tag_rtl4_a.c

  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_PROTOCOL_SHIFT	12
 27/*
 28 * 0x1 = Realtek Remote Control protocol (RRCP)
 29 * 0x2/0x3 seems to be used for loopback testing
 30 * 0x9 = RTL8306 DSA protocol
 31 * 0xa = RTL8366RB DSA protocol
 32 */
 33#define RTL4_A_PROTOCOL_RTL8366RB	0xa
 34
 35static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
 36				      struct net_device *dev)
 37{
 38	struct dsa_port *dp = dsa_user_to_port(dev);
 39	__be16 *p;
 40	u8 *tag;
 41	u16 out;
 42
 43	/* Pad out to at least 60 bytes */
 44	if (unlikely(__skb_put_padto(skb, ETH_ZLEN, false)))
 45		return NULL;
 46
 47	netdev_dbg(dev, "add realtek tag to package to port %d\n",
 48		   dp->index);
 49	skb_push(skb, RTL4_A_HDR_LEN);
 50
 51	dsa_alloc_etype_header(skb, RTL4_A_HDR_LEN);
 52	tag = dsa_etype_header_pos_tx(skb);
 53
 54	/* Set Ethertype */
 55	p = (__be16 *)tag;
 56	*p = htons(ETH_P_REALTEK);
 57
 58	out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT);
 59	/* The lower bits indicate the port number */
 60	out |= dsa_xmit_port_mask(skb, dev);
 61
 62	p = (__be16 *)(tag + 2);
 63	*p = htons(out);
 64
 65	return skb;
 66}
 67
 68static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
 69				     struct net_device *dev)
 70{
 71	u16 protport;
 72	__be16 *p;
 73	u16 etype;
 74	u8 *tag;
 75	u8 prot;
 76	u8 port;
 77
 78	if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
 79		return NULL;
 80
 81	tag = dsa_etype_header_pos_rx(skb);
 82	p = (__be16 *)tag;
 83	etype = ntohs(*p);
 84	if (etype != ETH_P_REALTEK) {
 85		/* Not custom, just pass through */
 86		netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
 87		return skb;
 88	}
 89	p = (__be16 *)(tag + 2);
 90	protport = ntohs(*p);
 91	/* The 4 upper bits are the protocol */
 92	prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
 93	if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
 94		netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
 95		return NULL;
 96	}
 97	port = protport & 0xff;
 98
 99	skb->dev = dsa_conduit_find_user(dev, 0, port);
100	if (!skb->dev) {
101		netdev_dbg(dev, "could not find user for port %d\n", port);
102		return NULL;
103	}
104
105	/* Remove RTL4 tag and recalculate checksum */
106	skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
107
108	dsa_strip_etype_header(skb, RTL4_A_HDR_LEN);
109
110	dsa_default_offload_fwd_mark(skb);
111
112	return skb;
113}
114
115static const struct dsa_device_ops rtl4a_netdev_ops = {
116	.name	= RTL4_A_NAME,
117	.proto	= DSA_TAG_PROTO_RTL4_A,
118	.xmit	= rtl4a_tag_xmit,
119	.rcv	= rtl4a_tag_rcv,
120	.needed_headroom = RTL4_A_HDR_LEN,
121};
122module_dsa_tag_driver(rtl4a_netdev_ops);
123
124MODULE_DESCRIPTION("DSA tag driver for Realtek 4 byte protocol A tags");
125MODULE_LICENSE("GPL");
126MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A, RTL4_A_NAME);