// SPDX-License-Identifier: GPL-2.0
/* Copyright (c) 2019, Vladimir Oltean <olteanv@gmail.com>
 */
#include <linux/if_vlan.h>
#include <linux/dsa/sja1105.h>
#include <linux/dsa/8021q.h>
#include <linux/packing.h>
#include "dsa_priv.h"

/* Similar to is_link_local_ether_addr(hdr->h_dest) but also covers PTP */
static inline bool sja1105_is_link_local(const struct sk_buff *skb)
{
        const struct ethhdr *hdr = eth_hdr(skb);
        u64 dmac = ether_addr_to_u64(hdr->h_dest);

        if (ntohs(hdr->h_proto) == ETH_P_SJA1105_META)
                return false;
        if ((dmac & SJA1105_LINKLOCAL_FILTER_A_MASK) ==
                    SJA1105_LINKLOCAL_FILTER_A)
                return true;
        if ((dmac & SJA1105_LINKLOCAL_FILTER_B_MASK) ==
                    SJA1105_LINKLOCAL_FILTER_B)
                return true;
        return false;
}

struct sja1105_meta {
        u64 tstamp;
        u64 dmac_byte_4;
        u64 dmac_byte_3;
        u64 source_port;
        u64 switch_id;
};

static void sja1105_meta_unpack(const struct sk_buff *skb,
                                struct sja1105_meta *meta)
{
        u8 *buf = skb_mac_header(skb) + ETH_HLEN;

        /* UM10944.pdf section 4.2.17 AVB Parameters:
         * Structure of the meta-data follow-up frame.
         * It is in network byte order, so there are no quirks
         * while unpacking the meta frame.
         *
         * Also SJA1105 E/T only populates bits 23:0 of the timestamp
         * whereas P/Q/R/S does 32 bits. Since the structure is the
         * same and the E/T puts zeroes in the high-order byte, use
         * a unified unpacking command for both device series.
         */
        packing(buf,     &meta->tstamp,     31, 0, 4, UNPACK, 0);
        packing(buf + 4, &meta->dmac_byte_4, 7, 0, 1, UNPACK, 0);
        packing(buf + 5, &meta->dmac_byte_3, 7, 0, 1, UNPACK, 0);
        packing(buf + 6, &meta->source_port, 7, 0, 1, UNPACK, 0);
        packing(buf + 7, &meta->switch_id,   7, 0, 1, UNPACK, 0);
}

static inline bool sja1105_is_meta_frame(const struct sk_buff *skb)
{
        const struct ethhdr *hdr = eth_hdr(skb);
        u64 smac = ether_addr_to_u64(hdr->h_source);
        u64 dmac = ether_addr_to_u64(hdr->h_dest);

        if (smac != SJA1105_META_SMAC)
                return false;
        if (dmac != SJA1105_META_DMAC)
                return false;
        if (ntohs(hdr->h_proto) != ETH_P_SJA1105_META)
                return false;
        return true;
}

/* This is the first time the tagger sees the frame on RX.
 * Figure out if we can decode it.
 */
static bool sja1105_filter(const struct sk_buff *skb, struct net_device *dev)
{
        if (!dsa_port_is_vlan_filtering(dev->dsa_ptr))
                return true;
        if (sja1105_is_link_local(skb))
                return true;
        if (sja1105_is_meta_frame(skb))
                return true;
        return false;
}

/* Calls sja1105_port_deferred_xmit in sja1105_main.c */
static struct sk_buff *sja1105_defer_xmit(struct sja1105_port *sp,
                                          struct sk_buff *skb)
{
        /* Increase refcount so the kfree_skb in dsa_slave_xmit
         * won't really free the packet.
         */
        skb_queue_tail(&sp->xmit_queue, skb_get(skb));
        kthread_queue_work(sp->xmit_worker, &sp->xmit_work);

        return NULL;
}

static struct sk_buff *sja1105_xmit(struct sk_buff *skb,
                                    struct net_device *netdev)
{
        struct dsa_port *dp = dsa_slave_to_port(netdev);
        u16 tx_vid = dsa_8021q_tx_vid(dp->ds, dp->index);
        u16 queue_mapping = skb_get_queue_mapping(skb);
        u8 pcp = netdev_txq_to_tc(netdev, queue_mapping);

