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.
16 */
17
18 #include <linux/etherdevice.h>
19 #include <linux/bits.h>
20
21 #include "tag.h"
22
23 #define RTL4_A_NAME "rtl4a"
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 struct dsa_port *dp = dsa_slave_to_port(dev);
40 __be16 *p;
41 u8 *tag;
42 u16 out;
43
44 /* Pad out to at least 60 bytes */
45 if (unlikely(__skb_put_padto(skb, ETH_ZLEN, false)))
46 return NULL;
47
48 netdev_dbg(dev, "add realtek tag to package to port %d\n",
49 dp->index);
50 skb_push(skb, RTL4_A_HDR_LEN);
51
52 dsa_alloc_etype_header(skb, RTL4_A_HDR_LEN);
53 tag = dsa_etype_header_pos_tx(skb);
54
55 /* Set Ethertype */
56 p = (__be16 *)tag;
57 *p = htons(RTL4_A_ETHERTYPE);
58
59 out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT);
60 /* The lower bits indicate the port number */
61 out |= BIT(dp->index);
62
63 p = (__be16 *)(tag + 2);
64 *p = htons(out);
65
66 return skb;
67 }
68
rtl4a_tag_rcv(struct sk_buff * skb,struct net_device * dev)69 static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
70 struct net_device *dev)
71 {
72 u16 protport;
73 __be16 *p;
74 u16 etype;
75 u8 *tag;
76 u8 prot;
77 u8 port;
78
79 if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
80 return NULL;
81
82 tag = dsa_etype_header_pos_rx(skb);
83 p = (__be16 *)tag;
84 etype = ntohs(*p);
85 if (etype != RTL4_A_ETHERTYPE) {
86 /* Not custom, just pass through */
87 netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
88 return skb;
89 }
90 p = (__be16 *)(tag + 2);
91 protport = ntohs(*p);
92 /* The 4 upper bits are the protocol */
93 prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
94 if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
95 netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
96 return NULL;
97 }
98 port = protport & 0xff;
99
100 skb->dev = dsa_master_find_slave(dev, 0, port);
101 if (!skb->dev) {
102 netdev_dbg(dev, "could not find slave for port %d\n", port);
103 return NULL;
104 }
105
106 /* Remove RTL4 tag and recalculate checksum */
107 skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
108
109 dsa_strip_etype_header(skb, RTL4_A_HDR_LEN);
110
111 dsa_default_offload_fwd_mark(skb);
112
113 return skb;
114 }
115
116 static const struct dsa_device_ops rtl4a_netdev_ops = {
117 .name = RTL4_A_NAME,
118 .proto = DSA_TAG_PROTO_RTL4_A,
119 .xmit = rtl4a_tag_xmit,
120 .rcv = rtl4a_tag_rcv,
121 .needed_headroom = RTL4_A_HDR_LEN,
122 };
123 module_dsa_tag_driver(rtl4a_netdev_ops);
124
125 MODULE_LICENSE("GPL");
126 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A, RTL4_A_NAME);
127