Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

4 files changed, 1661 insertions, 0 deletions

diff --git a/drivers/net/mctp/Kconfig b/drivers/net/mctp/Kconfig
new file mode 100644
index 000000000..dc71657d9
--- /dev/null
+++ b/drivers/net/mctp/Kconfig
@@ -0,0 +1,38 @@
+
+if MCTP
+
+menu "MCTP Device Drivers"
+
+config MCTP_SERIAL
+	tristate "MCTP serial transport"
+	depends on TTY
+	select CRC_CCITT
+	help
+	  This driver provides an MCTP-over-serial interface, through a
+	  serial line-discipline, as defined by DMTF specification "DSP0253 -
+	  MCTP Serial Transport Binding". By attaching the ldisc to a serial
+	  device, we get a new net device to transport MCTP packets.
+
+	  This allows communication with external MCTP endpoints which use
+	  serial as their transport. It can also be used as an easy way to
+	  provide MCTP connectivity between virtual machines, by forwarding
+	  data between simple virtual serial devices.
+
+	  Say y here if you need to connect to MCTP endpoints over serial. To
+	  compile as a module, use m; the module will be called mctp-serial.
+
+config MCTP_TRANSPORT_I2C
+	tristate "MCTP SMBus/I2C transport"
+	# i2c-mux is optional, but we must build as a module if i2c-mux is a module
+	depends on I2C_MUX || !I2C_MUX
+	depends on I2C
+	depends on I2C_SLAVE
+	select MCTP_FLOWS
+	help
+	  Provides a driver to access MCTP devices over SMBus/I2C transport,
+	  from DMTF specification DSP0237. A MCTP protocol network device is
+	  created for each I2C bus that has been assigned a mctp-i2c device.
+
+endmenu
+
+endif
diff --git a/drivers/net/mctp/Makefile b/drivers/net/mctp/Makefile
new file mode 100644
index 000000000..1ca3e6028
--- /dev/null
+++ b/drivers/net/mctp/Makefile
@@ -0,0 +1,2 @@
+obj-$(CONFIG_MCTP_SERIAL) += mctp-serial.o
+obj-$(CONFIG_MCTP_TRANSPORT_I2C) += mctp-i2c.o
diff --git a/drivers/net/mctp/mctp-i2c.c b/drivers/net/mctp/mctp-i2c.c
new file mode 100644
index 000000000..1d67a3ca1
--- /dev/null
+++ b/drivers/net/mctp/mctp-i2c.c
@@ -0,0 +1,1097 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Management Controller Transport Protocol (MCTP)
+ * Implements DMTF specification
+ * "DSP0237 Management Component Transport Protocol (MCTP) SMBus/I2C
+ * Transport Binding"
+ * https://www.dmtf.org/sites/default/files/standards/documents/DSP0237_1.2.0.pdf
+ *
+ * A netdev is created for each I2C bus that handles MCTP. In the case of an I2C
+ * mux topology a single I2C client is attached to the root of the mux topology,
+ * shared between all mux I2C busses underneath. For non-mux cases an I2C client
+ * is attached per netdev.
+ *
+ * mctp-i2c-controller.yml devicetree binding has further details.
+ *
+ * Copyright (c) 2022 Code Construct
+ * Copyright (c) 2022 Google
+ */
+
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/i2c.h>
+#include <linux/i2c-mux.h>
+#include <linux/if_arp.h>
+#include <net/mctp.h>
+#include <net/mctpdevice.h>
+
+/* byte_count is limited to u8 */
+#define MCTP_I2C_MAXBLOCK 255
+/* One byte is taken by source_slave */
+#define MCTP_I2C_MAXMTU (MCTP_I2C_MAXBLOCK - 1)
+#define MCTP_I2C_MINMTU (64 + 4)
+/* Allow space for dest_address, command, byte_count, data, PEC */
+#define MCTP_I2C_BUFSZ (3 + MCTP_I2C_MAXBLOCK + 1)
+#define MCTP_I2C_MINLEN 8
+#define MCTP_I2C_COMMANDCODE 0x0f
+#define MCTP_I2C_TX_WORK_LEN 100
+/* Sufficient for 64kB at min mtu */
+#define MCTP_I2C_TX_QUEUE_LEN 1100
+
+#define MCTP_I2C_OF_PROP "mctp-controller"
+
+enum {
+	MCTP_I2C_FLOW_STATE_NEW = 0,
+	MCTP_I2C_FLOW_STATE_ACTIVE,
+	MCTP_I2C_FLOW_STATE_INVALID,
+};
+
+/* List of all struct mctp_i2c_client
+ * Lock protects driver_clients and also prevents adding/removing adapters
+ * during mctp_i2c_client probe/remove.
+ */
+static DEFINE_MUTEX(driver_clients_lock);
+static LIST_HEAD(driver_clients);
+
+struct mctp_i2c_client;
+
+/* The netdev structure. One of these per I2C adapter. */
+struct mctp_i2c_dev {
+	struct net_device *ndev;
+	struct i2c_adapter *adapter;
+	struct mctp_i2c_client *client;
+	struct list_head list; /* For mctp_i2c_client.devs */
+
+	size_t rx_pos;
+	u8 rx_buffer[MCTP_I2C_BUFSZ];
+	struct completion rx_done;
+
+	struct task_struct *tx_thread;
+	wait_queue_head_t tx_wq;
+	struct sk_buff_head tx_queue;
+	u8 tx_scratch[MCTP_I2C_BUFSZ];
+
+	/* A fake entry in our tx queue to perform an unlock operation */
+	struct sk_buff unlock_marker;
+
+	/* Spinlock protects i2c_lock_count, release_count, allow_rx */
+	spinlock_t lock;
+	int i2c_lock_count;
+	int release_count;
+	/* Indicates that the netif is ready to receive incoming packets */
+	bool allow_rx;
+
+};
+
+/* The i2c client structure. One per hardware i2c bus at the top of the
+ * mux tree, shared by multiple netdevs
+ */
+struct mctp_i2c_client {
+	struct i2c_client *client;
+	u8 lladdr;
+
+	struct mctp_i2c_dev *sel;
+	struct list_head devs;
+	spinlock_t sel_lock; /* Protects sel and devs */
+
+	struct list_head list; /* For driver_clients */
+};
+
+/* Header on the wire. */
+struct mctp_i2c_hdr {
+	u8 dest_slave;
+	u8 command;
+	/* Count of bytes following byte_count, excluding PEC */
+	u8 byte_count;
+	u8 source_slave;
+};
+
+static int mctp_i2c_recv(struct mctp_i2c_dev *midev);
+static int mctp_i2c_slave_cb(struct i2c_client *client,
+			     enum i2c_slave_event event, u8 *val);
+static void mctp_i2c_ndo_uninit(struct net_device *dev);
+static int mctp_i2c_ndo_open(struct net_device *dev);
+
+static struct i2c_adapter *mux_root_adapter(struct i2c_adapter *adap)
+{
+#if IS_ENABLED(CONFIG_I2C_MUX)
+	return i2c_root_adapter(&adap->dev);
+#else
+	/* In non-mux config all i2c adapters are root adapters */
+	return adap;
+#endif
+}
+
+/* Creates a new i2c slave device attached to the root adapter.
+ * Sets up the slave callback.
+ * Must be called with a client on a root adapter.
