Subject: Re: [PATCH net-next 4/6] net: dsa: tag_rtl8_4: add realtek 8 byte protocol 4 tag

From: DENG Qingfang <[email-masked]>
Date: Wed, 13 Oct 2021 17:45:16 +0800

On Tue, Oct 12, 2021 at 02:35:53PM +0200, Alvin Šipraga wrote:
> +static struct sk_buff *rtl8_4_tag_rcv(struct sk_buff *skb,
> +				      struct net_device *dev)
> +{
> +	__be16 *tag;
> +	u16 etype;
> +	u8 proto;
> +	u8 port;
> +
> +	if (unlikely(!pskb_may_pull(skb, RTL8_4_TAG_LEN)))
> +		return NULL;
> +
> +	tag = dsa_etype_header_pos_rx(skb);
> +
> +	/* Parse Realtek EtherType */
> +	etype = ntohs(tag[0]);
> +	if (unlikely(etype != ETH_P_REALTEK)) {
> +		dev_warn_ratelimited(&dev->dev,
> +				     "non-realtek ethertype 0x%04x\n", etype);
> +		return NULL;
> +	}
> +
> +	/* Parse Protocol */
> +	proto = ntohs(tag[1]) >> 8;
> +	if (unlikely(proto != RTL8_4_PROTOCOL_RTL8365MB)) {
> +		dev_warn_ratelimited(&dev->dev,
> +				     "unknown realtek protocol 0x%02x\n",
> +				     proto);
> +		return NULL;
> +	}
> +
> +	/* Parse TX (switch->CPU) */
> +	port = ntohs(tag[3]) & 0xf; /* Port number is the LSB 4 bits */
> +	skb->dev = dsa_master_find_slave(dev, 0, port);
> +	if (!skb->dev) {
> +		dev_warn_ratelimited(&dev->dev,
> +				     "could not find slave for port %d\n",
> +				     port);
> +		return NULL;
> +	}
> +
> +	/* Remove tag and recalculate checksum */
> +	skb_pull_rcsum(skb, RTL8_4_TAG_LEN);
> +
> +	dsa_strip_etype_header(skb, RTL8_4_TAG_LEN);
> +
> +	dsa_default_offload_fwd_mark(skb);

This should not be set if the REASON is trapped to CPU.

> +
> +	return skb;
> +}