Re: [RFC PATCH 1/2 net-next] net: dsa: initial MT7628 special tag driver

[Vladimir Oltean <olteanv@gmail.com>]

On Sat, Feb 28, 2026 at 08:52:42PM +0200, Joris Vaisvila wrote:
> +#include <linux/etherdevice.h>
> +#include <linux/dsa/8021q.h>
> +#include <net/dsa.h>
> +
> +#include "tag.h"
> +
> +/* 

You have a trailing whitespace here.

> + * MT7628 uses the ralink special tag. It merges the VLAN TPID with source
> + * port ID on RX and target port bitmap on TX.
> + *
> + * The switch forwarding is controlled with VLANs, so each port is put in a
> + * standalone VLAN using tag_8021q. Double tag is enabled to simulate VLAN
> + * unaware ports.
> + *
> + * A VLAN tag is constructed on egress to target the standalone VLAN and port.
> + * The outer VLAN tag is parsed and removed on ingress.
> + */
> +
> +#define MT7628_TAG_NAME "tag_mt7628"

No other protocol name starts with "tag_". This is exported to user
space (cat /sys/class/net/<conduit>/dsa/tagging), it's good to have some
uniformity.

> +
> +#define SPECIAL_HEADER_RECV_SOURCE_PORT_MASK GENMASK(2, 0)
> +#define SPECIAL_TAG_LEN 4
> +
> +static struct sk_buff *dsa_user_special_xmit(struct sk_buff *skb,
> +					     struct net_device *dev)
> +{
> +	struct dsa_port *dp = dsa_user_to_port(dev);
> +	u16 xmit_vlan = dsa_tag_8021q_standalone_vid(dp);
> +	u8 *special_tag;
> +
> +	skb_push(skb, SPECIAL_TAG_LEN);
> +	dsa_alloc_etype_header(skb, SPECIAL_TAG_LEN);
> +
> +	special_tag = dsa_etype_header_pos_tx(skb);
> +
> +	special_tag[0] = ETH_P_8021Q >> 8;
> +	special_tag[1] = BIT(dp->index);

We don't do BIT(dp->index) anymore. It's wrapped around a
dsa_xmit_port_mask() helper, which also gives you some HSR TX offloading
if you set the offload pointers to dsa_port_simple_hsr_join() and
dsa_port_simple_hsr_leave().

> +
> +	special_tag[2] = xmit_vlan >> 8;
> +	special_tag[3] = xmit_vlan & 0xff;
> +	return skb;
> +}