+ */
+static struct mctp_i2c_client *mctp_i2c_new_client(struct i2c_client *client)
+{
+	struct mctp_i2c_client *mcli = NULL;
+	struct i2c_adapter *root = NULL;
+	int rc;
+
+	if (client->flags & I2C_CLIENT_TEN) {
+		dev_err(&client->dev, "failed, MCTP requires a 7-bit I2C address, addr=0x%x\n",
+			client->addr);
+		rc = -EINVAL;
+		goto err;
+	}
+
+	root = mux_root_adapter(client->adapter);
+	if (!root) {
+		dev_err(&client->dev, "failed to find root adapter\n");
+		rc = -ENOENT;
+		goto err;
+	}
+	if (root != client->adapter) {
+		dev_err(&client->dev,
+			"A mctp-i2c-controller client cannot be placed on an I2C mux adapter.\n"
+			" It should be placed on the mux tree root adapter\n"
+			" then set mctp-controller property on adapters to attach\n");
+		rc = -EINVAL;
+		goto err;
+	}
+
+	mcli = kzalloc(sizeof(*mcli), GFP_KERNEL);
+	if (!mcli) {
+		rc = -ENOMEM;
+		goto err;
+	}
+	spin_lock_init(&mcli->sel_lock);
+	INIT_LIST_HEAD(&mcli->devs);
+	INIT_LIST_HEAD(&mcli->list);
+	mcli->lladdr = client->addr & 0xff;
+	mcli->client = client;
+	i2c_set_clientdata(client, mcli);
+
+	rc = i2c_slave_register(mcli->client, mctp_i2c_slave_cb);
+	if (rc < 0) {
+		dev_err(&client->dev, "i2c register failed %d\n", rc);
+		mcli->client = NULL;
+		i2c_set_clientdata(client, NULL);
+		goto err;
+	}
+
+	return mcli;
+err:
+	if (mcli) {
+		if (mcli->client)
+			i2c_unregister_device(mcli->client);
+		kfree(mcli);
+	}
+	return ERR_PTR(rc);
+}
+
+static void mctp_i2c_free_client(struct mctp_i2c_client *mcli)
+{
+	int rc;
+
+	WARN_ON(!mutex_is_locked(&driver_clients_lock));
+	WARN_ON(!list_empty(&mcli->devs));
+	WARN_ON(mcli->sel); /* sanity check, no locking */
+
+	rc = i2c_slave_unregister(mcli->client);
+	/* Leak if it fails, we can't propagate errors upwards */
+	if (rc < 0)
+		dev_err(&mcli->client->dev, "i2c unregister failed %d\n", rc);
+	else
+		kfree(mcli);
+}
+
+/* Switch the mctp i2c device to receive responses.
+ * Call with sel_lock held
+ */
+static void __mctp_i2c_device_select(struct mctp_i2c_client *mcli,
+				     struct mctp_i2c_dev *midev)
+{
+	assert_spin_locked(&mcli->sel_lock);
+	if (midev)
+		dev_hold(midev->ndev);
+	if (mcli->sel)
+		dev_put(mcli->sel->ndev);
+	mcli->sel = midev;
+}
+
+/* Switch the mctp i2c device to receive responses */
+static void mctp_i2c_device_select(struct mctp_i2c_client *mcli,
+				   struct mctp_i2c_dev *midev)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&mcli->sel_lock, flags);
+	__mctp_i2c_device_select(mcli, midev);
+	spin_unlock_irqrestore(&mcli->sel_lock, flags);
+}
+
+static int mctp_i2c_slave_cb(struct i2c_client *client,
+			     enum i2c_slave_event event, u8 *val)
+{
+	struct mctp_i2c_client *mcli = i2c_get_clientdata(client);
+	struct mctp_i2c_dev *midev = NULL;
+	unsigned long flags;
+	int rc = 0;
+
+	spin_lock_irqsave(&mcli->sel_lock, flags);
+	midev = mcli->sel;
+	if (midev)
+		dev_hold(midev->ndev);
+	spin_unlock_irqrestore(&mcli->sel_lock, flags);
+
+	if (!midev)
+		return 0;
+
+	switch (event) {
+	case I2C_SLAVE_WRITE_RECEIVED:
+		if (midev->rx_pos < MCTP_I2C_BUFSZ) {
+			midev->rx_buffer[midev->rx_pos] = *val;
+			midev->rx_pos++;
+		} else {
+			midev->ndev->stats.rx_over_errors++;
+		}
+
+		break;
+	case I2C_SLAVE_WRITE_REQUESTED:
+		/* dest_slave as first byte */
+		midev->rx_buffer[0] = mcli->lladdr << 1;
+		midev->rx_pos = 1;
+		break;
+	case I2C_SLAVE_STOP:
+		rc = mctp_i2c_recv(midev);
+		break;
+	default:
+		break;
+	}
+
+	dev_put(midev->ndev);
+	return rc;
+}
+
+/* Processes incoming data that has been accumulated by the slave cb */
+static int mctp_i2c_recv(struct mctp_i2c_dev *midev)
+{
+	struct net_device *ndev = midev->ndev;
+	struct mctp_i2c_hdr *hdr;
+	struct mctp_skb_cb *cb;
+	struct sk_buff *skb;
+	unsigned long flags;
+	u8 pec, calc_pec;
+	size_t recvlen;
+	int status;
+
+	/* + 1 for the PEC */
+	if (midev->rx_pos < MCTP_I2C_MINLEN + 1) {
+		ndev->stats.rx_length_errors++;
+		return -EINVAL;
+	}
+	/* recvlen excludes PEC */
+	recvlen = midev->rx_pos - 1;
+
+	hdr = (void *)midev->rx_buffer;
+	if (hdr->command != MCTP_I2C_COMMANDCODE) {
+		ndev->stats.rx_dropped++;
+		return -EINVAL;
+	}
+
+	if (hdr->byte_count + offsetof(struct mctp_i2c_hdr, source_slave) != recvlen) {
+		ndev->stats.rx_length_errors++;
+		return -EINVAL;
+	}
+
+	pec = midev->rx_buffer[midev->rx_pos - 1];
+	calc_pec = i2c_smbus_pec(0, midev->rx_buffer, recvlen);
+	if (pec != calc_pec) {
+		ndev->stats.rx_crc_errors++;
+		return -EINVAL;
+	}
+
+	skb = netdev_alloc_skb(ndev, recvlen);
+	if (!skb) {
+		ndev->stats.rx_dropped++;
+		return -ENOMEM;
+	}
+
+	skb->protocol = htons(ETH_P_MCTP);
+	skb_put_data(skb, midev->rx_buffer, recvlen);
+	skb_reset_mac_header(skb);
+	skb_pull(skb, sizeof(struct mctp_i2c_hdr));
+	skb_reset_network_header(skb);
+
+	cb = __mctp_cb(skb);
+	cb->halen = 1;
+	cb->haddr[0] = hdr->source_slave >> 1;
+
+	/* We need to ensure that the netif is not used once netdev
+	 * unregister occurs
+	 */
+	spin_lock_irqsave(&midev->lock, flags);
+	if (midev->allow_rx) {
+		reinit_completion(&midev->rx_done);
+		spin_unlock_irqrestore(&midev->lock, flags);
+
+		status = netif_rx(skb);
+		complete(&midev->rx_done);
+	} else {
+		status = NET_RX_DROP;
+		spin_unlock_irqrestore(&midev->lock, flags);
+	}
+
+	if (status == NET_RX_SUCCESS) {
+		ndev->stats.rx_packets++;
+		ndev->stats.rx_bytes += recvlen;
+	} else {
+		ndev->stats.rx_dropped++;
+	}
+	return 0;
+}
+
+enum mctp_i2c_flow_state {
+	MCTP_I2C_TX_FLOW_INVALID,
+	MCTP_I2C_TX_FLOW_NONE,
+	MCTP_I2C_TX_FLOW_NEW,
+	MCTP_I2C_TX_FLOW_EXISTING,
+};
+
+static enum mctp_i2c_flow_state
+mctp_i2c_get_tx_flow_state(struct mctp_i2c_dev *midev, struct sk_buff *skb)
+{
+	enum mctp_i2c_flow_state state;
+	struct mctp_sk_key *key;
+	struct mctp_flow *flow;
+	unsigned long flags;
+
+	flow = skb_ext_find(skb, SKB_EXT_MCTP);
+	if (!flow)
+		return MCTP_I2C_TX_FLOW_NONE;
+
+	key = flow->key;
+	if (!key)
+		return MCTP_I2C_TX_FLOW_NONE;
+
+	spin_lock_irqsave(&key->lock, flags);
+	/* If the key is present but invalid, we're unlikely to be able
+	 * to handle the flow at all; just drop now
+	 */
+	if (!key->valid) {
+		state = MCTP_I2C_TX_FLOW_INVALID;
+	} else {
+		switch (key->dev_flow_state) {
+		case MCTP_I2C_FLOW_STATE_NEW:
+			key->dev_flow_state = MCTP_I2C_FLOW_STATE_ACTIVE;
+			state = MCTP_I2C_TX_FLOW_NEW;
+			break;
+		case MCTP_I2C_FLOW_STATE_ACTIVE:
+			state = MCTP_I2C_TX_FLOW_EXISTING;
+			break;
+		default:
+			state = MCTP_I2C_TX_FLOW_INVALID;
+		}
+	}
+
+	spin_unlock_irqrestore(&key->lock, flags);
+
+	return state;
+}
+
+/* We're not contending with ourselves here; we only need to exclude other
+ * i2c clients from using the bus. refcounts are simply to prevent
+ * recursive locking.
