// SPDX-License-Identifier: GPL-2.0-or-later
/* MHI Network driver - Network over MHI bus
 *
 * Copyright (C) 2020 Linaro Ltd <loic.poulain@linaro.org>
 */

#include <linux/if_arp.h>
#include <linux/mhi.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/skbuff.h>
#include <linux/u64_stats_sync.h>

#define MHI_NET_MIN_MTU         ETH_MIN_MTU
#define MHI_NET_MAX_MTU         0xffff
#define MHI_NET_DEFAULT_MTU     0x4000

struct mhi_net_stats {
        u64_stats_t rx_packets;
        u64_stats_t rx_bytes;
        u64_stats_t rx_errors;
        u64_stats_t tx_packets;
        u64_stats_t tx_bytes;
        u64_stats_t tx_errors;
        u64_stats_t tx_dropped;
        struct u64_stats_sync tx_syncp;
        struct u64_stats_sync rx_syncp;
};

struct mhi_net_dev {
        struct mhi_device *mdev;
        struct net_device *ndev;
        struct sk_buff *skbagg_head;
        struct sk_buff *skbagg_tail;
        struct delayed_work rx_refill;
        struct mhi_net_stats stats;
        u32 rx_queue_sz;
        int msg_enable;
        unsigned int mru;
};

struct mhi_device_info {
        const char *netname;
};

static int mhi_ndo_open(struct net_device *ndev)
{
        struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);

        /* Feed the rx buffer pool */
        schedule_delayed_work(&mhi_netdev->rx_refill, 0);

        /* Carrier is established via out-of-band channel (e.g. qmi) */
        netif_carrier_on(ndev);

        netif_start_queue(ndev);

        return 0;
}

static int mhi_ndo_stop(struct net_device *ndev)
{
        struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);

        netif_stop_queue(ndev);
        netif_carrier_off(ndev);
        cancel_delayed_work_sync(&mhi_netdev->rx_refill);

        return 0;
}

static netdev_tx_t mhi_ndo_xmit(struct sk_buff *skb, struct net_device *ndev)
{
        struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
        struct mhi_device *mdev = mhi_netdev->mdev;
        int err;

        err = mhi_queue_skb(mdev, DMA_TO_DEVICE, skb, skb->len, MHI_EOT);
        if (unlikely(err)) {
                net_err_ratelimited("%s: Failed to queue TX buf (%d)\n",
                                    ndev->name, err);
                dev_kfree_skb_any(skb);
                goto exit_drop;
        }

        if (mhi_queue_is_full(mdev, DMA_TO_DEVICE))
                netif_stop_queue(ndev);

        return NETDEV_TX_OK;

exit_drop:
        u64_stats_update_begin(&mhi_netdev->stats.tx_syncp);
        u64_stats_inc(&mhi_netdev->stats.tx_dropped);
        u64_stats_update_end(&mhi_netdev->stats.tx_syncp);

        return NETDEV_TX_OK;
}

static void mhi_ndo_get_stats64(struct net_device *ndev,
                                struct rtnl_link_stats64 *stats)
{
        struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
        unsigned int start;

        do {
                start = u64_stats_fetch_begin(&mhi_netdev->stats.rx_syncp);
                stats->rx_packets = u64_stats_read(&mhi_netdev->stats.rx_packets);
                stats->rx_bytes = u64_stats_read(&mhi_netdev->stats.rx_bytes);
                stats->rx_errors = u64_stats_read(&mhi_netdev->stats.rx_errors);
        } while (u64_stats_fetch_retry(&mhi_netdev->stats.rx_syncp, start));

        do {
                start = u64_stats_fetch_begin(&mhi_netdev->stats.tx_syncp);
                stats->tx_packets = u64_stats_read(&mhi_netdev->stats.tx_packets);
                stats->tx_bytes = u64_stats_read(&mhi_netdev->stats.tx_bytes);
                stats->tx_errors = u64_stats_read(&mhi_netdev->stats.tx_errors);
                stats->tx_dropped = u64_stats_read(&mhi_netdev->stats.tx_dropped);
        } while (u64_stats_fetch_retry(&mhi_netdev->stats.tx_syncp, start));
}

static const struct net_device_ops mhi_netdev_ops = {
        .ndo_open               = mhi_ndo_open,
        .ndo_stop               = mhi_ndo_stop,
        .ndo_start_xmit         = mhi_ndo_xmit,
        .ndo_get_stats64        = mhi_ndo_get_stats64,
};

static void mhi_net_setup(struct net_device *ndev)
{
        ndev->header_ops = NULL;  /* No header */
        ndev->type = ARPHRD_RAWIP;
        ndev->hard_header_len = 0;
        ndev->addr_len = 0;
        ndev->flags = IFF_POINTOPOINT | IFF_NOARP;
        ndev->netdev_ops = &mhi_netdev_ops;
        ndev->mtu = MHI_NET_DEFAULT_MTU;
        ndev->min_mtu = MHI_NET_MIN_MTU;
        ndev->max_mtu = MHI_NET_MAX_MTU;
        ndev->tx_queue_len = 1000;
}

static struct sk_buff *mhi_net_skb_agg(struct mhi_net_dev *mhi_netdev,
                                       struct sk_buff *skb)
{
        struct sk_buff *head = mhi_netdev->skbagg_head;
        struct sk_buff *tail = mhi_netdev->skbagg_tail;

