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// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (c) 2026, Joris Vaisvila <joey@tinyisr.com>
* MT7628 switch tag support
*/
#include <linux/etherdevice.h>
#include <linux/dsa/8021q.h>
#include <net/dsa.h>
#include "tag.h"
/*
* The MT7628 tag is encoded in the VLAN TPID field.
* On TX the lower 6 bits encode the destination port bitmask.
* On RX the lower 3 bits encode the source port number.
*
* The switch hardware will not modify the TPID of an incoming packet if it is
* already VLAN tagged. To work around this the switch is configured to always
* append a tag_8021q standalone VLAN tag for each port. That means we can
* safely strip the outer VLAN tag after parsing it.
*
* A VLAN tag is constructed on egress to target the standalone VLAN and
* destination port.
*/
#define MT7628_TAG_NAME "mt7628"
#define MT7628_TAG_TX_PORT GENMASK(5, 0)
#define MT7628_TAG_RX_PORT GENMASK(2, 0)
#define MT7628_TAG_LEN 4
static struct sk_buff *mt7628_tag_xmit(struct sk_buff *skb,
struct net_device *dev)
{
struct dsa_port *dp;
u16 xmit_vlan;
__be16 *tag;
dp = dsa_user_to_port(dev);
xmit_vlan = dsa_tag_8021q_standalone_vid(dp);
skb_push(skb, MT7628_TAG_LEN);
dsa_alloc_etype_header(skb, MT7628_TAG_LEN);
tag = dsa_etype_header_pos_tx(skb);
tag[0] = htons(ETH_P_8021Q |
FIELD_PREP(MT7628_TAG_TX_PORT,
dsa_xmit_port_mask(skb, dev)));
tag[1] = htons(xmit_vlan);
return skb;
}
static struct sk_buff *mt7628_tag_rcv(struct sk_buff *skb,
struct net_device *dev)
{
__be16 *phdr;
if (unlikely(!pskb_may_pull(skb, MT7628_TAG_LEN))) {
kfree_skb(skb);
return NULL;
}
phdr = dsa_etype_header_pos_rx(skb);
skb->dev =
dsa_conduit_find_user(dev, 0,
FIELD_GET(MT7628_TAG_RX_PORT, ntohs(*phdr)));
if (!skb->dev) {
kfree_skb(skb);
return NULL;
}
skb_pull_rcsum(skb, MT7628_TAG_LEN);
dsa_strip_etype_header(skb, MT7628_TAG_LEN);
dsa_default_offload_fwd_mark(skb);
return skb;
}
static const struct dsa_device_ops mt7628_tag_ops = {
.name = MT7628_TAG_NAME,
.proto = DSA_TAG_PROTO_MT7628,
.xmit = mt7628_tag_xmit,
.rcv = mt7628_tag_rcv,
.needed_headroom = MT7628_TAG_LEN,
};
module_dsa_tag_driver(mt7628_tag_ops);
MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_MT7628, MT7628_TAG_NAME);
MODULE_DESCRIPTION("DSA tag driver for MT7628 switch");
MODULE_LICENSE("GPL");
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