// SPDX-License-Identifier: GPL-2.0
/*
 * Handler for Realtek 4 byte DSA switch tags
 * Currently only supports protocol "A" found in RTL8366RB
 * Copyright (c) 2020 Linus Walleij <linus.walleij@linaro.org>
 *
 * This "proprietary tag" header looks like so:
 *
 * -------------------------------------------------
 * | MAC DA | MAC SA | 0x8899 | 2 bytes tag | Type |
 * -------------------------------------------------
 *
 * The 2 bytes tag form a 16 bit big endian word. The exact
 * meaning has been guessed from packet dumps from ingress
 * frames.
 */

#include <linux/etherdevice.h>
#include <linux/bits.h>

#include "tag.h"

#define RTL4_A_NAME             "rtl4a"

#define RTL4_A_HDR_LEN          4
#define RTL4_A_PROTOCOL_SHIFT   12
/*
 * 0x1 = Realtek Remote Control protocol (RRCP)
 * 0x2/0x3 seems to be used for loopback testing
 * 0x9 = RTL8306 DSA protocol
 * 0xa = RTL8366RB DSA protocol
 */
#define RTL4_A_PROTOCOL_RTL8366RB       0xa

static struct sk_buff *rtl4a_tag_xmit(struct sk_buff *skb,
                                      struct net_device *dev)
{
        struct dsa_port *dp = dsa_user_to_port(dev);
        __be16 *p;
        u8 *tag;
        u16 out;

        /* Pad out to at least 60 bytes */
        if (unlikely(__skb_put_padto(skb, ETH_ZLEN, false)))
                return NULL;

        netdev_dbg(dev, "add realtek tag to package to port %d\n",
                   dp->index);
        skb_push(skb, RTL4_A_HDR_LEN);

        dsa_alloc_etype_header(skb, RTL4_A_HDR_LEN);
        tag = dsa_etype_header_pos_tx(skb);

        /* Set Ethertype */
        p = (__be16 *)tag;
        *p = htons(ETH_P_REALTEK);

        out = (RTL4_A_PROTOCOL_RTL8366RB << RTL4_A_PROTOCOL_SHIFT);
        /* The lower bits indicate the port number */
        out |= dsa_xmit_port_mask(skb, dev);

        p = (__be16 *)(tag + 2);
        *p = htons(out);

        return skb;
}

static struct sk_buff *rtl4a_tag_rcv(struct sk_buff *skb,
                                     struct net_device *dev)
{
        u16 protport;
        __be16 *p;
        u16 etype;
        u8 *tag;
        u8 prot;
        u8 port;

        if (unlikely(!pskb_may_pull(skb, RTL4_A_HDR_LEN)))
                return NULL;

        tag = dsa_etype_header_pos_rx(skb);
        p = (__be16 *)tag;
        etype = ntohs(*p);
        if (etype != ETH_P_REALTEK) {
                /* Not custom, just pass through */
                netdev_dbg(dev, "non-realtek ethertype 0x%04x\n", etype);
                return skb;
        }
        p = (__be16 *)(tag + 2);
        protport = ntohs(*p);
        /* The 4 upper bits are the protocol */
        prot = (protport >> RTL4_A_PROTOCOL_SHIFT) & 0x0f;
        if (prot != RTL4_A_PROTOCOL_RTL8366RB) {
                netdev_err(dev, "unknown realtek protocol 0x%01x\n", prot);
                return NULL;
        }
        port = protport & 0xff;

        skb->dev = dsa_conduit_find_user(dev, 0, port);
        if (!skb->dev) {
                netdev_dbg(dev, "could not find user for port %d\n", port);
                return NULL;
        }

        /* Remove RTL4 tag and recalculate checksum */
        skb_pull_rcsum(skb, RTL4_A_HDR_LEN);

        dsa_strip_etype_header(skb, RTL4_A_HDR_LEN);

        dsa_default_offload_fwd_mark(skb);

        return skb;
}

static const struct dsa_device_ops rtl4a_netdev_ops = {
        .name   = RTL4_A_NAME,
        .proto  = DSA_TAG_PROTO_RTL4_A,
        .xmit   = rtl4a_tag_xmit,
        .rcv    = rtl4a_tag_rcv,
        .needed_headroom = RTL4_A_HDR_LEN,
};
module_dsa_tag_driver(rtl4a_netdev_ops);

MODULE_DESCRIPTION("DSA tag driver for Realtek 4 byte protocol A tags");
MODULE_LICENSE("GPL");
MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_RTL4_A, RTL4_A_NAME);