocol
30 * 0xa = RTL8366RB DSA protocol
32 #define RTL4_A_PROTOCOL_RTL8366RB 0xa
34 static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
35 struct net_device *dev)
37 struct dsa_port *dp = dsa_slave_to_port(dev);
42 /* Pad out to at least 60 bytes */
43 if (unlikely(__skb_put_padto(skb, ETH_ZLEN, false)))
46 netdev_dbg(dev, "add realtek tag to package to port %d\n",
48 skb_push(skb, RTL4_A_HDR_LEN);
50 memmove(skb->data, skb->data + RTL4_A_HDR_LEN, 2 * ETH_ALEN);
51 tag = skb->data + 2 * ETH_ALEN;
55 *p = htons(RTL4_A_ETHERTYPE);
57 out = (RTL4_A_PROTOCOL_RTL8366RB << 12) | (2 << 8);
58 /* The lower bits is the port number */
60 p = (__be16 *)(tag + 2);
66 static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
67 struct net_device *dev,
68 struct packet_type *pt)
77 if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
80 /* The RTL4 header has its own custom Ethertype 0x8899 and that
81 * starts right at the beginning of the packet, after the src
82 * ethernet addr. Apparently skb->data always points 2 bytes in,
83 * behind the Ethertype.
88 if (etype != RTL4_A_ETHERTYPE) {
89 /* Not custom, just pass through */
90 netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
93 p = (__be16 *)(tag + 2);
95 /* The 4 upper bits are the protocol */
96 prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
97 if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
98 netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
101 port = protport & 0xff;
103 skb->dev = dsa_master_find_slave(dev, 0, port);
105 netdev_dbg(dev, "could not find slave for port %d\n", port);
109 /* Remove RTL4 tag and recalculate checksum */
110 skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
112 /* Move ethernet DA and SA in front of the data */
113 memmove(skb->data - ETH_HLEN,
114 skb->data - ETH_HLEN - RTL4_A_HDR_LEN,
117 skb->offload_fwd_mark = 1;
122 static const struct dsa_device_ops rtl4a_netdev_ops = {
124 .proto = DSA_TAG_PROTO_RTL4_A,
125 .xmit = rtl4a_tag_xmit,
126 .rcv = rtl4a_tag_rcv,
127 .overhead = RTL4_A_HDR_LEN,
129 module_dsa_tag_driver(rtl4a_netdev_ops);
131 MODULE_LICENSE("GPL");
132 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A);