+ */
+static void mctp_i2c_lock_nest(struct mctp_i2c_dev *midev)
+{
+	unsigned long flags;
+	bool lock;
+
+	spin_lock_irqsave(&midev->lock, flags);
+	lock = midev->i2c_lock_count == 0;
+	midev->i2c_lock_count++;
+	spin_unlock_irqrestore(&midev->lock, flags);
+
+	if (lock)
+		i2c_lock_bus(midev->adapter, I2C_LOCK_SEGMENT);
+}
+
+static void mctp_i2c_unlock_nest(struct mctp_i2c_dev *midev)
+{
+	unsigned long flags;
+	bool unlock;
+
+	spin_lock_irqsave(&midev->lock, flags);
+	if (!WARN_ONCE(midev->i2c_lock_count == 0, "lock count underflow!"))
+		midev->i2c_lock_count--;
+	unlock = midev->i2c_lock_count == 0;
+	spin_unlock_irqrestore(&midev->lock, flags);
+
+	if (unlock)
+		i2c_unlock_bus(midev->adapter, I2C_LOCK_SEGMENT);
+}
+
+/* Unlocks the bus if was previously locked, used for cleanup */
+static void mctp_i2c_unlock_reset(struct mctp_i2c_dev *midev)
+{
+	unsigned long flags;
+	bool unlock;
+
+	spin_lock_irqsave(&midev->lock, flags);
+	unlock = midev->i2c_lock_count > 0;
+	midev->i2c_lock_count = 0;
+	spin_unlock_irqrestore(&midev->lock, flags);
+
+	if (unlock)
+		i2c_unlock_bus(midev->adapter, I2C_LOCK_SEGMENT);
+}
+
+static void mctp_i2c_xmit(struct mctp_i2c_dev *midev, struct sk_buff *skb)
+{
+	struct net_device_stats *stats = &midev->ndev->stats;
+	enum mctp_i2c_flow_state fs;
+	struct mctp_i2c_hdr *hdr;
+	struct i2c_msg msg = {0};
+	u8 *pecp;
+	int rc;
+
+	fs = mctp_i2c_get_tx_flow_state(midev, skb);
+
+	hdr = (void *)skb_mac_header(skb);
+	/* Sanity check that packet contents matches skb length,
+	 * and can't exceed MCTP_I2C_BUFSZ
+	 */
+	if (skb->len != hdr->byte_count + 3) {
+		dev_warn_ratelimited(&midev->adapter->dev,
+				     "Bad tx length %d vs skb %u\n",
+				     hdr->byte_count + 3, skb->len);
+		return;
+	}
+
+	if (skb_tailroom(skb) >= 1) {
+		/* Linear case with space, we can just append the PEC */
+		skb_put(skb, 1);
+	} else {
+		/* Otherwise need to copy the buffer */
+		skb_copy_bits(skb, 0, midev->tx_scratch, skb->len);
+		hdr = (void *)midev->tx_scratch;
+	}
+
+	pecp = (void *)&hdr->source_slave + hdr->byte_count;
+	*pecp = i2c_smbus_pec(0, (u8 *)hdr, hdr->byte_count + 3);
+	msg.buf = (void *)&hdr->command;
+	/* command, bytecount, data, pec */
+	msg.len = 2 + hdr->byte_count + 1;
+	msg.addr = hdr->dest_slave >> 1;
+
+	switch (fs) {
+	case MCTP_I2C_TX_FLOW_NONE:
+		/* no flow: full lock & unlock */
+		mctp_i2c_lock_nest(midev);
+		mctp_i2c_device_select(midev->client, midev);
+		rc = __i2c_transfer(midev->adapter, &msg, 1);
+		mctp_i2c_unlock_nest(midev);
+		break;
+
+	case MCTP_I2C_TX_FLOW_NEW:
+		/* new flow: lock, tx, but don't unlock; that will happen
+		 * on flow release
+		 */
+		mctp_i2c_lock_nest(midev);
+		mctp_i2c_device_select(midev->client, midev);
+		fallthrough;
+
+	case MCTP_I2C_TX_FLOW_EXISTING:
+		/* existing flow: we already have the lock; just tx */
+		rc = __i2c_transfer(midev->adapter, &msg, 1);
+		break;
+
+	case MCTP_I2C_TX_FLOW_INVALID:
+		return;
+	}
+
+	if (rc < 0) {
+		dev_warn_ratelimited(&midev->adapter->dev,
+				     "__i2c_transfer failed %d\n", rc);
+		stats->tx_errors++;
+	} else {
+		stats->tx_bytes += skb->len;
+		stats->tx_packets++;
+	}
+}
+
+static void mctp_i2c_flow_release(struct mctp_i2c_dev *midev)
+{
+	unsigned long flags;
+	bool unlock;
+
+	spin_lock_irqsave(&midev->lock, flags);
+	if (midev->release_count > midev->i2c_lock_count) {
+		WARN_ONCE(1, "release count overflow");
+		midev->release_count = midev->i2c_lock_count;
+	}
+
+	midev->i2c_lock_count -= midev->release_count;
+	unlock = midev->i2c_lock_count == 0 && midev->release_count > 0;
+	midev->release_count = 0;
+	spin_unlock_irqrestore(&midev->lock, flags);
+
+	if (unlock)
+		i2c_unlock_bus(midev->adapter, I2C_LOCK_SEGMENT);
+}
+
+static int mctp_i2c_header_create(struct sk_buff *skb, struct net_device *dev,
+				  unsigned short type, const void *daddr,
+	   const void *saddr, unsigned int len)
+{
+	struct mctp_i2c_hdr *hdr;
+	struct mctp_hdr *mhdr;
+	u8 lldst, llsrc;
+
+	if (len > MCTP_I2C_MAXMTU)
+		return -EMSGSIZE;
+
+	lldst = *((u8 *)daddr);
+	llsrc = *((u8 *)saddr);
+
+	skb_push(skb, sizeof(struct mctp_i2c_hdr));
+	skb_reset_mac_header(skb);
+	hdr = (void *)skb_mac_header(skb);
+	mhdr = mctp_hdr(skb);
+	hdr->dest_slave = (lldst << 1) & 0xff;
+	hdr->command = MCTP_I2C_COMMANDCODE;
+	hdr->byte_count = len + 1;
+	hdr->source_slave = ((llsrc << 1) & 0xff) | 0x01;
+	mhdr->ver = 0x01;
+
+	return sizeof(struct mctp_i2c_hdr);
+}
+
+static int mctp_i2c_tx_thread(void *data)
+{
+	struct mctp_i2c_dev *midev = data;
+	struct sk_buff *skb;
+	unsigned long flags;
+
+	for (;;) {
+		if (kthread_should_stop())
+			break;
+
+		spin_lock_irqsave(&midev->tx_queue.lock, flags);
+		skb = __skb_dequeue(&midev->tx_queue);
+		if (netif_queue_stopped(midev->ndev))
+			netif_wake_queue(midev->ndev);
+		spin_unlock_irqrestore(&midev->tx_queue.lock, flags);
+
+		if (skb == &midev->unlock_marker) {
+			mctp_i2c_flow_release(midev);
+
+		} else if (skb) {
+			mctp_i2c_xmit(midev, skb);
+			kfree_skb(skb);
+
+		} else {
+			wait_event_idle(midev->tx_wq,
+					!skb_queue_empty(&midev->tx_queue) ||
+				   kthread_should_stop());
+		}
+	}
+
+	return 0;
+}
+
+static netdev_tx_t mctp_i2c_start_xmit(struct sk_buff *skb,
+				       struct net_device *dev)