        /* This is non-paged skb chaining using frag_list */
        if (!head) {
                mhi_netdev->skbagg_head = skb;
                return skb;
        }

        if (!skb_shinfo(head)->frag_list)
                skb_shinfo(head)->frag_list = skb;
        else
                tail->next = skb;

        head->len += skb->len;
        head->data_len += skb->len;
        head->truesize += skb->truesize;

        mhi_netdev->skbagg_tail = skb;

        return mhi_netdev->skbagg_head;
}

static void mhi_net_dl_callback(struct mhi_device *mhi_dev,
                                struct mhi_result *mhi_res)
{
        struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev->dev);
        struct sk_buff *skb = mhi_res->buf_addr;
        int free_desc_count;

        free_desc_count = mhi_get_free_desc_count(mhi_dev, DMA_FROM_DEVICE);

        if (unlikely(mhi_res->transaction_status)) {
                switch (mhi_res->transaction_status) {
                case -EOVERFLOW:
                        /* Packet can not fit in one MHI buffer and has been
                         * split over multiple MHI transfers, do re-aggregation.
                         * That usually means the device side MTU is larger than
                         * the host side MTU/MRU. Since this is not optimal,
                         * print a warning (once).
                         */
                        netdev_warn_once(mhi_netdev->ndev,
                                         "Fragmented packets received, fix MTU?\n");
                        skb_put(skb, mhi_res->bytes_xferd);
                        mhi_net_skb_agg(mhi_netdev, skb);
                        break;
                case -ENOTCONN:
                        /* MHI layer stopping/resetting the DL channel */
                        dev_kfree_skb_any(skb);
                        return;
                default:
                        /* Unknown error, simply drop */
                        dev_kfree_skb_any(skb);
                        u64_stats_update_begin(&mhi_netdev->stats.rx_syncp);
                        u64_stats_inc(&mhi_netdev->stats.rx_errors);
                        u64_stats_update_end(&mhi_netdev->stats.rx_syncp);
                }
        } else {
                skb_put(skb, mhi_res->bytes_xferd);

                if (mhi_netdev->skbagg_head) {
                        /* Aggregate the final fragment */
                        skb = mhi_net_skb_agg(mhi_netdev, skb);
                        mhi_netdev->skbagg_head = NULL;
                }

                switch (skb->data[0] & 0xf0) {
                case 0x40:
                        skb->protocol = htons(ETH_P_IP);
                        break;
                case 0x60:
                        skb->protocol = htons(ETH_P_IPV6);
                        break;
                default:
                        skb->protocol = htons(ETH_P_MAP);
                        break;
                }

                u64_stats_update_begin(&mhi_netdev->stats.rx_syncp);
                u64_stats_inc(&mhi_netdev->stats.rx_packets);
                u64_stats_add(&mhi_netdev->stats.rx_bytes, skb->len);
                u64_stats_update_end(&mhi_netdev->stats.rx_syncp);
                __netif_rx(skb);
        }

        /* Refill if RX buffers queue becomes low */
        if (free_desc_count >= mhi_netdev->rx_queue_sz / 2)
                schedule_delayed_work(&mhi_netdev->rx_refill, 0);
}

static void mhi_net_ul_callback(struct mhi_device *mhi_dev,
                                struct mhi_result *mhi_res)
{
        struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev->dev);
        struct net_device *ndev = mhi_netdev->ndev;
        struct mhi_device *mdev = mhi_netdev->mdev;
        struct sk_buff *skb = mhi_res->buf_addr;

        /* Hardware has consumed the buffer, so free the skb (which is not
         * freed by the MHI stack) and perform accounting.
         */
        dev_consume_skb_any(skb);

        u64_stats_update_begin(&mhi_netdev->stats.tx_syncp);
        if (unlikely(mhi_res->transaction_status)) {
                /* MHI layer stopping/resetting the UL channel */
                if (mhi_res->transaction_status == -ENOTCONN) {
                        u64_stats_update_end(&mhi_netdev->stats.tx_syncp);
                        return;
                }

                u64_stats_inc(&mhi_netdev->stats.tx_errors);
        } else {
                u64_stats_inc(&mhi_netdev->stats.tx_packets);
                u64_stats_add(&mhi_netdev->stats.tx_bytes, mhi_res->bytes_xferd);
        }
        u64_stats_update_end(&mhi_netdev->stats.tx_syncp);

        if (netif_queue_stopped(ndev) && !mhi_queue_is_full(mdev, DMA_TO_DEVICE))
                netif_wake_queue(ndev);
}

