// SPDX-License-Identifier: GPL-2.0
/*
 * Implements DMTF specification
 * "DSP0233 Management Component Transport Protocol (MCTP) I3C Transport
 * Binding"
 * https://www.dmtf.org/sites/default/files/standards/documents/DSP0233_1.0.0.pdf
 *
 * Copyright (c) 2023 Code Construct
 */

#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/i3c/device.h>
#include <linux/i3c/master.h>
#include <linux/if_arp.h>
#include <linux/unaligned.h>
#include <net/mctp.h>
#include <net/mctpdevice.h>

#define MCTP_I3C_MAXBUF 65536
/* 48 bit Provisioned Id */
#define PID_SIZE 6

/* 64 byte payload, 4 byte MCTP header */
static const int MCTP_I3C_MINMTU = 64 + 4;
/* One byte less to allow for the PEC */
static const int MCTP_I3C_MAXMTU = MCTP_I3C_MAXBUF - 1;
/* 4 byte MCTP header, no data, 1 byte PEC */
static const int MCTP_I3C_MINLEN = 4 + 1;

/* Sufficient for 64kB at min mtu */
static const int MCTP_I3C_TX_QUEUE_LEN = 1100;

/* Somewhat arbitrary */
static const int MCTP_I3C_IBI_SLOTS = 8;

/* Mandatory Data Byte in an IBI, from DSP0233 */
#define I3C_MDB_MCTP 0xAE
/* From MIPI Device Characteristics Register (DCR) Assignments */
#define I3C_DCR_MCTP 0xCC

static const char *MCTP_I3C_OF_PROP = "mctp-controller";

/* List of mctp_i3c_busdev */
static LIST_HEAD(busdevs);
/* Protects busdevs, as well as mctp_i3c_bus.devs lists */
static DEFINE_MUTEX(busdevs_lock);

struct mctp_i3c_bus {
	struct net_device *ndev;

	struct task_struct *tx_thread;
	wait_queue_head_t tx_wq;
	/* tx_lock protects tx_skb and devs */
	spinlock_t tx_lock;
	/* Next skb to transmit */
	struct sk_buff *tx_skb;
	/* Scratch buffer for xmit */
	u8 tx_scratch[MCTP_I3C_MAXBUF];

	/* Element of busdevs */
	struct list_head list;

	/* Provisioned ID of our controller */
	u64 pid;

	struct i3c_bus *bus;
	/* Head of mctp_i3c_device.list. Protected by busdevs_lock */
	struct list_head devs;
};

struct mctp_i3c_device {
	struct i3c_device *i3c;
	struct mctp_i3c_bus *mbus;
	struct list_head list; /* Element of mctp_i3c_bus.devs */

	/* Held while tx_thread is using this device */
	struct mutex lock;

	/* Whether BCR indicates MDB is present in IBI */
	bool have_mdb;
	/* I3C dynamic address */
	u8 addr;
	/* Maximum read length */
	u16 mrl;
	/* Maximum write length */
	u16 mwl;
	/* Provisioned ID */
	u64 pid;
};

/* We synthesise a mac header using the Provisioned ID.
 * Used to pass dest to mctp_i3c_start_xmit.
 */
struct mctp_i3c_internal_hdr {
	u8 dest[PID_SIZE];
	u8 source[PID_SIZE];
} __packed;

static int mctp_i3c_read(struct mctp_i3c_device *mi)
{
	struct i3c_priv_xfer xfer = { .rnw = 1, .len = mi->mrl };
	struct net_device_stats *stats = &mi->mbus->ndev->stats;
	struct mctp_i3c_internal_hdr *ihdr = NULL;
	struct sk_buff *skb = NULL;
	struct mctp_skb_cb *cb;
	int net_status, rc;
	u8 pec, addr;

	skb = netdev_alloc_skb(mi->mbus->ndev,
			       mi->mrl + sizeof(struct mctp_i3c_internal_hdr));
	if (!skb) {
		stats->rx_dropped++;
		rc = -ENOMEM;
		goto err;
	}