+{
+	struct mctp_i2c_dev *midev = netdev_priv(dev);
+	unsigned long flags;
+
+	spin_lock_irqsave(&midev->tx_queue.lock, flags);
+	if (skb_queue_len(&midev->tx_queue) >= MCTP_I2C_TX_WORK_LEN) {
+		netif_stop_queue(dev);
+		spin_unlock_irqrestore(&midev->tx_queue.lock, flags);
+		netdev_err(dev, "BUG! Tx Ring full when queue awake!\n");
+		return NETDEV_TX_BUSY;
+	}
+
+	__skb_queue_tail(&midev->tx_queue, skb);
+	if (skb_queue_len(&midev->tx_queue) == MCTP_I2C_TX_WORK_LEN)
+		netif_stop_queue(dev);
+	spin_unlock_irqrestore(&midev->tx_queue.lock, flags);
+
+	wake_up(&midev->tx_wq);
+	return NETDEV_TX_OK;
+}
+
+static void mctp_i2c_release_flow(struct mctp_dev *mdev,
+				  struct mctp_sk_key *key)
+
+{
+	struct mctp_i2c_dev *midev = netdev_priv(mdev->dev);
+	bool queue_release = false;
+	unsigned long flags;
+
+	spin_lock_irqsave(&midev->lock, flags);
+	/* if we have seen the flow/key previously, we need to pair the
+	 * original lock with a release
+	 */
+	if (key->dev_flow_state == MCTP_I2C_FLOW_STATE_ACTIVE) {
+		midev->release_count++;
+		queue_release = true;
+	}
+	key->dev_flow_state = MCTP_I2C_FLOW_STATE_INVALID;
+	spin_unlock_irqrestore(&midev->lock, flags);
+
+	if (queue_release) {
+		/* Ensure we have a release operation queued, through the fake
+		 * marker skb
+		 */
+		spin_lock(&midev->tx_queue.lock);
+		if (!midev->unlock_marker.next)
+			__skb_queue_tail(&midev->tx_queue,
+					 &midev->unlock_marker);
+		spin_unlock(&midev->tx_queue.lock);
+		wake_up(&midev->tx_wq);
+	}
+}
+
+static const struct net_device_ops mctp_i2c_ops = {
+	.ndo_start_xmit = mctp_i2c_start_xmit,
+	.ndo_uninit = mctp_i2c_ndo_uninit,
+	.ndo_open = mctp_i2c_ndo_open,
+};
+
+static const struct header_ops mctp_i2c_headops = {
+	.create = mctp_i2c_header_create,
+};
+
+static const struct mctp_netdev_ops mctp_i2c_mctp_ops = {
+	.release_flow = mctp_i2c_release_flow,
+};
+
+static void mctp_i2c_net_setup(struct net_device *dev)
+{
+	dev->type = ARPHRD_MCTP;
+
+	dev->mtu = MCTP_I2C_MAXMTU;
+	dev->min_mtu = MCTP_I2C_MINMTU;
+	dev->max_mtu = MCTP_I2C_MAXMTU;
+	dev->tx_queue_len = MCTP_I2C_TX_QUEUE_LEN;
+
+	dev->hard_header_len = sizeof(struct mctp_i2c_hdr);
+	dev->addr_len = 1;
+
+	dev->netdev_ops		= &mctp_i2c_ops;
+	dev->header_ops		= &mctp_i2c_headops;
+}
+
+/* Populates the mctp_i2c_dev priv struct for a netdev.
+ * Returns an error pointer on failure.
+ */
+static struct mctp_i2c_dev *mctp_i2c_midev_init(struct net_device *dev,
+						struct mctp_i2c_client *mcli,
+						struct i2c_adapter *adap)
+{
+	struct mctp_i2c_dev *midev = netdev_priv(dev);
+	unsigned long flags;
+
+	midev->tx_thread = kthread_create(mctp_i2c_tx_thread, midev,
+					  "%s/tx", dev->name);
+	if (IS_ERR(midev->tx_thread))
+		return ERR_CAST(midev->tx_thread);
+
+	midev->ndev = dev;
+	get_device(&adap->dev);
+	midev->adapter = adap;
+	get_device(&mcli->client->dev);
+	midev->client = mcli;
+	INIT_LIST_HEAD(&midev->list);
+	spin_lock_init(&midev->lock);
+	midev->i2c_lock_count = 0;
+	midev->release_count = 0;
+	init_completion(&midev->rx_done);
+	complete(&midev->rx_done);
+	init_waitqueue_head(&midev->tx_wq);
+	skb_queue_head_init(&midev->tx_queue);
+
+	/* Add to the parent mcli */
+	spin_lock_irqsave(&mcli->sel_lock, flags);
+	list_add(&midev->list, &mcli->devs);
+	/* Select a device by default */
+	if (!mcli->sel)
+		__mctp_i2c_device_select(mcli, midev);
+	spin_unlock_irqrestore(&mcli->sel_lock, flags);
+
+	/* Start the worker thread */
+	wake_up_process(midev->tx_thread);
+
+	return midev;
+}
+
+/* Counterpart of mctp_i2c_midev_init */
+static void mctp_i2c_midev_free(struct mctp_i2c_dev *midev)
+{
+	struct mctp_i2c_client *mcli = midev->client;
+	unsigned long flags;
+
+	if (midev->tx_thread) {
+		kthread_stop(midev->tx_thread);
+		midev->tx_thread = NULL;
+	}
+
+	/* Unconditionally unlock on close */
+	mctp_i2c_unlock_reset(midev);
+
+	/* Remove the netdev from the parent i2c client. */
+	spin_lock_irqsave(&mcli->sel_lock, flags);
+	list_del(&midev->list);
+	if (mcli->sel == midev) {
+		struct mctp_i2c_dev *first;
+
+		first = list_first_entry_or_null(&mcli->devs, struct mctp_i2c_dev, list);
+		__mctp_i2c_device_select(mcli, first);
+	}
+	spin_unlock_irqrestore(&mcli->sel_lock, flags);
+
+	skb_queue_purge(&midev->tx_queue);
+	put_device(&midev->adapter->dev);
+	put_device(&mcli->client->dev);
+}
+
+/* Stops, unregisters, and frees midev */
+static void mctp_i2c_unregister(struct mctp_i2c_dev *midev)
+{
+	unsigned long flags;
+
+	/* Stop tx thread prior to unregister, it uses netif_() functions */
+	kthread_stop(midev->tx_thread);
+	midev->tx_thread = NULL;
+
+	/* Prevent any new rx in mctp_i2c_recv(), let any pending work finish */
+	spin_lock_irqsave(&midev->lock, flags);
+	midev->allow_rx = false;
+	spin_unlock_irqrestore(&midev->lock, flags);
+	wait_for_completion(&midev->rx_done);
+
+	mctp_unregister_netdev(midev->ndev);
+	/* midev has been freed now by mctp_i2c_ndo_uninit callback */
+
+	free_netdev(midev->ndev);
+}
+
+static void mctp_i2c_ndo_uninit(struct net_device *dev)
+{
+	struct mctp_i2c_dev *midev = netdev_priv(dev);
+
+	/* Perform cleanup here to ensure that mcli->sel isn't holding
+	 * a reference that would prevent unregister_netdevice()
+	 * from completing.