static void mhi_net_rx_refill_work(struct work_struct *work)
{
        struct mhi_net_dev *mhi_netdev = container_of(work, struct mhi_net_dev,
                                                      rx_refill.work);
        struct net_device *ndev = mhi_netdev->ndev;
        struct mhi_device *mdev = mhi_netdev->mdev;
        struct sk_buff *skb;
        unsigned int size;
        int err;

        size = mhi_netdev->mru ? mhi_netdev->mru : READ_ONCE(ndev->mtu);

        while (!mhi_queue_is_full(mdev, DMA_FROM_DEVICE)) {
                skb = netdev_alloc_skb(ndev, size);
                if (unlikely(!skb))
                        break;

                err = mhi_queue_skb(mdev, DMA_FROM_DEVICE, skb, size, MHI_EOT);
                if (unlikely(err)) {
                        net_err_ratelimited("%s: Failed to queue RX buf (%d)\n",
                                            ndev->name, err);
                        kfree_skb(skb);
                        break;
                }

                /* Do not hog the CPU if rx buffers are consumed faster than
                 * queued (unlikely).
                 */
                cond_resched();
        }

        /* If we're still starved of rx buffers, reschedule later */
        if (mhi_get_free_desc_count(mdev, DMA_FROM_DEVICE) == mhi_netdev->rx_queue_sz)
                schedule_delayed_work(&mhi_netdev->rx_refill, HZ / 2);
}

static int mhi_net_newlink(struct mhi_device *mhi_dev, struct net_device *ndev)
{
        struct mhi_net_dev *mhi_netdev;
        int err;

        mhi_netdev = netdev_priv(ndev);

        dev_set_drvdata(&mhi_dev->dev, mhi_netdev);
        mhi_netdev->ndev = ndev;
        mhi_netdev->mdev = mhi_dev;
        mhi_netdev->skbagg_head = NULL;
        mhi_netdev->mru = mhi_dev->mhi_cntrl->mru;

        INIT_DELAYED_WORK(&mhi_netdev->rx_refill, mhi_net_rx_refill_work);
        u64_stats_init(&mhi_netdev->stats.rx_syncp);
        u64_stats_init(&mhi_netdev->stats.tx_syncp);

        /* Start MHI channels */
        err = mhi_prepare_for_transfer(mhi_dev);
        if (err)
                return err;

        /* Number of transfer descriptors determines size of the queue */
        mhi_netdev->rx_queue_sz = mhi_get_free_desc_count(mhi_dev, DMA_FROM_DEVICE);

        err = register_netdev(ndev);
        if (err)
                return err;

        return 0;
}

static void mhi_net_dellink(struct mhi_device *mhi_dev, struct net_device *ndev)
{
        struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);

        unregister_netdev(ndev);

        mhi_unprepare_from_transfer(mhi_dev);

        kfree_skb(mhi_netdev->skbagg_head);

        free_netdev(ndev);

        dev_set_drvdata(&mhi_dev->dev, NULL);
}

static int mhi_net_probe(struct mhi_device *mhi_dev,
                         const struct mhi_device_id *id)
{
        const struct mhi_device_info *info = (struct mhi_device_info *)id->driver_data;
        struct net_device *ndev;
        int err;

        ndev = alloc_netdev(sizeof(struct mhi_net_dev), info->netname,
                            NET_NAME_PREDICTABLE, mhi_net_setup);
        if (!ndev)
                return -ENOMEM;

        SET_NETDEV_DEV(ndev, &mhi_dev->dev);

        err = mhi_net_newlink(mhi_dev, ndev);
        if (err) {
                free_netdev(ndev);
                return err;
        }

        return 0;
}

static void mhi_net_remove(struct mhi_device *mhi_dev)
{
        struct mhi_net_dev *mhi_netdev = dev_get_drvdata(&mhi_dev->dev);

        mhi_net_dellink(mhi_dev, mhi_netdev->ndev);
}

static const struct mhi_device_info mhi_hwip0 = {
        .netname = "mhi_hwip%d",
};

static const struct mhi_device_info mhi_swip0 = {
        .netname = "mhi_swip%d",
};

static const struct mhi_device_id mhi_net_id_table[] = {
        /* Hardware accelerated data PATH (to modem IPA), protocol agnostic */
        { .chan = "IP_HW0", .driver_data = (kernel_ulong_t)&mhi_hwip0 },
        /* Software data PATH (to modem CPU) */
        { .chan = "IP_SW0", .driver_data = (kernel_ulong_t)&mhi_swip0 },
        {}
};
MODULE_DEVICE_TABLE(mhi, mhi_net_id_table);

static struct mhi_driver mhi_net_driver = {
        .probe = mhi_net_probe,
        .remove = mhi_net_remove,
        .dl_xfer_cb = mhi_net_dl_callback,
        .ul_xfer_cb = mhi_net_ul_callback,
        .id_table = mhi_net_id_table,
        .driver = {
                .name = "mhi_net",
        },
};

module_mhi_driver(mhi_net_driver);

MODULE_AUTHOR("Loic Poulain <loic.poulain@linaro.org>");
MODULE_DESCRIPTION("Network over MHI");
MODULE_LICENSE("GPL v2");