// 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/kthread.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

#define RX_FEFILL_LVL	50 /* Refill the RX queue if lower than 50% */

struct mhi_net_stats {
	u64_stats_t rx_packets;
	u64_stats_t rx_bytes;
	u64_stats_t rx_errors;
	u64_stats_t rx_dropped;
	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 task_struct *refill_task;
	u32 rx_queue_sz;
	u32 refill_level;
	struct mhi_net_stats stats;
	wait_queue_head_t refill_wq;
};

static int mhi_net_refill_thread(void *data)
{
	struct mhi_net_dev *mhi_netdev = data;
	struct net_device *ndev = mhi_netdev->ndev;
	struct mhi_device *mdev = mhi_netdev->mdev;
	int size = READ_ONCE(ndev->mtu);
	struct sk_buff *skb;
	int err;

	while (1) {
		err = wait_event_interruptible(mhi_netdev->refill_wq,
					       !mhi_queue_is_full(mdev, DMA_FROM_DEVICE)
					       || kthread_should_stop());
		if (err || kthread_should_stop())
			break;

		skb = netdev_alloc_skb(ndev, size);
		if (unlikely(!skb)) {
			/* No memory, retry later */
			net_warn_ratelimited("%s: Unable to allocate RX buf\n",
					     ndev->name);
			schedule_timeout_interruptible(msecs_to_jiffies(250));
			continue;
		}

		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);
		}

		/* Do not hog the CPU */
		cond_resched();
	}

	return 0;
}

static int mhi_ndo_open(struct net_device *ndev)
{
	struct mhi_net_dev *mhi_netdev = netdev_priv(ndev);
	unsigned int qsz = mhi_netdev->rx_queue_sz;

	/* Feed the rx buffer pool */
	mhi_netdev->refill_level = qsz - qsz * RX_FEFILL_LVL / 100;

	mhi_netdev->refill_task = kthread_run(mhi_net_refill_thread, mhi_netdev,
					      "mhi-net-rx");
	if (IS_ERR(mhi_netdev->refill_task))
		return PTR_ERR(mhi_netdev->refill_task);

	/* 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);

	kthread_stop(mhi_netdev->refill_task);
	netif_stop_queue(ndev);
	netif_carrier_off(ndev);

	return 0;
}

static int 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);

		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);

		/* drop the packet */
		dev_kfree_skb_any(skb);
	}

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

	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_irq(&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);
		stats->rx_dropped = u64_stats_read(&mhi_netdev->stats.rx_dropped);
	} while (u64_stats_fetch_retry_irq(&mhi_netdev->stats.rx_syncp, start));

	do {
		start = u64_stats_fetch_begin_irq(&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_irq(&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;

	/* data_len is normally the size of paged data, in our case there is no
	 * paged data (nr_frags = 0), so it represents the size of chained skbs,
	 * This way, net core will consider skb->frag_list.
	 */
	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;

	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;
		}

		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);

		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;
		}

		netif_rx(skb);
	}

	/* Refill if RX buffers queue becomes low */
	if (mhi_get_free_desc_count(mhi_dev, DMA_FROM_DEVICE) >= mhi_netdev->refill_level)
		wake_up_interruptible(&mhi_netdev->refill_wq);
}

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 struct device_type wwan_type = {
	.name = "wwan",
};

static int mhi_net_probe(struct mhi_device *mhi_dev,
			 const struct mhi_device_id *id)
{
	const char *netname = (char *)id->driver_data;
	struct device *dev = &mhi_dev->dev;
	struct mhi_net_dev *mhi_netdev;
	struct net_device *ndev;
	int err;

	ndev = alloc_netdev(sizeof(*mhi_netdev), netname, NET_NAME_PREDICTABLE,
			    mhi_net_setup);
	if (!ndev)
		return -ENOMEM;

	mhi_netdev = netdev_priv(ndev);
	dev_set_drvdata(dev, mhi_netdev);
	mhi_netdev->ndev = ndev;
	mhi_netdev->mdev = mhi_dev;
	mhi_netdev->skbagg_head = NULL;
	SET_NETDEV_DEV(ndev, &mhi_dev->dev);
	SET_NETDEV_DEVTYPE(ndev, &wwan_type);

	init_waitqueue_head(&mhi_netdev->refill_wq);
	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, 0);
	if (err)
		goto out_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)
		goto out_err;

	return 0;

out_err:
	free_netdev(ndev);
	return err;
}

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

	unregister_netdev(mhi_netdev->ndev);

	mhi_unprepare_from_transfer(mhi_netdev->mdev);

	if (mhi_netdev->skbagg_head)
		kfree_skb(mhi_netdev->skbagg_head);

	free_netdev(mhi_netdev->ndev);
}

static const struct mhi_device_id mhi_net_id_table[] = {
	{ .chan = "IP_HW0", .driver_data = (kernel_ulong_t)"mhi_hwip%d" },
	{ .chan = "IP_SW0", .driver_data = (kernel_ulong_t)"mhi_swip%d" },
	{}
};
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",
		.owner = THIS_MODULE,
	},
};

module_mhi_driver(mhi_net_driver);

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