+	 */
+	mctp_i2c_midev_free(midev);
+}
+
+static int mctp_i2c_ndo_open(struct net_device *dev)
+{
+	struct mctp_i2c_dev *midev = netdev_priv(dev);
+	unsigned long flags;
+
+	/* i2c rx handler can only pass packets once the netdev is registered */
+	spin_lock_irqsave(&midev->lock, flags);
+	midev->allow_rx = true;
+	spin_unlock_irqrestore(&midev->lock, flags);
+
+	return 0;
+}
+
+static int mctp_i2c_add_netdev(struct mctp_i2c_client *mcli,
+			       struct i2c_adapter *adap)
+{
+	struct mctp_i2c_dev *midev = NULL;
+	struct net_device *ndev = NULL;
+	struct i2c_adapter *root;
+	unsigned long flags;
+	char namebuf[30];
+	int rc;
+
+	root = mux_root_adapter(adap);
+	if (root != mcli->client->adapter) {
+		dev_err(&mcli->client->dev,
+			"I2C adapter %s is not a child bus of %s\n",
+			mcli->client->adapter->name, root->name);
+		return -EINVAL;
+	}
+
+	WARN_ON(!mutex_is_locked(&driver_clients_lock));
+	snprintf(namebuf, sizeof(namebuf), "mctpi2c%d", adap->nr);
+	ndev = alloc_netdev(sizeof(*midev), namebuf, NET_NAME_ENUM, mctp_i2c_net_setup);
+	if (!ndev) {
+		dev_err(&mcli->client->dev, "alloc netdev failed\n");
+		rc = -ENOMEM;
+		goto err;
+	}
+	dev_net_set(ndev, current->nsproxy->net_ns);
+	SET_NETDEV_DEV(ndev, &adap->dev);
+	dev_addr_set(ndev, &mcli->lladdr);
+
+	midev = mctp_i2c_midev_init(ndev, mcli, adap);
+	if (IS_ERR(midev)) {
+		rc = PTR_ERR(midev);
+		midev = NULL;
+		goto err;
+	}
+
+	rc = mctp_register_netdev(ndev, &mctp_i2c_mctp_ops);
+	if (rc < 0) {
+		dev_err(&mcli->client->dev,
+			"register netdev \"%s\" failed %d\n",
+			ndev->name, rc);
+		goto err;
+	}
+
+	spin_lock_irqsave(&midev->lock, flags);
+	midev->allow_rx = false;
+	spin_unlock_irqrestore(&midev->lock, flags);
+
+	return 0;
+err:
+	if (midev)
+		mctp_i2c_midev_free(midev);
+	if (ndev)
+		free_netdev(ndev);
+	return rc;
+}
+
+/* Removes any netdev for adap. mcli is the parent root i2c client */
+static void mctp_i2c_remove_netdev(struct mctp_i2c_client *mcli,
+				   struct i2c_adapter *adap)
+{
+	struct mctp_i2c_dev *midev = NULL, *m = NULL;
+	unsigned long flags;
+
+	WARN_ON(!mutex_is_locked(&driver_clients_lock));
+	spin_lock_irqsave(&mcli->sel_lock, flags);
+	/* List size is limited by number of MCTP netdevs on a single hardware bus */
+	list_for_each_entry(m, &mcli->devs, list)
+		if (m->adapter == adap) {
+			midev = m;
+			break;
+		}
+	spin_unlock_irqrestore(&mcli->sel_lock, flags);
+
+	if (midev)
+		mctp_i2c_unregister(midev);
+}
+
+/* Determines whether a device is an i2c adapter.
+ * Optionally returns the root i2c_adapter
+ */
+static struct i2c_adapter *mctp_i2c_get_adapter(struct device *dev,
+						struct i2c_adapter **ret_root)
+{
+	struct i2c_adapter *root, *adap;
+
+	if (dev->type != &i2c_adapter_type)
+		return NULL;
+	adap = to_i2c_adapter(dev);
+	root = mux_root_adapter(adap);
+	WARN_ONCE(!root, "MCTP I2C failed to find root adapter for %s\n",
+		  dev_name(dev));
+	if (!root)
+		return NULL;
+	if (ret_root)
+		*ret_root = root;
+	return adap;
+}
+
+/* Determines whether a device is an i2c adapter with the "mctp-controller"
+ * devicetree property set. If adap is not an OF node, returns match_no_of
+ */
+static bool mctp_i2c_adapter_match(struct i2c_adapter *adap, bool match_no_of)
+{
+	if (!adap->dev.of_node)
+		return match_no_of;
+	return of_property_read_bool(adap->dev.of_node, MCTP_I2C_OF_PROP);
+}
+
+/* Called for each existing i2c device (adapter or client) when a
+ * new mctp-i2c client is probed.
