// SPDX-License-Identifier: GPL-2.0+

  /*
   * net/dsa/tag_trailer.c - Trailer tag format handling

   * Copyright (c) 2008-2009 Marvell Semiconductor

   */
  
  #include <linux/etherdevice.h>
  #include <linux/list.h>

  #include <linux/slab.h>

  #include "dsa_priv.h"

  static struct sk_buff *trailer_xmit(struct sk_buff *skb, struct net_device *dev)

  {

  	struct dsa_port *dp = dsa_slave_to_port(dev);

  	struct sk_buff *nskb;
  	int padlen;
  	u8 *trailer;

  	/*
  	 * We have to make sure that the trailer ends up as the very
  	 * last 4 bytes of the packet.  This means that we have to pad
  	 * the packet to the minimum ethernet frame size, if necessary,
  	 * before adding the trailer.
  	 */
  	padlen = 0;
  	if (skb->len < 60)
  		padlen = 60 - skb->len;
  
  	nskb = alloc_skb(NET_IP_ALIGN + skb->len + padlen + 4, GFP_ATOMIC);

  	if (!nskb)

  		return NULL;

  	skb_reserve(nskb, NET_IP_ALIGN);
  
  	skb_reset_mac_header(nskb);
  	skb_set_network_header(nskb, skb_network_header(skb) - skb->head);
  	skb_set_transport_header(nskb, skb_transport_header(skb) - skb->head);
  	skb_copy_and_csum_dev(skb, skb_put(nskb, skb->len));

  	consume_skb(skb);

  
  	if (padlen) {

  		skb_put_zero(nskb, padlen);

  	}
  
  	trailer = skb_put(nskb, 4);
  	trailer[0] = 0x80;

  	trailer[1] = 1 << dp->index;

  	trailer[2] = 0x10;
  	trailer[3] = 0x00;

  	return nskb;

  }

  static struct sk_buff *trailer_rcv(struct sk_buff *skb, struct net_device *dev,

  				   struct packet_type *pt)

  {

  	u8 *trailer;
  	int source_port;

  	if (skb_linearize(skb))

  		return NULL;

  
  	trailer = skb_tail_pointer(skb) - 4;
  	if (trailer[0] != 0x80 || (trailer[1] & 0xf8) != 0x00 ||

  	    (trailer[2] & 0xef) != 0x00 || trailer[3] != 0x00)

  		return NULL;

  
  	source_port = trailer[1] & 7;

  	skb->dev = dsa_master_find_slave(dev, 0, source_port);

  	if (!skb->dev)

  		return NULL;

  	if (pskb_trim_rcsum(skb, skb->len - 4))
  		return NULL;

  	return skb;

  }

  static const struct dsa_device_ops trailer_netdev_ops = {

  	.name	= "trailer",

  	.proto	= DSA_TAG_PROTO_TRAILER,

  	.xmit	= trailer_xmit,
  	.rcv	= trailer_rcv,

  	.overhead = 4,

  };

  MODULE_LICENSE("GPL");

  MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_TRAILER);

  
  module_dsa_tag_driver(trailer_netdev_ops);