        /* Transmitting management traffic does not rely upon switch tagging,
         * but instead SPI-installed management routes. Part 2 of this
         * is the .port_deferred_xmit driver callback.
         */
        if (unlikely(sja1105_is_link_local(skb)))
                return sja1105_defer_xmit(dp->priv, skb);

        /* If we are under a vlan_filtering bridge, IP termination on
         * switch ports based on 802.1Q tags is simply too brittle to
         * be passable. So just defer to the dsa_slave_notag_xmit
         * implementation.
         */
        if (dsa_port_is_vlan_filtering(dp))
                return skb;

        return dsa_8021q_xmit(skb, netdev, ETH_P_SJA1105,
                             ((pcp << VLAN_PRIO_SHIFT) | tx_vid));
}

static void sja1105_transfer_meta(struct sk_buff *skb,
                                  const struct sja1105_meta *meta)
{
        struct ethhdr *hdr = eth_hdr(skb);

        hdr->h_dest[3] = meta->dmac_byte_3;
        hdr->h_dest[4] = meta->dmac_byte_4;
        SJA1105_SKB_CB(skb)->meta_tstamp = meta->tstamp;
}

/* This is a simple state machine which follows the hardware mechanism of
 * generating RX timestamps:
 *
 * After each timestampable skb (all traffic for which send_meta1 and
 * send_meta0 is true, aka all MAC-filtered link-local traffic) a meta frame
 * containing a partial timestamp is immediately generated by the switch and
 * sent as a follow-up to the link-local frame on the CPU port.
 *
 * The meta frames have no unique identifier (such as sequence number) by which
 * one may pair them to the correct timestampable frame.
 * Instead, the switch has internal logic that ensures no frames are sent on
 * the CPU port between a link-local timestampable frame and its corresponding
 * meta follow-up. It also ensures strict ordering between ports (lower ports
 * have higher priority towards the CPU port). For this reason, a per-port
 * data structure is not needed/desirable.
 *
 * This function pairs the link-local frame with its partial timestamp from the
 * meta follow-up frame. The full timestamp will be reconstructed later in a
 * work queue.
 */
static struct sk_buff
*sja1105_rcv_meta_state_machine(struct sk_buff *skb,
                                struct sja1105_meta *meta,
                                bool is_link_local,
                                bool is_meta)
{
        struct sja1105_port *sp;
        struct dsa_port *dp;

        dp = dsa_slave_to_port(skb->dev);
        sp = dp->priv;

        /* Step 1: A timestampable frame was received.
         * Buffer it until we get its meta frame.
         */
        if (is_link_local) {
                if (!test_bit(SJA1105_HWTS_RX_EN, &sp->data->state))
                        /* Do normal processing. */
                        return skb;

                spin_lock(&sp->data->meta_lock);
                /* Was this a link-local frame instead of the meta
                 * that we were expecting?
                 */
                if (sp->data->stampable_skb) {
                        dev_err_ratelimited(dp->ds->dev,
                                            "Expected meta frame, is %12llx "
                                            "in the DSA master multicast filter?\n",
                                            SJA1105_META_DMAC);
                        kfree_skb(sp->data->stampable_skb);
                }

                /* Hold a reference to avoid dsa_switch_rcv
                 * from freeing the skb.
                 */
                sp->data->stampable_skb = skb_get(skb);
                spin_unlock(&sp->data->meta_lock);

                /* Tell DSA we got nothing */
                return NULL;

        /* Step 2: The meta frame arrived.
         * Time to take the stampable skb out of the closet, annotate it
         * with the partial timestamp, and pretend that we received it
         * just now (basically masquerade the buffered frame as the meta
         * frame, which serves no further purpose).
         */
        } else if (is_meta) {
                struct sk_buff *stampable_skb;