+ */
+static int mctp_i2c_client_try_attach(struct device *dev, void *data)
+{
+	struct i2c_adapter *adap = NULL, *root = NULL;
+	struct mctp_i2c_client *mcli = data;
+
+	adap = mctp_i2c_get_adapter(dev, &root);
+	if (!adap)
+		return 0;
+	if (mcli->client->adapter != root)
+		return 0;
+	/* Must either have mctp-controller property on the adapter, or
+	 * be a root adapter if it's non-devicetree
+	 */
+	if (!mctp_i2c_adapter_match(adap, adap == root))
+		return 0;
+
+	return mctp_i2c_add_netdev(mcli, adap);
+}
+
+static void mctp_i2c_notify_add(struct device *dev)
+{
+	struct mctp_i2c_client *mcli = NULL, *m = NULL;
+	struct i2c_adapter *root = NULL, *adap = NULL;
+	int rc;
+
+	adap = mctp_i2c_get_adapter(dev, &root);
+	if (!adap)
+		return;
+	/* Check for mctp-controller property on the adapter */
+	if (!mctp_i2c_adapter_match(adap, false))
+		return;
+
+	/* Find an existing mcli for adap's root */
+	mutex_lock(&driver_clients_lock);
+	list_for_each_entry(m, &driver_clients, list) {
+		if (m->client->adapter == root) {
+			mcli = m;
+			break;
+		}
+	}
+
+	if (mcli) {
+		rc = mctp_i2c_add_netdev(mcli, adap);
+		if (rc < 0)
+			dev_warn(dev, "Failed adding mctp-i2c net device\n");
+	}
+	mutex_unlock(&driver_clients_lock);
+}
+
+static void mctp_i2c_notify_del(struct device *dev)
+{
+	struct i2c_adapter *root = NULL, *adap = NULL;
+	struct mctp_i2c_client *mcli = NULL;
+
+	adap = mctp_i2c_get_adapter(dev, &root);
+	if (!adap)
+		return;
+
+	mutex_lock(&driver_clients_lock);
+	list_for_each_entry(mcli, &driver_clients, list) {
+		if (mcli->client->adapter == root) {
+			mctp_i2c_remove_netdev(mcli, adap);
+			break;
+		}
+	}
+	mutex_unlock(&driver_clients_lock);
+}
+
+static int mctp_i2c_probe(struct i2c_client *client)
+{
+	struct mctp_i2c_client *mcli = NULL;
+	int rc;
+
+	mutex_lock(&driver_clients_lock);
+	mcli = mctp_i2c_new_client(client);
+	if (IS_ERR(mcli)) {
+		rc = PTR_ERR(mcli);
+		mcli = NULL;
+		goto out;
+	} else {
+		list_add(&mcli->list, &driver_clients);
+	}
+
+	/* Add a netdev for adapters that have a 'mctp-controller' property */
+	i2c_for_each_dev(mcli, mctp_i2c_client_try_attach);
+	rc = 0;
+out:
+	mutex_unlock(&driver_clients_lock);
+	return rc;
+}
+
+static void mctp_i2c_remove(struct i2c_client *client)
+{
+	struct mctp_i2c_client *mcli = i2c_get_clientdata(client);
+	struct mctp_i2c_dev *midev = NULL, *tmp = NULL;
+
+	mutex_lock(&driver_clients_lock);
+	list_del(&mcli->list);
+	/* Remove all child adapter netdevs */
+	list_for_each_entry_safe(midev, tmp, &mcli->devs, list)
+		mctp_i2c_unregister(midev);
+
+	mctp_i2c_free_client(mcli);
+	mutex_unlock(&driver_clients_lock);
+}
+
+/* We look for a 'mctp-controller' property on I2C busses as they are
+ * added/deleted, creating/removing netdevs as required.
+ */
+static int mctp_i2c_notifier_call(struct notifier_block *nb,
+				  unsigned long action, void *data)
+{
+	struct device *dev = data;
+
+	switch (action) {
+	case BUS_NOTIFY_ADD_DEVICE:
+		mctp_i2c_notify_add(dev);
+		break;
+	case BUS_NOTIFY_DEL_DEVICE:
+		mctp_i2c_notify_del(dev);
+		break;
+	}
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block mctp_i2c_notifier = {
+	.notifier_call = mctp_i2c_notifier_call,
+};
+
+static const struct i2c_device_id mctp_i2c_id[] = {
+	{ "mctp-i2c-interface", 0 },
+	{},
+};
+MODULE_DEVICE_TABLE(i2c, mctp_i2c_id);
+
+static const struct of_device_id mctp_i2c_of_match[] = {
+	{ .compatible = "mctp-i2c-controller" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, mctp_i2c_of_match);
+
+static struct i2c_driver mctp_i2c_driver = {
+	.driver = {
+		.name = "mctp-i2c-interface",
+		.of_match_table = mctp_i2c_of_match,
+	},
+	.probe_new = mctp_i2c_probe,
+	.remove = mctp_i2c_remove,
+	.id_table = mctp_i2c_id,
+};
+
+static __init int mctp_i2c_mod_init(void)
+{
+	int rc;
+
+	pr_info("MCTP I2C interface driver\n");
+	rc = i2c_add_driver(&mctp_i2c_driver);
+	if (rc < 0)
+		return rc;
+	rc = bus_register_notifier(&i2c_bus_type, &mctp_i2c_notifier);
+	if (rc < 0) {
+		i2c_del_driver(&mctp_i2c_driver);
+		return rc;
+	}
+	return 0;
+}
+
+static __exit void mctp_i2c_mod_exit(void)
+{
+	int rc;
+
+	rc = bus_unregister_notifier(&i2c_bus_type, &mctp_i2c_notifier);
+	if (rc < 0)
+		pr_warn("MCTP I2C could not unregister notifier, %d\n", rc);
+	i2c_del_driver(&mctp_i2c_driver);
+}
+
+module_init(mctp_i2c_mod_init);
+module_exit(mctp_i2c_mod_exit);
+
+MODULE_DESCRIPTION("MCTP I2C device");
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Matt Johnston <matt@codeconstruct.com.au>");
diff --git a/drivers/net/mctp/mctp-serial.c b/drivers/net/mctp/mctp-serial.c
new file mode 100644
index 000000000..9f9eaf896
--- /dev/null
+++ b/drivers/net/mctp/mctp-serial.c
@@ -0,0 +1,524 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Management Component Transport Protocol (MCTP) - serial transport
+ * binding. This driver is an implementation of the DMTF specificiation
+ * "DSP0253 - Management Component Transport Protocol (MCTP) Serial Transport
+ * Binding", available at:
+ *
+ *  https://www.dmtf.org/sites/default/files/standards/documents/DSP0253_1.0.0.pdf
+ *
+ * This driver provides DSP0253-type MCTP-over-serial transport using a Linux
+ * tty device, by setting the N_MCTP line discipline on the tty.
+ *
+ * Copyright (c) 2021 Code Construct
+ */
+
+#include <linux/idr.h>
+#include <linux/if_arp.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/tty.h>
+#include <linux/workqueue.h>
+#include <linux/crc-ccitt.h>
+
+#include <linux/mctp.h>
+#include <net/mctp.h>
+#include <net/pkt_sched.h>
+
+#define MCTP_SERIAL_MTU		68 /* base mtu (64) + mctp header */
+#define MCTP_SERIAL_FRAME_MTU	(MCTP_SERIAL_MTU + 6) /* + serial framing */
+
+#define MCTP_SERIAL_VERSION	0x1 /* DSP0253 defines a single version: 1 */
+
+#define BUFSIZE			MCTP_SERIAL_FRAME_MTU
+
+#define BYTE_FRAME		0x7e
+#define BYTE_ESC		0x7d
+
+#define FCS_INIT		0xffff
+
+static DEFINE_IDA(mctp_serial_ida);
+
+enum mctp_serial_state {
+	STATE_IDLE,
+	STATE_START,
+	STATE_HEADER,
+	STATE_DATA,
+	STATE_ESCAPE,
+	STATE_TRAILER,
+	STATE_DONE,
+	STATE_ERR,
+};
+
+struct mctp_serial {
+	struct net_device	*netdev;
+	struct tty_struct	*tty;
+
+	int			idx;
+
+	/* protects our rx & tx state machines; held during both paths */
+	spinlock_t		lock;
+
+	struct work_struct	tx_work;
+	enum mctp_serial_state	txstate, rxstate;
+	u16			txfcs, rxfcs, rxfcs_rcvd;
+	unsigned int		txlen, rxlen;
+	unsigned int		txpos, rxpos;
+	unsigned char		txbuf[BUFSIZE],
+				rxbuf[BUFSIZE];
+};
+
+static bool needs_escape(unsigned char c)
+{
+	return c == BYTE_ESC || c == BYTE_FRAME;
+}
+
+static int next_chunk_len(struct mctp_serial *dev)
+{
+	int i;
+
+	/* either we have no bytes to send ... */
+	if (dev->txpos == dev->txlen)
+		return 0;
+
+	/* ... or the next byte to send is an escaped byte; requiring a
+	 * single-byte chunk...
