1 // SPDX-License-Identifier: GPL-2.0
2 /*
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>
6 *
7 * This "proprietary tag" header looks like so:
8 *
9 * -------------------------------------------------
10 * | MAC DA | MAC SA | 0x8899 | 2 bytes tag | Type |
11 * -------------------------------------------------
12 *
13 * The 2 bytes tag form a 16 bit big endian word. The exact
14 * meaning has been guessed from packet dumps from ingress
15 * frames, as no working egress traffic has been available
16 * we do not know the format of the egress tags or if they
17 * are even supported.
18 */
19
20 #include <linux/etherdevice.h>
21 #include <linux/bits.h>
22
23 #include "dsa_priv.h"
24
25 #define RTL4_A_HDR_LEN 4
26 #define RTL4_A_ETHERTYPE 0x8899
27 #define RTL4_A_PROTOCOL_SHIFT 12
28 /*
29 * 0x1 = Realtek Remote Control protocol (RRCP)
30 * 0x2/0x3 seems to be used for loopback testing
31 * 0x9 = RTL8306 DSA protocol
32 * 0xa = RTL8366RB DSA protocol
33 */
34 #define RTL4_A_PROTOCOL_RTL8366RB 0xa
35
rtl4a_tag_xmit(struct sk_buff * skb,struct net_device * dev)36 static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
37 struct net_device *dev)
38 {
39 /*
40 * Just let it pass thru, we don't know if it is possible
41 * to tag a frame with the 0x8899 ethertype and direct it
42 * to a specific port, all attempts at reverse-engineering have
43 * ended up with the frames getting dropped.
44 *
45 * The VLAN set-up needs to restrict the frames to the right port.
46 *
47 * If you have documentation on the tagging format for RTL8366RB
48 * (tag type A) then please contribute.
49 */
50 return skb;
51 }
52
rtl4a_tag_rcv(struct sk_buff * skb,struct net_device * dev,struct packet_type * pt)53 static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
54 struct net_device *dev,
55 struct packet_type *pt)
56 {
57 u16 protport;
58 __be16 *p;
59 u16 etype;
60 u8 *tag;
61 u8 prot;
62 u8 port;
63
64 if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
65 return NULL;
66
67 /* The RTL4 header has its own custom Ethertype 0x8899 and that
68 * starts right at the beginning of the packet, after the src
69 * ethernet addr. Apparantly skb->data always points 2 bytes in,
70 * behind the Ethertype.
71 */
72 tag = skb->data - 2;
73 p = (__be16 *)tag;
74 etype = ntohs(*p);
75 if (etype != RTL4_A_ETHERTYPE) {
76 /* Not custom, just pass through */
77 netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
78 return skb;
79 }
80 p = (__be16 *)(tag + 2);
81 protport = ntohs(*p);
82 /* The 4 upper bits are the protocol */
83 prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
84 if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
85 netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
86 return NULL;
87 }
88 port = protport & 0xff;
89
90 skb->dev = dsa_master_find_slave(dev, 0, port);
91 if (!skb->dev) {
92 netdev_dbg(dev, "could not find slave for port %d\n", port);
93 return NULL;
94 }
95
96 /* Remove RTL4 tag and recalculate checksum */
97 skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
98
99 /* Move ethernet DA and SA in front of the data */
100 memmove(skb->data - ETH_HLEN,
101 skb->data - ETH_HLEN - RTL4_A_HDR_LEN,
102 2 * ETH_ALEN);
103
104 skb->offload_fwd_mark = 1;
105
106 return skb;
107 }
108
109 static const struct dsa_device_ops rtl4a_netdev_ops = {
110 .name = "rtl4a",
111 .proto = DSA_TAG_PROTO_RTL4_A,
112 .xmit = rtl4a_tag_xmit,
113 .rcv = rtl4a_tag_rcv,
114 .overhead = RTL4_A_HDR_LEN,
115 };
116 module_dsa_tag_driver(rtl4a_netdev_ops);
117
118 MODULE_LICENSE("GPL");
119 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A);
120