// SPDX-License-Identifier: GPL-2.0+
/*
 * DSA driver Special Tag support for MaxLinear GSW1xx switch chips
 *
 * Copyright (C) 2025 Daniel Golle <daniel@makrotopia.org>
 * Copyright (C) 2023 - 2024 MaxLinear Inc.
 */

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

#include "tag.h"

/* To define the outgoing port and to discover the incoming port a special
 * tag is used by the GSW1xx.
 *
 *       Dest MAC       Src MAC    special TAG        EtherType
 * ...| 1 2 3 4 5 6 | 1 2 3 4 5 6 | 1 2 3 4 5 6 7 8 | 1 2 |...
 *                                |<--------------->|
 */

#define GSW1XX_TAG_NAME         "gsw1xx"

/* special tag header length (RX and TX) */
#define GSW1XX_HEADER_LEN               8

/* Word 0 = Ethertype -> 0x88C3 */

/* Word 1 */
#define GSW1XX_TX_PORT_MAP              GENMASK(7, 0)
#define GSW1XX_TX_PORT_MAP_EN           BIT(15)
#define GSW1XX_TX_CLASS_EN              BIT(14)
#define GSW1XX_TX_TIME_STAMP_EN         BIT(13)
#define GSW1XX_TX_LRN_DIS               BIT(12)
#define GSW1XX_TX_CLASS                 GENMASK(11, 8)

/* special tag in RX path header */
/* Word 2 */
#define GSW1XX_RX_PORT_MAP              GENMASK(15, 8)

static struct sk_buff *gsw1xx_tag_xmit(struct sk_buff *skb,
                                       struct net_device *dev)
{
        __be16 *gsw1xx_tag;
        u16 tag;

        /* provide additional space 'GSW1XX_HEADER_LEN' bytes */
        skb_push(skb, GSW1XX_HEADER_LEN);

        /* add space between MAC address and Ethertype */
        dsa_alloc_etype_header(skb, GSW1XX_HEADER_LEN);

        /* special tag ingress */
        gsw1xx_tag = dsa_etype_header_pos_tx(skb);
        gsw1xx_tag[0] = htons(ETH_P_MXLGSW);

        tag = FIELD_PREP(GSW1XX_TX_PORT_MAP, dsa_xmit_port_mask(skb, dev)) |
              GSW1XX_TX_PORT_MAP_EN | GSW1XX_TX_LRN_DIS;
        gsw1xx_tag[1] = htons(tag);
        gsw1xx_tag[2] = 0;
        gsw1xx_tag[3] = 0;

        return skb;
}

static struct sk_buff *gsw1xx_tag_rcv(struct sk_buff *skb,
                                      struct net_device *dev)
{
        int port;
        __be16 *gsw1xx_tag;

        if (unlikely(!pskb_may_pull(skb, GSW1XX_HEADER_LEN))) {
                dev_warn_ratelimited(&dev->dev, "Dropping packet, cannot pull SKB\n");
                kfree_skb(skb);
                return NULL;
        }

        gsw1xx_tag = dsa_etype_header_pos_rx(skb);

        if (unlikely(ntohs(gsw1xx_tag[0]) != ETH_P_MXLGSW)) {
                dev_warn_ratelimited(&dev->dev, "Dropping packet due to invalid special tag\n");
                dev_warn_ratelimited(&dev->dev, "Tag: %8ph\n", gsw1xx_tag);
                kfree_skb(skb);
                return NULL;
        }

        /* Get source port information */
        port = FIELD_GET(GSW1XX_RX_PORT_MAP, ntohs(gsw1xx_tag[1]));
        skb->dev = dsa_conduit_find_user(dev, 0, port);
        if (!skb->dev) {
                dev_warn_ratelimited(&dev->dev, "Dropping packet due to invalid source port\n");
                dev_warn_ratelimited(&dev->dev, "Tag: %8ph\n", gsw1xx_tag);
                kfree_skb(skb);
                return NULL;
        }

        /* remove the GSW1xx special tag between MAC addresses and the current
         * ethertype field.
         */
        skb_pull_rcsum(skb, GSW1XX_HEADER_LEN);
        dsa_strip_etype_header(skb, GSW1XX_HEADER_LEN);

        return skb;
}

static const struct dsa_device_ops gsw1xx_netdev_ops = {
        .name                   = GSW1XX_TAG_NAME,
        .proto                  = DSA_TAG_PROTO_MXL_GSW1XX,
        .xmit                   = gsw1xx_tag_xmit,
        .rcv                    = gsw1xx_tag_rcv,
        .needed_headroom        = GSW1XX_HEADER_LEN,
};

MODULE_DESCRIPTION("DSA tag driver for MaxLinear GSW1xx 8 byte protocol");
MODULE_LICENSE("GPL");
MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_MXL_GSW1XX, GSW1XX_TAG_NAME);

module_dsa_tag_driver(gsw1xx_netdev_ops);