                /* Drop the meta frame if we're not in the right state
                 * to process it.
                 */
                if (!test_bit(SJA1105_HWTS_RX_EN, &sp->data->state))
                        return NULL;

                spin_lock(&sp->data->meta_lock);

                stampable_skb = sp->data->stampable_skb;
                sp->data->stampable_skb = NULL;

                /* Was this a meta frame instead of the link-local
                 * that we were expecting?
                 */
                if (!stampable_skb) {
                        dev_err_ratelimited(dp->ds->dev,
                                            "Unexpected meta frame\n");
                        spin_unlock(&sp->data->meta_lock);
                        return NULL;
                }

                if (stampable_skb->dev != skb->dev) {
                        dev_err_ratelimited(dp->ds->dev,
                                            "Meta frame on wrong port\n");
                        spin_unlock(&sp->data->meta_lock);
                        return NULL;
                }

                /* Free the meta frame and give DSA the buffered stampable_skb
                 * for further processing up the network stack.
                 */
                kfree_skb(skb);
                skb = stampable_skb;
                sja1105_transfer_meta(skb, meta);

                spin_unlock(&sp->data->meta_lock);
        }

        return skb;
}

static struct sk_buff *sja1105_rcv(struct sk_buff *skb,
                                   struct net_device *netdev,
                                   struct packet_type *pt)
{
        struct sja1105_meta meta = {0};
        int source_port, switch_id;
        struct ethhdr *hdr;
        u16 tpid, vid, tci;
        bool is_link_local;
        bool is_tagged;
        bool is_meta;

        hdr = eth_hdr(skb);
        tpid = ntohs(hdr->h_proto);
        is_tagged = (tpid == ETH_P_SJA1105);
        is_link_local = sja1105_is_link_local(skb);
        is_meta = sja1105_is_meta_frame(skb);

        skb->offload_fwd_mark = 1;

        if (is_tagged) {
                /* Normal traffic path. */
                skb_push_rcsum(skb, ETH_HLEN);
                __skb_vlan_pop(skb, &tci);
                skb_pull_rcsum(skb, ETH_HLEN);
                skb_reset_network_header(skb);
                skb_reset_transport_header(skb);

                vid = tci & VLAN_VID_MASK;
                source_port = dsa_8021q_rx_source_port(vid);
                switch_id = dsa_8021q_rx_switch_id(vid);
                skb->priority = (tci & VLAN_PRIO_MASK) >> VLAN_PRIO_SHIFT;
        } else if (is_link_local) {
                /* Management traffic path. Switch embeds the switch ID and
                 * port ID into bytes of the destination MAC, courtesy of
                 * the incl_srcpt options.
                 */
                source_port = hdr->h_dest[3];
                switch_id = hdr->h_dest[4];
                /* Clear the DMAC bytes that were mangled by the switch */
                hdr->h_dest[3] = 0;
                hdr->h_dest[4] = 0;
        } else if (is_meta) {
                sja1105_meta_unpack(skb, &meta);
                source_port = meta.source_port;
                switch_id = meta.switch_id;
        } else {
                return NULL;
        }

        skb->dev = dsa_master_find_slave(netdev, switch_id, source_port);
        if (!skb->dev) {
                netdev_warn(netdev, "Couldn't decode source port\n");
                return NULL;
        }

        return sja1105_rcv_meta_state_machine(skb, &meta, is_link_local,
                                              is_meta);
}

static struct dsa_device_ops sja1105_netdev_ops = {
        .name = "sja1105",
        .proto = DSA_TAG_PROTO_SJA1105,
        .xmit = sja1105_xmit,
        .rcv = sja1105_rcv,
        .filter = sja1105_filter,
        .overhead = VLAN_HLEN,
};

MODULE_LICENSE("GPL v2");
MODULE_ALIAS_DSA_TAG_DRIVER(DSA_TAG_PROTO_SJA1105);

module_dsa_tag_driver(sja1105_netdev_ops);