	skb->protocol = htons(ETH_P_MCTP);
	/* Create a header for internal use */
	skb_reset_mac_header(skb);
	ihdr = skb_put(skb, sizeof(struct mctp_i3c_internal_hdr));
	put_unaligned_be48(mi->pid, ihdr->source);
	put_unaligned_be48(mi->mbus->pid, ihdr->dest);
	skb_pull(skb, sizeof(struct mctp_i3c_internal_hdr));

	xfer.data.in = skb_put(skb, mi->mrl);

	rc = i3c_device_do_priv_xfers(mi->i3c, &xfer, 1);
	if (rc < 0)
		goto err;

	if (WARN_ON_ONCE(xfer.len > mi->mrl)) {
		/* Bad i3c bus driver */
		rc = -EIO;
		goto err;
	}
	if (xfer.len < MCTP_I3C_MINLEN) {
		stats->rx_length_errors++;
		rc = -EIO;
		goto err;
	}

	/* check PEC, including address byte */
	addr = mi->addr << 1 | 1;
	pec = i2c_smbus_pec(0, &addr, 1);
	pec = i2c_smbus_pec(pec, xfer.data.in, xfer.len - 1);
	if (pec != ((u8 *)xfer.data.in)[xfer.len - 1]) {
		stats->rx_crc_errors++;
		rc = -EINVAL;
		goto err;
	}

	/* Remove PEC */
	skb_trim(skb, xfer.len - 1);

	cb = __mctp_cb(skb);
	cb->halen = PID_SIZE;
	put_unaligned_be48(mi->pid, cb->haddr);

	net_status = netif_rx(skb);

	if (net_status == NET_RX_SUCCESS) {
		stats->rx_packets++;
		stats->rx_bytes += xfer.len - 1;
	} else {
		stats->rx_dropped++;
	}

	return 0;
err:
	kfree_skb(skb);
	return rc;
}

static void mctp_i3c_ibi_handler(struct i3c_device *i3c,
				 const struct i3c_ibi_payload *payload)
{
	struct mctp_i3c_device *mi = i3cdev_get_drvdata(i3c);

	if (WARN_ON_ONCE(!mi))
		return;

	if (mi->have_mdb) {
		if (payload->len > 0) {
			if (((u8 *)payload->data)[0] != I3C_MDB_MCTP) {
				/* Not a mctp-i3c interrupt, ignore it */
				return;
			}
		} else {
			/* The BCR advertised a Mandatory Data Byte but the
			 * device didn't send one.
			 */
			dev_warn_once(i3cdev_to_dev(i3c), "IBI with missing MDB");
		}
	}

	mctp_i3c_read(mi);
}

static int mctp_i3c_setup(struct mctp_i3c_device *mi)
{
	const struct i3c_ibi_setup ibi = {
		.max_payload_len = 1,
		.num_slots = MCTP_I3C_IBI_SLOTS,
		.handler = mctp_i3c_ibi_handler,
	};
	struct i3c_device_info info;
	int rc;

	i3c_device_get_info(mi->i3c, &info);
	mi->have_mdb = info.bcr & BIT(2);
	mi->addr = info.dyn_addr;
	mi->mwl = info.max_write_len;
	mi->mrl = info.max_read_len;
	mi->pid = info.pid;

	rc = i3c_device_request_ibi(mi->i3c, &ibi);
	if (rc == -ENOTSUPP) {
		/* This driver only supports In-Band Interrupt mode.
		 * Support for Polling Mode could be added if required.
		 * (ENOTSUPP is from the i3c layer, not EOPNOTSUPP).
		 */
		dev_warn(i3cdev_to_dev(mi->i3c),
			 "Failed, bus driver doesn't support In-Band Interrupts");
		goto err;
	} else if (rc < 0) {
		dev_err(i3cdev_to_dev(mi->i3c),
			"Failed requesting IBI (%d)\n", rc);
		goto err;
	}

	rc = i3c_device_enable_ibi(mi->i3c);
	if (rc < 0) {
		/* Assume a driver supporting request_ibi also
		 * supports enable_ibi.
		 */
		dev_err(i3cdev_to_dev(mi->i3c), "Failed enabling IBI (%d)\n", rc);
		goto err_free_ibi;
	}

