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 "dsa_priv.h"
22
23 #define RTL4_A_HDR_LEN 4
24 #define RTL4_A_ETHERTYPE 0x8899
25 #define RTL4_A_PROTOCOL_SHIFT 12
26 /*
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
31 */
32 #define RTL4_A_PROTOCOL_RTL8366RB 0xa
33
rtl4a_tag_xmit(struct sk_buff * skb,struct net_device * dev)34 static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
35 struct net_device *dev)
36 {
37 struct dsa_port *dp = dsa_slave_to_port(dev);
38 __be16 *p;
39 u8 *tag;
40 u16 out;
41
42 /* Pad out to at least 60 bytes */
43 if (unlikely(__skb_put_padto(skb, ETH_ZLEN, false)))
44 return NULL;
45
46 netdev_dbg(dev, "add realtek tag to package to port %d\n",
47 dp->index);
48 skb_push(skb, RTL4_A_HDR_LEN);
49
50 dsa_alloc_etype_header(skb, RTL4_A_HDR_LEN);
51 tag = dsa_etype_header_pos_tx(skb);
52
53 /* Set Ethertype */
54 p = (__be16 *)tag;
55 *p = htons(RTL4_A_ETHERTYPE);
56
57 out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT) | (2 << 8);
58 /* The lower bits indicate the port number */
59 out |= BIT(dp->index);
60
61 p = (__be16 *)(tag + 2);
62 *p = htons(out);
63
64 return skb;
65 }
66
rtl4a_tag_rcv(struct sk_buff * skb,struct net_device * dev)67 static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
68 struct net_device *dev)
69 {
70 u16 protport;
71 __be16 *p;
72 u16 etype;
73 u8 *tag;
74 u8 prot;
75 u8 port;
76
77 if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
78 return NULL;
79
80 tag = dsa_etype_header_pos_rx(skb);
81 p = (__be16 *)tag;
82 etype = ntohs(*p);
83 if (etype != RTL4_A_ETHERTYPE) {
84 /* Not custom, just pass through */
85 netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
86 return skb;
87 }
88 p = (__be16 *)(tag + 2);
89 protport = ntohs(*p);
90 /* The 4 upper bits are the protocol */
91 prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
92 if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
93 netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
94 return NULL;
95 }
96 port = protport & 0xff;
97
98 skb->dev = dsa_master_find_slave(dev, 0, port);
99 if (!skb->dev) {
100 netdev_dbg(dev, "could not find slave for port %d\n", port);
101 return NULL;
102 }
103
104 /* Remove RTL4 tag and recalculate checksum */
105 skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
106
107 dsa_strip_etype_header(skb, RTL4_A_HDR_LEN);
108
109 dsa_default_offload_fwd_mark(skb);
110
111 return skb;
112 }
113
114 static const struct dsa_device_ops rtl4a_netdev_ops = {
115 .name = "rtl4a",
116 .proto = DSA_TAG_PROTO_RTL4_A,
117 .xmit = rtl4a_tag_xmit,
118 .rcv = rtl4a_tag_rcv,
119 .needed_headroom = RTL4_A_HDR_LEN,
120 };
121 module_dsa_tag_driver(rtl4a_netdev_ops);
122
123 MODULE_LICENSE("GPL");
124 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A);
125
