xref: /openbmc/linux/net/dsa/tag_rtl4_a.c (revision 76afff43)
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 
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 
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