Merge branch 'i3c-mctp-net-driver'

Matt Johnston says:

====================
I3C MCTP net driver

This series adds an I3C transport for the kernel's MCTP network
protocol. MCTP is a communication protocol between system components
(BMCs, drives, NICs etc), with higher level protocols such as NVMe-MI or
PLDM built on top of it (in userspace). It runs over various transports
such as I2C, PCIe, or I3C.

The mctp-i3c driver follows a similar approach to the kernel's existing
mctp-i2c driver, creating a "mctpi3cX" network interface for each
numbered I3C bus. Busses opt in to support by adding a "mctp-controller"
property to the devicetree:

&i3c0 {
        mctp-controller;
}

The driver will bind to MCTP class devices (DCR 0xCC) that are on a
supported I3C bus. Each bus is represented by a `struct mctp_i3c_bus`
that keeps state for the network device. An individual I3C device
(struct mctp_i3c_device) performs operations using the "parent"
mctp_i3c_bus object. The I3C notify/enumeration patch is needed so that
the mctp-i3c driver can handle creating/removing mctp_i3c_bus objects as
required.

The mctp-i3c driver is using the Provisioned ID as an identifier for
target I3C devices (the neighbour address), as that will be more stable
than the I3C dynamic address. The driver internally translates that to a
dynamic address for bus operations.

The driver has been tested using an AST2600 platform. A remote endpoint
has been tested against QEMU, as well as using the target mode support
in Aspeed's vendor tree.

I3C maintainers have acked merging this through net-next tree.
====================

Link: https://lore.kernel.org/r/20231013040628.354323-1-matt@codeconstruct.com.au
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/devicetree/bindings/i3c/i3c.yaml

@@ -55,6 +55,12 @@ properties:
 
       May not be supported by all controllers.
 
+  mctp-controller:
+    type: boolean
+    description: |
+      Indicates that the system is accessible via this bus as an endpoint for
+      MCTP over I3C transport.
+
 required:
   - "#address-cells"
   - "#size-cells"

drivers/i3c/master.c

@@ -22,6 +22,7 @@
 static DEFINE_IDR(i3c_bus_idr);
 static DEFINE_MUTEX(i3c_core_lock);
 static int __i3c_first_dynamic_bus_num;
+static BLOCKING_NOTIFIER_HEAD(i3c_bus_notifier);
 
 /**
  * i3c_bus_maintenance_lock - Lock the bus for a maintenance operation
@@ -453,6 +454,36 @@ static int i3c_bus_init(struct i3c_bus *i3cbus, struct device_node *np)
 	return 0;
 }
 
+void i3c_for_each_bus_locked(int (*fn)(struct i3c_bus *bus, void *data),
+			     void *data)
+{
+	struct i3c_bus *bus;
+	int id;
+
+	mutex_lock(&i3c_core_lock);
+	idr_for_each_entry(&i3c_bus_idr, bus, id)
+		fn(bus, data);
+	mutex_unlock(&i3c_core_lock);
+}
+EXPORT_SYMBOL_GPL(i3c_for_each_bus_locked);
+
+int i3c_register_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_register(&i3c_bus_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(i3c_register_notifier);
+
+int i3c_unregister_notifier(struct notifier_block *nb)
+{
+	return blocking_notifier_chain_unregister(&i3c_bus_notifier, nb);
+}
+EXPORT_SYMBOL_GPL(i3c_unregister_notifier);
+
+static void i3c_bus_notify(struct i3c_bus *bus, unsigned int action)
+{
+	blocking_notifier_call_chain(&i3c_bus_notifier, action, bus);
+}
+
 static const char * const i3c_bus_mode_strings[] = {
 	[I3C_BUS_MODE_PURE] = "pure",
 	[I3C_BUS_MODE_MIXED_FAST] = "mixed-fast",
@@ -2682,6 +2713,8 @@ int i3c_master_register(struct i3c_master_controller *master,
 	if (ret)
 		goto err_del_dev;
 
+	i3c_bus_notify(i3cbus, I3C_NOTIFY_BUS_ADD);
+
 	/*
 	 * We're done initializing the bus and the controller, we can now
 	 * register I3C devices discovered during the initial DAA.
@@ -2714,6 +2747,8 @@ EXPORT_SYMBOL_GPL(i3c_master_register);
  */
 void i3c_master_unregister(struct i3c_master_controller *master)
 {
+	i3c_bus_notify(&master->bus, I3C_NOTIFY_BUS_REMOVE);
+
 	i3c_master_i2c_adapter_cleanup(master);
 	i3c_master_unregister_i3c_devs(master);
 	i3c_master_bus_cleanup(master);

drivers/net/mctp/Kconfig

@@ -33,6 +33,15 @@ config MCTP_TRANSPORT_I2C
 	  from DMTF specification DSP0237. A MCTP protocol network device is
 	  created for each I2C bus that has been assigned a mctp-i2c device.
 
+config MCTP_TRANSPORT_I3C
+	tristate "MCTP I3C transport"
+	depends on I3C
+	help
+	  Provides a driver to access MCTP devices over I3C transport,
+	  from DMTF specification DSP0233.
+	  A MCTP protocol network device is created for each I3C bus
+	  having a "mctp-controller" devicetree property.
+
 endmenu
 
 endif

drivers/net/mctp/Makefile

@@ -1,2 +1,3 @@
 obj-$(CONFIG_MCTP_SERIAL) += mctp-serial.o
 obj-$(CONFIG_MCTP_TRANSPORT_I2C) += mctp-i2c.o
+obj-$(CONFIG_MCTP_TRANSPORT_I3C) += mctp-i3c.o

drivers/net/mctp/mctp-i3c.c

@@ -0,0 +1,755 @@
+// 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 <asm/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>");

include/linux/i3c/master.h

@@ -24,6 +24,12 @@
 
 struct i2c_client;
 
+/* notifier actions. notifier call data is the struct i3c_bus */
+enum {
+	I3C_NOTIFY_BUS_ADD,
+	I3C_NOTIFY_BUS_REMOVE,
+};
+
 struct i3c_master_controller;
 struct i3c_bus;
 struct i3c_device;
@@ -652,4 +658,9 @@ void i3c_master_queue_ibi(struct i3c_dev_desc *dev, struct i3c_ibi_slot *slot);
 
 struct i3c_ibi_slot *i3c_master_get_free_ibi_slot(struct i3c_dev_desc *dev);
 
+void i3c_for_each_bus_locked(int (*fn)(struct i3c_bus *bus, void *data),
+			     void *data);
+int i3c_register_notifier(struct notifier_block *nb);
+int i3c_unregister_notifier(struct notifier_block *nb);
+
 #endif /* I3C_MASTER_H */