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

  /*
   * net/dsa/tag_dsa.c - (Non-ethertype) DSA tagging

   * Copyright (c) 2008-2009 Marvell Semiconductor

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

  #include <linux/slab.h>

  #include "dsa_priv.h"
  
  #define DSA_HLEN	4

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

  {

  	struct dsa_port *dp = dsa_slave_to_port(dev);

  	u8 *dsa_header;

  	/*
  	 * Convert the outermost 802.1q tag to a DSA tag for tagged
  	 * packets, or insert a DSA tag between the addresses and
  	 * the ethertype field for untagged packets.
  	 */
  	if (skb->protocol == htons(ETH_P_8021Q)) {
  		if (skb_cow_head(skb, 0) < 0)

  			return NULL;

  
  		/*
  		 * Construct tagged FROM_CPU DSA tag from 802.1q tag.
  		 */
  		dsa_header = skb->data + 2 * ETH_ALEN;

  		dsa_header[0] = 0x60 | dp->ds->index;
  		dsa_header[1] = dp->index << 3;

  
  		/*
  		 * Move CFI field from byte 2 to byte 1.
  		 */
  		if (dsa_header[2] & 0x10) {
  			dsa_header[1] |= 0x01;
  			dsa_header[2] &= ~0x10;
  		}
  	} else {
  		if (skb_cow_head(skb, DSA_HLEN) < 0)

  			return NULL;

  		skb_push(skb, DSA_HLEN);
  
  		memmove(skb->data, skb->data + DSA_HLEN, 2 * ETH_ALEN);
  
  		/*
  		 * Construct untagged FROM_CPU DSA tag.
  		 */
  		dsa_header = skb->data + 2 * ETH_ALEN;

  		dsa_header[0] = 0x40 | dp->ds->index;
  		dsa_header[1] = dp->index << 3;

  		dsa_header[2] = 0x00;
  		dsa_header[3] = 0x00;
  	}

  	return skb;

  }

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

  			       struct packet_type *pt)

  {

  	u8 *dsa_header;

  	int source_device;

  	int source_port;

  	if (unlikely(!pskb_may_pull(skb, DSA_HLEN)))

  		return NULL;

  
  	/*
  	 * The ethertype field is part of the DSA header.
  	 */
  	dsa_header = skb->data - 2;
  
  	/*

  	 * Check that frame type is either TO_CPU or FORWARD.

  	 */

  	if ((dsa_header[0] & 0xc0) != 0x00 && (dsa_header[0] & 0xc0) != 0xc0)

  		return NULL;

  
  	/*

  	 * Determine source device and port.

  	 */

  	source_device = dsa_header[0] & 0x1f;

  	source_port = (dsa_header[1] >> 3) & 0x1f;

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

  	if (!skb->dev)

  		return NULL;

  
  	/*
  	 * Convert the DSA header to an 802.1q header if the 'tagged'
  	 * bit in the DSA header is set.  If the 'tagged' bit is clear,
  	 * delete the DSA header entirely.
  	 */
  	if (dsa_header[0] & 0x20) {
  		u8 new_header[4];
  
  		/*
  		 * Insert 802.1q ethertype and copy the VLAN-related
  		 * fields, but clear the bit that will hold CFI (since
  		 * DSA uses that bit location for another purpose).
  		 */
  		new_header[0] = (ETH_P_8021Q >> 8) & 0xff;
  		new_header[1] = ETH_P_8021Q & 0xff;
  		new_header[2] = dsa_header[2] & ~0x10;
  		new_header[3] = dsa_header[3];
  
  		/*
  		 * Move CFI bit from its place in the DSA header to
  		 * its 802.1q-designated place.
  		 */
  		if (dsa_header[1] & 0x01)
  			new_header[2] |= 0x10;
  
  		/*
  		 * Update packet checksum if skb is CHECKSUM_COMPLETE.
  		 */
  		if (skb->ip_summed == CHECKSUM_COMPLETE) {
  			__wsum c = skb->csum;
  			c = csum_add(c, csum_partial(new_header + 2, 2, 0));
  			c = csum_sub(c, csum_partial(dsa_header + 2, 2, 0));
  			skb->csum = c;
  		}
  
  		memcpy(dsa_header, new_header, DSA_HLEN);
  	} else {
  		/*
  		 * Remove DSA tag and update checksum.
  		 */
  		skb_pull_rcsum(skb, DSA_HLEN);
  		memmove(skb->data - ETH_HLEN,
  			skb->data - ETH_HLEN - DSA_HLEN,
  			2 * ETH_ALEN);
  	}

  	skb->offload_fwd_mark = 1;

  	return skb;

  }

  static int dsa_tag_flow_dissect(const struct sk_buff *skb, __be16 *proto,
  				int *offset)
  {
  	*offset = 4;
  	*proto = ((__be16 *)skb->data)[1];
  	return 0;
  }

  static const struct dsa_device_ops dsa_netdev_ops = {

  	.name	= "dsa",

  	.proto	= DSA_TAG_PROTO_DSA,

  	.xmit	= dsa_xmit,
  	.rcv	= dsa_rcv,

  	.flow_dissect   = dsa_tag_flow_dissect,

  	.overhead = DSA_HLEN,

  };

  MODULE_LICENSE("GPL");

  MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_DSA);

  
  module_dsa_tag_driver(dsa_netdev_ops);