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, as no working egress traffic has been available 16 * we do not know the format of the egress tags or if they 17 * are even supported. 18 */ 19 20 #include <linux/etherdevice.h> 21 #include <linux/bits.h> 22 23 #include "dsa_priv.h" 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 /* 40 * Just let it pass thru, we don't know if it is possible 41 * to tag a frame with the 0x8899 ethertype and direct it 42 * to a specific port, all attempts at reverse-engineering have 43 * ended up with the frames getting dropped. 44 * 45 * The VLAN set-up needs to restrict the frames to the right port. 46 * 47 * If you have documentation on the tagging format for RTL8366RB 48 * (tag type A) then please contribute. 49 */ 50 return skb; 51 } 52 53 static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb, 54 struct net_device *dev, 55 struct packet_type *pt) 56 { 57 u16 protport; 58 __be16 *p; 59 u16 etype; 60 u8 *tag; 61 u8 prot; 62 u8 port; 63 64 if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN))) 65 return NULL; 66 67 /* The RTL4 header has its own custom Ethertype 0x8899 and that 68 * starts right at the beginning of the packet, after the src 69 * ethernet addr. Apparantly skb->data always points 2 bytes in, 70 * behind the Ethertype. 71 */ 72 tag = skb->data - 2; 73 p = (__be16 *)tag; 74 etype = ntohs(*p); 75 if (etype != RTL4_A_ETHERTYPE) { 76 /* Not custom, just pass through */ 77 netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype); 78 return skb; 79 } 80 p = (__be16 *)(tag + 2); 81 protport = ntohs(*p); 82 /* The 4 upper bits are the protocol */ 83 prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f; 84 if (prot != RTL4_A_PROTOCOL_RTL8366RB) { 85 netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot); 86 return NULL; 87 } 88 port = protport & 0xff; 89 90 skb->dev = dsa_master_find_slave(dev, 0, port); 91 if (!skb->dev) { 92 netdev_dbg(dev, "could not find slave for port %d\n", port); 93 return NULL; 94 } 95 96 /* Remove RTL4 tag and recalculate checksum */ 97 skb_pull_rcsum(skb, RTL4_A_HDR_LEN); 98 99 /* Move ethernet DA and SA in front of the data */ 100 memmove(skb->data - ETH_HLEN, 101 skb->data - ETH_HLEN - RTL4_A_HDR_LEN, 102 2 * ETH_ALEN); 103 104 skb->offload_fwd_mark = 1; 105 106 return skb; 107 } 108 109 static int rtl4a_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto, 110 int *offset) 111 { 112 *offset = RTL4_A_HDR_LEN; 113 /* Skip past the tag and fetch the encapsulated Ethertype */ 114 *proto = ((__be16 *)skb->data)[1]; 115 116 return 0; 117 } 118 119 static const struct dsa_device_ops rtl4a_netdev_ops = { 120 .name = "rtl4a", 121 .proto = DSA_TAG_PROTO_RTL4_A, 122 .xmit = rtl4a_tag_xmit, 123 .rcv = rtl4a_tag_rcv, 124 .flow_dissect = rtl4a_tag_flow_dissect, 125 .overhead = RTL4_A_HDR_LEN, 126 }; 127 module_dsa_tag_driver(rtl4a_netdev_ops); 128 129 MODULE_LICENSE("GPL"); 130 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A); 131