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 |= BIT(dp->index); 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); 127