net/dsa/tag_rtl4_a.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * Handler for Realtek 4 byte DSA switch tags
0004  * Currently only supports protocol "A" found in RTL8366RB
0005  * Copyright (c) 2020 Linus Walleij <linus.walleij@linaro.org>
0006  *
0007  * This "proprietary tag" header looks like so:
0008  *
0009  * -------------------------------------------------
0010  * | MAC DA | MAC SA | 0x8899 | 2 bytes tag | Type |
0011  * -------------------------------------------------
0012  *
0013  * The 2 bytes tag form a 16 bit big endian word. The exact
0014  * meaning has been guessed from packet dumps from ingress
0015  * frames.
0016  */
0017
0018 #include <linux/etherdevice.h>
0019 #include <linux/bits.h>
0020
0021 #include "dsa_priv.h"
0022
0023 #define RTL4_A_HDR_LEN      4
0024 #define RTL4_A_ETHERTYPE    0x8899
0025 #define RTL4_A_PROTOCOL_SHIFT   12
0026 /*
0027  * 0x1 = Realtek Remote Control protocol (RRCP)
0028  * 0x2/0x3 seems to be used for loopback testing
0029  * 0x9 = RTL8306 DSA protocol
0030  * 0xa = RTL8366RB DSA protocol
0031  */
0032 #define RTL4_A_PROTOCOL_RTL8366RB   0xa
0033
0034 static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
0035                       struct net_device *dev)
0036 {
0037     struct dsa_port *dp = dsa_slave_to_port(dev);
0038     __be16 *p;
0039     u8 *tag;
0040     u16 out;
0041
0042     /* Pad out to at least 60 bytes */
0043     if (unlikely(__skb_put_padto(skb, ETH_ZLEN, false)))
0044         return NULL;
0045
0046     netdev_dbg(dev, "add realtek tag to package to port %d\n",
0047            dp->index);
0048     skb_push(skb, RTL4_A_HDR_LEN);
0049
0050     dsa_alloc_etype_header(skb, RTL4_A_HDR_LEN);
0051     tag = dsa_etype_header_pos_tx(skb);
0052
0053     /* Set Ethertype */
0054     p = (__be16 *)tag;
0055     *p = htons(RTL4_A_ETHERTYPE);
0056
0057     out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT);
0058     /* The lower bits indicate the port number */
0059     out |= BIT(dp->index);
0060
0061     p = (__be16 *)(tag + 2);
0062     *p = htons(out);
0063
0064     return skb;
0065 }
0066
0067 static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
0068                      struct net_device *dev)
0069 {
0070     u16 protport;
0071     __be16 *p;
0072     u16 etype;
0073     u8 *tag;
0074     u8 prot;
0075     u8 port;
0076
0077     if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
0078         return NULL;
0079
0080     tag = dsa_etype_header_pos_rx(skb);
0081     p = (__be16 *)tag;
0082     etype = ntohs(*p);
0083     if (etype != RTL4_A_ETHERTYPE) {
0084         /* Not custom, just pass through */
0085         netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
0086         return skb;
0087     }
0088     p = (__be16 *)(tag + 2);
0089     protport = ntohs(*p);
0090     /* The 4 upper bits are the protocol */
0091     prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
0092     if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
0093         netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
0094         return NULL;
0095     }
0096     port = protport & 0xff;
0097
0098     skb->dev = dsa_master_find_slave(dev, 0, port);
0099     if (!skb->dev) {
0100         netdev_dbg(dev, "could not find slave for port %d\n", port);
0101         return NULL;
0102     }
0103
0104     /* Remove RTL4 tag and recalculate checksum */
0105     skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
0106
0107     dsa_strip_etype_header(skb, RTL4_A_HDR_LEN);
0108
0109     dsa_default_offload_fwd_mark(skb);
0110
0111     return skb;
0112 }
0113
0114 static const struct dsa_device_ops rtl4a_netdev_ops = {
0115     .name   = "rtl4a",
0116     .proto  = DSA_TAG_PROTO_RTL4_A,
0117     .xmit   = rtl4a_tag_xmit,
0118     .rcv    = rtl4a_tag_rcv,
0119     .needed_headroom = RTL4_A_HDR_LEN,
0120 };
0121 module_dsa_tag_driver(rtl4a_netdev_ops);
0122
0123 MODULE_LICENSE("GPL");
0124 MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A);