	return 0;

err_free_ibi:
	i3c_device_free_ibi(mi->i3c);

err:
	return rc;
}

/* Adds a new MCTP i3c_device to a bus */
static int mctp_i3c_add_device(struct mctp_i3c_bus *mbus,
			       struct i3c_device *i3c)
__must_hold(&busdevs_lock)
{
	struct mctp_i3c_device *mi = NULL;
	int rc;

	mi = kzalloc(sizeof(*mi), GFP_KERNEL);
	if (!mi) {
		rc = -ENOMEM;
		goto err;
	}
	mi->mbus = mbus;
	mi->i3c = i3c;
	mutex_init(&mi->lock);
	list_add(&mi->list, &mbus->devs);

	i3cdev_set_drvdata(i3c, mi);
	rc = mctp_i3c_setup(mi);
	if (rc < 0)
		goto err_free;

	return 0;

err_free:
	list_del(&mi->list);
	kfree(mi);

err:
	dev_warn(i3cdev_to_dev(i3c), "Error adding mctp-i3c device, %d\n", rc);
	return rc;
}

static int mctp_i3c_probe(struct i3c_device *i3c)
{
	struct mctp_i3c_bus *b = NULL, *mbus = NULL;

	/* Look for a known bus */
	mutex_lock(&busdevs_lock);
	list_for_each_entry(b, &busdevs, list)
		if (b->bus == i3c->bus) {
			mbus = b;
			break;
		}
	mutex_unlock(&busdevs_lock);

	if (!mbus) {
		/* probably no "mctp-controller" property on the i3c bus */
		return -ENODEV;
	}

	return mctp_i3c_add_device(mbus, i3c);
}

static void mctp_i3c_remove_device(struct mctp_i3c_device *mi)
__must_hold(&busdevs_lock)
{
	/* Ensure the tx thread isn't using the device */
	mutex_lock(&mi->lock);

	/* Counterpart of mctp_i3c_setup */
	i3c_device_disable_ibi(mi->i3c);
	i3c_device_free_ibi(mi->i3c);

	/* Counterpart of mctp_i3c_add_device */
	i3cdev_set_drvdata(mi->i3c, NULL);
	list_del(&mi->list);

	/* Safe to unlock after removing from the list */
	mutex_unlock(&mi->lock);
	kfree(mi);
}

static void mctp_i3c_remove(struct i3c_device *i3c)
{
	struct mctp_i3c_device *mi = i3cdev_get_drvdata(i3c);

	/* We my have received a Bus Remove notify prior to device remove,
	 * so mi will already be removed.
	 */
	if (!mi)
		return;

	mutex_lock(&busdevs_lock);
	mctp_i3c_remove_device(mi);
	mutex_unlock(&busdevs_lock);
}

/* Returns the device for an address, with mi->lock held */
static struct mctp_i3c_device *
mctp_i3c_lookup(struct mctp_i3c_bus *mbus, u64 pid)
{
	struct mctp_i3c_device *mi = NULL, *ret = NULL;

	mutex_lock(&busdevs_lock);
	list_for_each_entry(mi, &mbus->devs, list)
		if (mi->pid == pid) {
			ret = mi;
			mutex_lock(&mi->lock);
			break;
		}
	mutex_unlock(&busdevs_lock);
	return ret;
}

static void mctp_i3c_xmit(struct mctp_i3c_bus *mbus, struct sk_buff *skb)
{
	struct net_device_stats *stats = &mbus->ndev->stats;
	struct i3c_priv_xfer xfer = { .rnw = false };
	struct mctp_i3c_internal_hdr *ihdr = NULL;
	struct mctp_i3c_device *mi = NULL;
	unsigned int data_len;
	u8 *data = NULL;
	u8 addr, pec;
	int rc = 0;
	u64 pid;

	skb_pull(skb, sizeof(struct mctp_i3c_internal_hdr));
	data_len = skb->len;

	ihdr = (void *)skb_mac_header(skb);

	pid = get_unaligned_be48(ihdr->dest);
	mi = mctp_i3c_lookup(mbus, pid);
	if (!mi) {
		/* I3C endpoint went away after the packet was enqueued? */
		stats->tx_dropped++;
		goto out;
	}

	if (WARN_ON_ONCE(data_len + 1 > MCTP_I3C_MAXBUF))
		goto out;

	if (data_len + 1 > (unsigned int)mi->mwl) {
		/* Route MTU was larger than supported by the endpoint */
		stats->tx_dropped++;
		goto out;
	}

