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// SPDX-License-Identifier: GPL-2.0
/*
* Handler for Realtek 4 byte DSA switch tags
* Currently only supports protocol "A" found in RTL8366RB
* Copyright (c) 2020 Linus Walleij <linus.walleij@linaro.org>
*
* This "proprietary tag" header looks like so:
*
* -------------------------------------------------
* | MAC DA | MAC SA | 0x8899 | 2 bytes tag | Type |
* -------------------------------------------------
*
* The 2 bytes tag form a 16 bit big endian word. The exact
* meaning has been guessed from packet dumps from ingress
* frames, as no working egress traffic has been available
* we do not know the format of the egress tags or if they
* are even supported.
*/
#include <linux/etherdevice.h>
#include <linux/bits.h>
#include "dsa_priv.h"
#define RTL4_A_HDR_LEN 4
#define RTL4_A_ETHERTYPE 0x8899
#define RTL4_A_PROTOCOL_SHIFT 12
/*
* 0x1 = Realtek Remote Control protocol (RRCP)
* 0x2/0x3 seems to be used for loopback testing
* 0x9 = RTL8306 DSA protocol
* 0xa = RTL8366RB DSA protocol
*/
#define RTL4_A_PROTOCOL_RTL8366RB 0xa
static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
struct net_device *dev)
{
/*
* Just let it pass thru, we don't know if it is possible
* to tag a frame with the 0x8899 ethertype and direct it
* to a specific port, all attempts at reverse-engineering have
* ended up with the frames getting dropped.
*
* The VLAN set-up needs to restrict the frames to the right port.
*
* If you have documentation on the tagging format for RTL8366RB
* (tag type A) then please contribute.
*/
return skb;
}
static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
struct net_device *dev,
struct packet_type *pt)
{
u16 protport;
__be16 *p;
u16 etype;
u8 *tag;
u8 prot;
u8 port;
if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
return NULL;
/* The RTL4 header has its own custom Ethertype 0x8899 and that
* starts right at the beginning of the packet, after the src
* ethernet addr. Apparantly skb->data always points 2 bytes in,
* behind the Ethertype.
*/
tag = skb->data - 2;
p = (__be16 *)tag;
etype = ntohs(*p);
if (etype != RTL4_A_ETHERTYPE) {
/* Not custom, just pass through */
netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
return skb;
}
p = (__be16 *)(tag + 2);
protport = ntohs(*p);
/* The 4 upper bits are the protocol */
prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
return NULL;
}
port = protport & 0xff;
skb->dev = dsa_master_find_slave(dev, 0, port);
if (!skb->dev) {
netdev_dbg(dev, "could not find slave for port %d\n", port);
return NULL;
}
/* Remove RTL4 tag and recalculate checksum */
skb_pull_rcsum(skb, RTL4_A_HDR_LEN);
/* Move ethernet DA and SA in front of the data */
memmove(skb->data - ETH_HLEN,
skb->data - ETH_HLEN - RTL4_A_HDR_LEN,
2 * ETH_ALEN);
skb->offload_fwd_mark = 1;
return skb;
}
static int rtl4a_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
int *offset)
{
*offset = RTL4_A_HDR_LEN;
/* Skip past the tag and fetch the encapsulated Ethertype */
*proto = ((__be16 *)skb->data)[1];
return 0;
}
static const struct dsa_device_ops rtl4a_netdev_ops = {
.name = "rtl4a",
.proto = DSA_TAG_PROTO_RTL4_A,
.xmit = rtl4a_tag_xmit,
.rcv = rtl4a_tag_rcv,
.flow_dissect = rtl4a_tag_flow_dissect,
.overhead = RTL4_A_HDR_LEN,
};
module_dsa_tag_driver(rtl4a_netdev_ops);
MODULE_LICENSE("GPL");
MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A);
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