// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * DSA Special Tag for MaxLinear 862xx switch chips
 *
 * Copyright (C) 2025 Daniel Golle <daniel@makrotopia.org>
 * Copyright (C) 2024 MaxLinear Inc.
 */

#include <linux/bitops.h>
#include <linux/etherdevice.h>
#include <linux/skbuff.h>
#include <net/dsa.h>
#include "tag.h"

#define MXL862_NAME     "mxl862xx"

#define MXL862_HEADER_LEN       8

/* Word 0 -> EtherType */

/* Word 2 */
#define MXL862_SUBIF_ID         GENMASK(4, 0)

/* Word 3 */
#define MXL862_IGP_EGP          GENMASK(3, 0)

static struct sk_buff *mxl862_tag_xmit(struct sk_buff *skb,
                                       struct net_device *dev)
{
        struct dsa_port *dp = dsa_user_to_port(dev);
        struct dsa_port *cpu_dp = dp->cpu_dp;
        unsigned int cpu_port, sub_interface;
        __be16 *mxl862_tag;

        cpu_port = cpu_dp->index;

        /* target port sub-interface ID relative to the CPU port */
        sub_interface = dp->index + 16 - cpu_port;

        /* provide additional space 'MXL862_HEADER_LEN' bytes */
        skb_push(skb, MXL862_HEADER_LEN);

        /* shift MAC address to the beginning of the enlarged buffer,
         * releasing the space required for DSA tag (between MAC address and
         * Ethertype)
         */
        dsa_alloc_etype_header(skb, MXL862_HEADER_LEN);

        /* special tag ingress (from the perspective of the switch) */
        mxl862_tag = dsa_etype_header_pos_tx(skb);
        mxl862_tag[0] = htons(ETH_P_MXLGSW);
        mxl862_tag[1] = 0;
        mxl862_tag[2] = htons(FIELD_PREP(MXL862_SUBIF_ID, sub_interface));
        mxl862_tag[3] = htons(FIELD_PREP(MXL862_IGP_EGP, cpu_port));

        return skb;
}

static struct sk_buff *mxl862_tag_rcv(struct sk_buff *skb,
                                      struct net_device *dev)
{
        __be16 *mxl862_tag;
        int port;

        if (unlikely(!pskb_may_pull(skb, MXL862_HEADER_LEN))) {
                dev_warn_ratelimited(&dev->dev, "Cannot pull SKB, packet dropped\n");
                return NULL;
        }

        mxl862_tag = dsa_etype_header_pos_rx(skb);

        if (unlikely(mxl862_tag[0] != htons(ETH_P_MXLGSW))) {
                dev_warn_ratelimited(&dev->dev,
                                     "Invalid special tag marker, packet dropped, tag: %8ph\n",
                                     mxl862_tag);
                return NULL;
        }

        /* Get source port information */
        port = FIELD_GET(MXL862_IGP_EGP, ntohs(mxl862_tag[3]));
        skb->dev = dsa_conduit_find_user(dev, 0, port);
        if (unlikely(!skb->dev)) {
                dev_warn_ratelimited(&dev->dev,
                                     "Invalid source port, packet dropped, tag: %8ph\n",
                                     mxl862_tag);
                return NULL;
        }

        /* remove the MxL862xx special tag between the MAC addresses and the
         * current ethertype field.
         */
        skb_pull_rcsum(skb, MXL862_HEADER_LEN);
        dsa_strip_etype_header(skb, MXL862_HEADER_LEN);

        return skb;
}

static const struct dsa_device_ops mxl862_netdev_ops = {
        .name = MXL862_NAME,
        .proto = DSA_TAG_PROTO_MXL862,
        .xmit = mxl862_tag_xmit,
        .rcv = mxl862_tag_rcv,
        .needed_headroom = MXL862_HEADER_LEN,
};

MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_MXL862, MXL862_NAME);
MODULE_DESCRIPTION("DSA tag driver for MaxLinear MxL862xx switches");
MODULE_LICENSE("GPL");

module_dsa_tag_driver(mxl862_netdev_ops);