	/* Need a linear buffer with space for the PEC */
	xfer.len = data_len + 1;
	if (skb_tailroom(skb) >= 1) {
		skb_put(skb, 1);
		data = skb->data;
	} else {
		/* Otherwise need to copy the buffer */
		skb_copy_bits(skb, 0, mbus->tx_scratch, skb->len);
		data = mbus->tx_scratch;
	}

	/* PEC calculation */
	addr = mi->addr << 1;
	pec = i2c_smbus_pec(0, &addr, 1);
	pec = i2c_smbus_pec(pec, data, data_len);
	data[data_len] = pec;

	xfer.data.out = data;
	rc = i3c_device_do_priv_xfers(mi->i3c, &xfer, 1);
	if (rc == 0) {
		stats->tx_bytes += data_len;
		stats->tx_packets++;
	} else {
		stats->tx_errors++;
	}

out:
	if (mi)
		mutex_unlock(&mi->lock);
}

static int mctp_i3c_tx_thread(void *data)
{
	struct mctp_i3c_bus *mbus = data;
	struct sk_buff *skb;

	for (;;) {
		if (kthread_should_stop())
			break;

		spin_lock_bh(&mbus->tx_lock);
		skb = mbus->tx_skb;
		mbus->tx_skb = NULL;
		spin_unlock_bh(&mbus->tx_lock);

		if (netif_queue_stopped(mbus->ndev))
			netif_wake_queue(mbus->ndev);

		if (skb) {
			mctp_i3c_xmit(mbus, skb);
			kfree_skb(skb);
		} else {
			wait_event_idle(mbus->tx_wq,
					mbus->tx_skb || kthread_should_stop());
		}
	}

	return 0;
}

static netdev_tx_t mctp_i3c_start_xmit(struct sk_buff *skb,
				       struct net_device *ndev)
{
	struct mctp_i3c_bus *mbus = netdev_priv(ndev);
	netdev_tx_t ret;

	spin_lock(&mbus->tx_lock);
	netif_stop_queue(ndev);
	if (mbus->tx_skb) {
		dev_warn_ratelimited(&ndev->dev, "TX with queue stopped");
		ret = NETDEV_TX_BUSY;
	} else {
		mbus->tx_skb = skb;
		ret = NETDEV_TX_OK;
	}
	spin_unlock(&mbus->tx_lock);

	if (ret == NETDEV_TX_OK)
		wake_up(&mbus->tx_wq);

	return ret;
}

static void mctp_i3c_bus_free(struct mctp_i3c_bus *mbus)
__must_hold(&busdevs_lock)
{
	struct mctp_i3c_device *mi = NULL, *tmp = NULL;

	if (mbus->tx_thread) {
		kthread_stop(mbus->tx_thread);
		mbus->tx_thread = NULL;
	}

	/* Remove any child devices */
	list_for_each_entry_safe(mi, tmp, &mbus->devs, list) {
		mctp_i3c_remove_device(mi);
	}

	kfree_skb(mbus->tx_skb);
	list_del(&mbus->list);
}

static void mctp_i3c_ndo_uninit(struct net_device *ndev)
{
	struct mctp_i3c_bus *mbus = netdev_priv(ndev);