+	 */
+	if (needs_escape(dev->txbuf[dev->txpos]))
+		return 1;
+
+	/* ... or we have one or more bytes up to the next escape - this chunk
+	 * will be those non-escaped bytes, and does not include the escaped
+	 * byte.
+	 */
+	for (i = 1; i + dev->txpos + 1 < dev->txlen; i++) {
+		if (needs_escape(dev->txbuf[dev->txpos + i + 1]))
+			break;
+	}
+
+	return i;
+}
+
+static int write_chunk(struct mctp_serial *dev, unsigned char *buf, int len)
+{
+	return dev->tty->ops->write(dev->tty, buf, len);
+}
+
+static void mctp_serial_tx_work(struct work_struct *work)
+{
+	struct mctp_serial *dev = container_of(work, struct mctp_serial,
+					       tx_work);
+	unsigned char c, buf[3];
+	unsigned long flags;
+	int len, txlen;
+
+	spin_lock_irqsave(&dev->lock, flags);
+
+	/* txstate represents the next thing to send */
+	switch (dev->txstate) {
+	case STATE_START:
+		dev->txpos = 0;
+		fallthrough;
+	case STATE_HEADER:
+		buf[0] = BYTE_FRAME;
+		buf[1] = MCTP_SERIAL_VERSION;
+		buf[2] = dev->txlen;
+
+		if (!dev->txpos)
+			dev->txfcs = crc_ccitt(FCS_INIT, buf + 1, 2);
+
+		txlen = write_chunk(dev, buf + dev->txpos, 3 - dev->txpos);
+		if (txlen <= 0) {
+			dev->txstate = STATE_ERR;
+		} else {
+			dev->txpos += txlen;
+			if (dev->txpos == 3) {
+				dev->txstate = STATE_DATA;
+				dev->txpos = 0;
+			}
+		}
+		break;
+
+	case STATE_ESCAPE:
+		buf[0] = dev->txbuf[dev->txpos] & ~0x20;
+		txlen = write_chunk(dev, buf, 1);
+		if (txlen <= 0) {
+			dev->txstate = STATE_ERR;
+		} else {
+			dev->txpos += txlen;
+			if (dev->txpos == dev->txlen) {
+				dev->txstate = STATE_TRAILER;
+				dev->txpos = 0;
+			}
+		}
+
+		break;
+
+	case STATE_DATA:
+		len = next_chunk_len(dev);
+		if (len) {
+			c = dev->txbuf[dev->txpos];
+			if (len == 1 && needs_escape(c)) {
+				buf[0] = BYTE_ESC;
+				buf[1] = c & ~0x20;
+				dev->txfcs = crc_ccitt_byte(dev->txfcs, c);
+				txlen = write_chunk(dev, buf, 2);
+				if (txlen == 2)
+					dev->txpos++;
+				else if (txlen == 1)
+					dev->txstate = STATE_ESCAPE;
+				else
+					dev->txstate = STATE_ERR;
+			} else {
+				txlen = write_chunk(dev,
+						    dev->txbuf + dev->txpos,
+						    len);
+				if (txlen <= 0) {
+					dev->txstate = STATE_ERR;
+				} else {
+					dev->txfcs = crc_ccitt(dev->txfcs,
+							       dev->txbuf +
+							       dev->txpos,
+							       txlen);
+					dev->txpos += txlen;
+				}
+			}
+			if (dev->txstate == STATE_DATA &&
+			    dev->txpos == dev->txlen) {
+				dev->txstate = STATE_TRAILER;
+				dev->txpos = 0;
+			}
+			break;
+		}
+		dev->txstate = STATE_TRAILER;
+		dev->txpos = 0;
+		fallthrough;
+
+	case STATE_TRAILER:
+		buf[0] = dev->txfcs >> 8;
+		buf[1] = dev->txfcs & 0xff;
+		buf[2] = BYTE_FRAME;
+		txlen = write_chunk(dev, buf + dev->txpos, 3 - dev->txpos);
+		if (txlen <= 0) {
+			dev->txstate = STATE_ERR;
+		} else {
+			dev->txpos += txlen;
+			if (dev->txpos == 3) {
+				dev->txstate = STATE_DONE;
+				dev->txpos = 0;
+			}
+		}
+		break;
+	default:
+		netdev_err_once(dev->netdev, "invalid tx state %d\n",
+				dev->txstate);
+	}
+
+	if (dev->txstate == STATE_DONE) {
+		dev->netdev->stats.tx_packets++;
+		dev->netdev->stats.tx_bytes += dev->txlen;
+		dev->txlen = 0;
+		dev->txpos = 0;
+		clear_bit(TTY_DO_WRITE_WAKEUP, &dev->tty->flags);
+		dev->txstate = STATE_IDLE;
+		spin_unlock_irqrestore(&dev->lock, flags);
+
+		netif_wake_queue(dev->netdev);
+	} else {
+		spin_unlock_irqrestore(&dev->lock, flags);
+	}
+}
+
+static netdev_tx_t mctp_serial_tx(struct sk_buff *skb, struct net_device *ndev)
+{
+	struct mctp_serial *dev = netdev_priv(ndev);
+	unsigned long flags;
+
+	WARN_ON(dev->txstate != STATE_IDLE);
+
+	if (skb->len > MCTP_SERIAL_MTU) {
+		dev->netdev->stats.tx_dropped++;
+		goto out;
+	}
+
+	spin_lock_irqsave(&dev->lock, flags);
+	netif_stop_queue(dev->netdev);
+	skb_copy_bits(skb, 0, dev->txbuf, skb->len);
+	dev->txpos = 0;
+	dev->txlen = skb->len;
+	dev->txstate = STATE_START;
+	spin_unlock_irqrestore(&dev->lock, flags);
+
+	set_bit(TTY_DO_WRITE_WAKEUP, &dev->tty->flags);
+	schedule_work(&dev->tx_work);
+
+out:
+	kfree_skb(skb);
+	return NETDEV_TX_OK;
+}
+
+static void mctp_serial_tty_write_wakeup(struct tty_struct *tty)
+{
+	struct mctp_serial *dev = tty->disc_data;
+
+	schedule_work(&dev->tx_work);
+}
+
+static void mctp_serial_rx(struct mctp_serial *dev)
+{
+	struct mctp_skb_cb *cb;
+	struct sk_buff *skb;
+
+	if (dev->rxfcs != dev->rxfcs_rcvd) {
+		dev->netdev->stats.rx_dropped++;
+		dev->netdev->stats.rx_crc_errors++;
+		return;
+	}
+
+	skb = netdev_alloc_skb(dev->netdev, dev->rxlen);
+	if (!skb) {
+		dev->netdev->stats.rx_dropped++;
+		return;
+	}
+
+	skb->protocol = htons(ETH_P_MCTP);
+	skb_put_data(skb, dev->rxbuf, dev->rxlen);
+	skb_reset_network_header(skb);
+
+	cb = __mctp_cb(skb);
+	cb->halen = 0;
+
+	netif_rx(skb);
+	dev->netdev->stats.rx_packets++;
+	dev->netdev->stats.rx_bytes += dev->rxlen;
+}
+
