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 dsa_alloc_etype_header(skb, RTL4_A_HDR_LEN);
51 tag = dsa_etype_header_pos_tx(skb);
55 *p = htons(RTL4_A_ETHERTYPE);
57 out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT);
58 /* The lower bits indicate the port number */
59 out |= BIT(dp->index);
61 p = (__be16 *)(tag + 2);
67 static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
68 struct net_device *dev)
77 if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
80 tag = dsa_etype_header_pos_rx(skb);
83 if (etype != RTL4_A_ETHERTYPE) {
84 /* Not custom, just pass through */
85 netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
88 p = (__be16 *)(tag + 2);
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);
96 port = protport & 0xff;
98 skb->dev = dsa_master_find_slave(dev, 0, port);
100 netdev_dbg(dev, "could not find slave for port %d\n", port);
104 /* Remove RTL4 tag and recalculate checksum */
105 skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
107 dsa_strip_etype_header(skb, RTL4_A_HDR_LEN);
109 dsa_default_offload_fwd_mark(skb);
114 static const struct dsa_device_ops rtl4a_netdev_ops = {
116 .proto = DSA_TAG_PROTO_RTL4_A,
117 .xmit = rtl4a_tag_xmit,
118 .rcv = rtl4a_tag_rcv,
119 .needed_headroom = RTL4_A_HDR_LEN,
121 module_dsa_tag_driver(rtl4a_netdev_ops);
123 MODULE_LICENSE("GPL");
124 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A);