	/* Perform cleanup here to ensure there are no remaining references */
	mctp_i3c_bus_free(mbus);
}

static int mctp_i3c_header_create(struct sk_buff *skb, struct net_device *dev,
				  unsigned short type, const void *daddr,
	   const void *saddr, unsigned int len)
{
	struct mctp_i3c_internal_hdr *ihdr;

	skb_push(skb, sizeof(struct mctp_i3c_internal_hdr));
	skb_reset_mac_header(skb);
	ihdr = (void *)skb_mac_header(skb);
	memcpy(ihdr->dest, daddr, PID_SIZE);
	memcpy(ihdr->source, saddr, PID_SIZE);
	return 0;
}

static const struct net_device_ops mctp_i3c_ops = {
	.ndo_start_xmit = mctp_i3c_start_xmit,
	.ndo_uninit = mctp_i3c_ndo_uninit,
};

static const struct header_ops mctp_i3c_headops = {
	.create = mctp_i3c_header_create,
};

static void mctp_i3c_net_setup(struct net_device *dev)
{
	dev->type = ARPHRD_MCTP;

	dev->mtu = MCTP_I3C_MAXMTU;
	dev->min_mtu = MCTP_I3C_MINMTU;
	dev->max_mtu = MCTP_I3C_MAXMTU;
	dev->tx_queue_len = MCTP_I3C_TX_QUEUE_LEN;

	dev->hard_header_len = sizeof(struct mctp_i3c_internal_hdr);
	dev->addr_len = PID_SIZE;

	dev->netdev_ops	= &mctp_i3c_ops;
	dev->header_ops	= &mctp_i3c_headops;
}

static bool mctp_i3c_is_mctp_controller(struct i3c_bus *bus)
{
	struct i3c_dev_desc *master = bus->cur_master;

	if (!master)
		return false;

	return of_property_read_bool(master->common.master->dev.of_node,
				     MCTP_I3C_OF_PROP);
}

/* Returns the Provisioned Id of a local bus master */
static int mctp_i3c_bus_local_pid(struct i3c_bus *bus, u64 *ret_pid)
{
	struct i3c_dev_desc *master;

	master = bus->cur_master;
	if (WARN_ON_ONCE(!master))
		return -ENOENT;
	*ret_pid = master->info.pid;

	return 0;
}

/* Returns an ERR_PTR on failure */
static struct mctp_i3c_bus *mctp_i3c_bus_add(struct i3c_bus *bus)
__must_hold(&busdevs_lock)
{
	struct mctp_i3c_bus *mbus = NULL;
	struct net_device *ndev = NULL;
	char namebuf[IFNAMSIZ];
	u8 addr[PID_SIZE];
	int rc;

	if (!mctp_i3c_is_mctp_controller(bus))
		return ERR_PTR(-ENOENT);

	snprintf(namebuf, sizeof(namebuf), "mctpi3c%d", bus->id);
	ndev = alloc_netdev(sizeof(*mbus), namebuf, NET_NAME_ENUM,
			    mctp_i3c_net_setup);
	if (!ndev) {
		rc = -ENOMEM;
		goto err;
	}

	mbus = netdev_priv(ndev);
	mbus->ndev = ndev;
	mbus->bus = bus;
	INIT_LIST_HEAD(&mbus->devs);
	list_add(&mbus->list, &busdevs);

	rc = mctp_i3c_bus_local_pid(bus, &mbus->pid);
	if (rc < 0) {
		dev_err(&ndev->dev, "No I3C PID available\n");
		goto err_free_uninit;
	}
	put_unaligned_be48(mbus->pid, addr);
	dev_addr_set(ndev, addr);

	init_waitqueue_head(&mbus->tx_wq);
	spin_lock_init(&mbus->tx_lock);
	mbus->tx_thread = kthread_run(mctp_i3c_tx_thread, mbus,
				      "%s/tx", ndev->name);
	if (IS_ERR(mbus->tx_thread)) {
		dev_warn(&ndev->dev, "Error creating thread: %pe\n",
			 mbus->tx_thread);
		rc = PTR_ERR(mbus->tx_thread);
		mbus->tx_thread = NULL;
		goto err_free_uninit;
	}

	rc = mctp_register_netdev(ndev, NULL);
	if (rc < 0) {
		dev_warn(&ndev->dev, "netdev register failed: %d\n", rc);
		goto err_free_netdev;
	}
	return mbus;

err_free_uninit:
	/* uninit will not get called if a netdev has not been registered,
	 * so we perform the same mbus cleanup manually.
	 */
	mctp_i3c_bus_free(mbus);

err_free_netdev:
	free_netdev(ndev);