+static void mctp_serial_push_header(struct mctp_serial *dev, unsigned char c)
+{
+	switch (dev->rxpos) {
+	case 0:
+		if (c == BYTE_FRAME)
+			dev->rxpos++;
+		else
+			dev->rxstate = STATE_ERR;
+		break;
+	case 1:
+		if (c == MCTP_SERIAL_VERSION) {
+			dev->rxpos++;
+			dev->rxfcs = crc_ccitt_byte(FCS_INIT, c);
+		} else {
+			dev->rxstate = STATE_ERR;
+		}
+		break;
+	case 2:
+		if (c > MCTP_SERIAL_FRAME_MTU) {
+			dev->rxstate = STATE_ERR;
+		} else {
+			dev->rxlen = c;
+			dev->rxpos = 0;
+			dev->rxstate = STATE_DATA;
+			dev->rxfcs = crc_ccitt_byte(dev->rxfcs, c);
+		}
+		break;
+	}
+}
+
+static void mctp_serial_push_trailer(struct mctp_serial *dev, unsigned char c)
+{
+	switch (dev->rxpos) {
+	case 0:
+		dev->rxfcs_rcvd = c << 8;
+		dev->rxpos++;
+		break;
+	case 1:
+		dev->rxfcs_rcvd |= c;
+		dev->rxpos++;
+		break;
+	case 2:
+		if (c != BYTE_FRAME) {
+			dev->rxstate = STATE_ERR;
+		} else {
+			mctp_serial_rx(dev);
+			dev->rxlen = 0;
+			dev->rxpos = 0;
+			dev->rxstate = STATE_IDLE;
+		}
+		break;
+	}
+}
+
+static void mctp_serial_push(struct mctp_serial *dev, unsigned char c)
+{
+	switch (dev->rxstate) {
+	case STATE_IDLE:
+		dev->rxstate = STATE_HEADER;
+		fallthrough;
+	case STATE_HEADER:
+		mctp_serial_push_header(dev, c);
+		break;
+
+	case STATE_ESCAPE:
+		c |= 0x20;
+		fallthrough;
+	case STATE_DATA:
+		if (dev->rxstate != STATE_ESCAPE && c == BYTE_ESC) {
+			dev->rxstate = STATE_ESCAPE;
+		} else {
+			dev->rxfcs = crc_ccitt_byte(dev->rxfcs, c);
+			dev->rxbuf[dev->rxpos] = c;
+			dev->rxpos++;
+			dev->rxstate = STATE_DATA;
+			if (dev->rxpos == dev->rxlen) {
+				dev->rxpos = 0;
+				dev->rxstate = STATE_TRAILER;
+			}
+		}
+		break;
+
+	case STATE_TRAILER:
+		mctp_serial_push_trailer(dev, c);
+		break;
+
+	case STATE_ERR:
+		if (c == BYTE_FRAME)
+			dev->rxstate = STATE_IDLE;
+		break;
+
+	default:
+		netdev_err_once(dev->netdev, "invalid rx state %d\n",
+				dev->rxstate);
+	}
+}
+
+static void mctp_serial_tty_receive_buf(struct tty_struct *tty,
+					const unsigned char *c,
+					const char *f, int len)
+{
+	struct mctp_serial *dev = tty->disc_data;
+	int i;
+
+	if (!netif_running(dev->netdev))
+		return;
+
+	/* we don't (currently) use the flag bytes, just data. */
+	for (i = 0; i < len; i++)
+		mctp_serial_push(dev, c[i]);
+}
+
+static void mctp_serial_uninit(struct net_device *ndev)
+{
+	struct mctp_serial *dev = netdev_priv(ndev);
+
+	cancel_work_sync(&dev->tx_work);
+}
+
+static const struct net_device_ops mctp_serial_netdev_ops = {
+	.ndo_start_xmit = mctp_serial_tx,
+	.ndo_uninit = mctp_serial_uninit,
+};
+
+static void mctp_serial_setup(struct net_device *ndev)
+{
+	ndev->type = ARPHRD_MCTP;
+
+	/* we limit at the fixed MTU, which is also the MCTP-standard
+	 * baseline MTU, so is also our minimum
+	 */
+	ndev->mtu = MCTP_SERIAL_MTU;
+	ndev->max_mtu = MCTP_SERIAL_MTU;
+	ndev->min_mtu = MCTP_SERIAL_MTU;
+
+	ndev->hard_header_len = 0;
+	ndev->addr_len = 0;
+	ndev->tx_queue_len = DEFAULT_TX_QUEUE_LEN;
+	ndev->flags = IFF_NOARP;
+	ndev->netdev_ops = &mctp_serial_netdev_ops;
+	ndev->needs_free_netdev = true;
+}
+
+static int mctp_serial_open(struct tty_struct *tty)
+{
+	struct mctp_serial *dev;
+	struct net_device *ndev;
+	char name[32];
+	int idx, rc;
+
+	if (!capable(CAP_NET_ADMIN))
+		return -EPERM;
+
+	if (!tty->ops->write)
+		return -EOPNOTSUPP;
+
+	idx = ida_alloc(&mctp_serial_ida, GFP_KERNEL);
+	if (idx < 0)
+		return idx;
+
+	snprintf(name, sizeof(name), "mctpserial%d", idx);
+	ndev = alloc_netdev(sizeof(*dev), name, NET_NAME_ENUM,
+			    mctp_serial_setup);
+	if (!ndev) {
+		rc = -ENOMEM;
+		goto free_ida;
+	}
+
+	dev = netdev_priv(ndev);
+	dev->idx = idx;
+	dev->tty = tty;
+	dev->netdev = ndev;
+	dev->txstate = STATE_IDLE;
+	dev->rxstate = STATE_IDLE;
+	spin_lock_init(&dev->lock);
+	INIT_WORK(&dev->tx_work, mctp_serial_tx_work);
+
+	rc = register_netdev(ndev);
+	if (rc)
+		goto free_netdev;
+
+	tty->receive_room = 64 * 1024;
+	tty->disc_data = dev;
+
+	return 0;
+
+free_netdev:
+	free_netdev(ndev);
+
+free_ida:
+	ida_free(&mctp_serial_ida, idx);
+	return rc;
+}
+
+static void mctp_serial_close(struct tty_struct *tty)
+{
+	struct mctp_serial *dev = tty->disc_data;
+	int idx = dev->idx;
+
+	unregister_netdev(dev->netdev);
+	ida_free(&mctp_serial_ida, idx);
+}
+
+static struct tty_ldisc_ops mctp_ldisc = {
+	.owner		= THIS_MODULE,
+	.num		= N_MCTP,
+	.name		= "mctp",
+	.open		= mctp_serial_open,
+	.close		= mctp_serial_close,
+	.receive_buf	= mctp_serial_tty_receive_buf,
+	.write_wakeup	= mctp_serial_tty_write_wakeup,
+};
+
+static int __init mctp_serial_init(void)
+{
+	return tty_register_ldisc(&mctp_ldisc);
+}
+
+static void __exit mctp_serial_exit(void)
+{
+	tty_unregister_ldisc(&mctp_ldisc);
+}
+
+module_init(mctp_serial_init);
+module_exit(mctp_serial_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Jeremy Kerr <jk@codeconstruct.com.au>");
+MODULE_DESCRIPTION("MCTP Serial transport");