// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2017 Pengutronix, Juergen Borleis <jbe@pengutronix.de>
 */
#include <linux/dsa/lan9303.h>
#include <linux/etherdevice.h>
#include <linux/list.h>
#include <linux/slab.h>

#include "tag.h"

/* To define the outgoing port and to discover the incoming port a regular
 * VLAN tag is used by the LAN9303. But its VID meaning is 'special':
 *
 *       Dest MAC       Src MAC        TAG    Type
 * ...| 1 2 3 4 5 6 | 1 2 3 4 5 6 | 1 2 3 4 | 1 2 |...
 *                                |<------->|
 * TAG:
 *    |<------------->|
 *    |  1  2 | 3  4  |
 *      TPID    VID
 *     0x8100
 *
 * VID bit 3 indicates a request for an ALR lookup.
 *
 * If VID bit 3 is zero, then bits 0 and 1 specify the destination port
 * (0, 1, 2) or broadcast (3) or the source port (1, 2).
 *
 * VID bit 4 is used to specify if the STP port state should be overridden.
 * Required when no forwarding between the external ports should happen.
 */

#define LAN9303_NAME "lan9303"

#define LAN9303_TAG_LEN 4
# define LAN9303_TAG_TX_USE_ALR BIT(3)
# define LAN9303_TAG_TX_STP_OVERRIDE BIT(4)
# define LAN9303_TAG_RX_IGMP BIT(3)
# define LAN9303_TAG_RX_STP BIT(4)
# define LAN9303_TAG_RX_TRAPPED_TO_CPU (LAN9303_TAG_RX_IGMP | \
                                        LAN9303_TAG_RX_STP)

/* Decide whether to transmit using ALR lookup, or transmit directly to
 * port using tag. ALR learning is performed only when using ALR lookup.
 * If the two external ports are bridged and the frame is unicast,
 * then use ALR lookup to allow ALR learning on CPU port.
 * Otherwise transmit directly to port with STP state override.
 * See also: lan9303_separate_ports() and lan9303.pdf 6.4.10.1
 */
static int lan9303_xmit_use_arl(struct dsa_port *dp, u8 *dest_addr)
{
        struct lan9303 *chip = dp->ds->priv;

        return chip->is_bridged && !is_multicast_ether_addr(dest_addr);
}

static struct sk_buff *lan9303_xmit(struct sk_buff *skb, struct net_device *dev)
{
        struct dsa_port *dp = dsa_user_to_port(dev);
        __be16 *lan9303_tag;
        u16 tag;

        /* provide 'LAN9303_TAG_LEN' bytes additional space */
        skb_push(skb, LAN9303_TAG_LEN);

        /* make room between MACs and Ether-Type */
        dsa_alloc_etype_header(skb, LAN9303_TAG_LEN);

        lan9303_tag = dsa_etype_header_pos_tx(skb);

        tag = lan9303_xmit_use_arl(dp, skb->data) ?
                LAN9303_TAG_TX_USE_ALR :
                dp->index | LAN9303_TAG_TX_STP_OVERRIDE;
        lan9303_tag[0] = htons(ETH_P_8021Q);
        lan9303_tag[1] = htons(tag);

        return skb;
}

static struct sk_buff *lan9303_rcv(struct sk_buff *skb, struct net_device *dev)
{
        u16 lan9303_tag1;
        unsigned int source_port;

        if (unlikely(!pskb_may_pull(skb, LAN9303_TAG_LEN))) {
                dev_warn_ratelimited(&dev->dev,
                                     "Dropping packet, cannot pull\n");
                return NULL;
        }

        if (skb_vlan_tag_present(skb)) {
                lan9303_tag1 = skb_vlan_tag_get(skb);
                __vlan_hwaccel_clear_tag(skb);
        } else {
                skb_push_rcsum(skb, ETH_HLEN);
                __skb_vlan_pop(skb, &lan9303_tag1);
                skb_pull_rcsum(skb, ETH_HLEN);
        }

        source_port = lan9303_tag1 & 0x3;

        skb->dev = dsa_conduit_find_user(dev, 0, source_port);
        if (!skb->dev) {
                dev_warn_ratelimited(&dev->dev, "Dropping packet due to invalid source port\n");
                return NULL;
        }

        if (!(lan9303_tag1 & LAN9303_TAG_RX_TRAPPED_TO_CPU))
                dsa_default_offload_fwd_mark(skb);

        return skb;
}

static const struct dsa_device_ops lan9303_netdev_ops = {
        .name = LAN9303_NAME,
        .proto  = DSA_TAG_PROTO_LAN9303,
        .xmit = lan9303_xmit,
        .rcv = lan9303_rcv,
        .needed_headroom = LAN9303_TAG_LEN,
};

MODULE_DESCRIPTION("DSA tag driver for SMSC/Microchip LAN9303 family of switches");
MODULE_LICENSE("GPL");
MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_LAN9303, LAN9303_NAME);

module_dsa_tag_driver(lan9303_netdev_ops);