err:
	return ERR_PTR(rc);
}

static void mctp_i3c_bus_remove(struct mctp_i3c_bus *mbus)
__must_hold(&busdevs_lock)
{
	/* Unregister calls through to ndo_uninit -> mctp_i3c_bus_free() */
	mctp_unregister_netdev(mbus->ndev);

	free_netdev(mbus->ndev);
	/* mbus is deallocated */
}

/* Removes all mctp-i3c busses */
static void mctp_i3c_bus_remove_all(void)
{
	struct mctp_i3c_bus *mbus = NULL, *tmp = NULL;

	mutex_lock(&busdevs_lock);
	list_for_each_entry_safe(mbus, tmp, &busdevs, list) {
		mctp_i3c_bus_remove(mbus);
	}
	mutex_unlock(&busdevs_lock);
}

/* Adds a i3c_bus if it isn't already in the busdevs list.
 * Suitable as an i3c_for_each_bus_locked callback.
 */
static int mctp_i3c_bus_add_new(struct i3c_bus *bus, void *data)
{
	struct mctp_i3c_bus *mbus = NULL, *tmp = NULL;
	bool exists = false;

	mutex_lock(&busdevs_lock);
	list_for_each_entry_safe(mbus, tmp, &busdevs, list)
		if (mbus->bus == bus)
			exists = true;

	/* It is OK for a bus to already exist. That can occur due to
	 * the race in mod_init between notifier and for_each_bus
	 */
	if (!exists)
		mctp_i3c_bus_add(bus);
	mutex_unlock(&busdevs_lock);
	return 0;
}

static void mctp_i3c_notify_bus_remove(struct i3c_bus *bus)
{
	struct mctp_i3c_bus *mbus = NULL, *tmp;

	mutex_lock(&busdevs_lock);
	list_for_each_entry_safe(mbus, tmp, &busdevs, list)
		if (mbus->bus == bus)
			mctp_i3c_bus_remove(mbus);
	mutex_unlock(&busdevs_lock);
}

static int mctp_i3c_notifier_call(struct notifier_block *nb,
				  unsigned long action, void *data)
{
	switch (action) {
	case I3C_NOTIFY_BUS_ADD:
		mctp_i3c_bus_add_new((struct i3c_bus *)data, NULL);
		break;
	case I3C_NOTIFY_BUS_REMOVE:
		mctp_i3c_notify_bus_remove((struct i3c_bus *)data);
		break;
	}
	return NOTIFY_DONE;
}

static struct notifier_block mctp_i3c_notifier = {
	.notifier_call = mctp_i3c_notifier_call,
};

static const struct i3c_device_id mctp_i3c_ids[] = {
	I3C_CLASS(I3C_DCR_MCTP, NULL),
	{ 0 },
};

static struct i3c_driver mctp_i3c_driver = {
	.driver = {
		.name = "mctp-i3c",
	},
	.probe = mctp_i3c_probe,
	.remove = mctp_i3c_remove,
	.id_table = mctp_i3c_ids,
};

static __init int mctp_i3c_mod_init(void)
{
	int rc;

	rc = i3c_register_notifier(&mctp_i3c_notifier);
	if (rc < 0) {
		i3c_driver_unregister(&mctp_i3c_driver);
		return rc;
	}

	i3c_for_each_bus_locked(mctp_i3c_bus_add_new, NULL);

	rc = i3c_driver_register(&mctp_i3c_driver);
	if (rc < 0)
		return rc;

	return 0;
}

static __exit void mctp_i3c_mod_exit(void)
{
	int rc;

	i3c_driver_unregister(&mctp_i3c_driver);

	rc = i3c_unregister_notifier(&mctp_i3c_notifier);
	if (rc < 0)
		pr_warn("MCTP I3C could not unregister notifier, %d\n", rc);

	mctp_i3c_bus_remove_all();
}

module_init(mctp_i3c_mod_init);
module_exit(mctp_i3c_mod_exit);

MODULE_DEVICE_TABLE(i3c, mctp_i3c_ids);
MODULE_DESCRIPTION("MCTP I3C device");
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Matt Johnston <matt@codeconstruct.com.au>");