@@ -47,6 +47,19 @@ config MCTP_TRANSPORT_I3C
 	  A MCTP protocol network device is created for each I3C bus
 	  having a "mctp-controller" devicetree property.
 
+config MCTP_TRANSPORT_PCC
+	tristate "MCTP PCC transport"
+	select ACPI
+	help
+	  Provides a driver to access MCTP devices over PCC transport,
+	  A MCTP protocol network device is created via ACPI for each
+	  entry in the DST/SDST that matches the identifier. The Platform
+	  commuinucation channels are selected from the corresponding
+	  entries in the PCCT.
+
+	  Say y here if you need to connect to MCTP endpoints over PCC. To
+	  compile as a module, use m; the module will be called mctp-pcc.
+
 endmenu
 
 endif

@@ -1,3 +1,4 @@
+obj-$(CONFIG_MCTP_TRANSPORT_PCC) += mctp-pcc.o
 obj-$(CONFIG_MCTP_SERIAL) += mctp-serial.o
 obj-$(CONFIG_MCTP_TRANSPORT_I2C) += mctp-i2c.o
 obj-$(CONFIG_MCTP_TRANSPORT_I3C) += mctp-i3c.o

@@ -0,0 +1,332 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * mctp-pcc.c - Driver for MCTP over PCC.
+ * Copyright (c) 2024, Ampere Computing LLC
+ */
+
+/* Implelmentation of MCTP over PCC DMTF Specification 256
+ * https://www.dmtf.org/sites/default/files/standards/documents/DSP0256_2.0.0WIP50.pdf
+ */
+
+#include <linux/acpi.h>
+#include <linux/if_arp.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/netdevice.h>
+#include <linux/platform_device.h>
+#include <linux/string.h>
+
+#include <acpi/acpi_bus.h>
+#include <acpi/acpi_drivers.h>
+#include <acpi/acrestyp.h>
+#include <acpi/actbl.h>
+#include <net/mctp.h>
+#include <net/mctpdevice.h>
+#include <acpi/pcc.h>
+
+#define MCTP_PAYLOAD_LENGTH     256
+#define MCTP_CMD_LENGTH         4
+#define MCTP_PCC_VERSION        0x1 /* DSP0253 defines a single version: 1 */
+#define MCTP_SIGNATURE          "MCTP"
+#define MCTP_SIGNATURE_LENGTH   (sizeof(MCTP_SIGNATURE) - 1)
+#define MCTP_HEADER_LENGTH      12
+#define MCTP_MIN_MTU            68
+#define PCC_MAGIC               0x50434300
+#define PCC_HEADER_FLAG_REQ_INT 0x1
+#define PCC_HEADER_FLAGS        PCC_HEADER_FLAG_REQ_INT
+#define PCC_DWORD_TYPE          0x0c
+
+struct mctp_pcc_hdr {
+	u32 signature;
+	u32 flags;
+	u32 length;
+	char mctp_signature[MCTP_SIGNATURE_LENGTH];
+};
+
+struct mctp_pcc_mailbox {
+	u32 index;
+	struct pcc_mbox_chan *chan;
+	struct mbox_client client;
+	void __iomem *addr;
+};
+
+struct mctp_pcc_hw_addr {
+	__be32 parent_id;
+	__be16 inbox_id;
+	__be16 outbox_id;
+};
+
+/* The netdev structure. One of these per PCC adapter. */
+struct mctp_pcc_ndev {
+	/* spinlock to serialize access to PCC outbox buffer and registers
+	 * Note that what PCC calls registers are memory locations, not CPU
+	 * Registers.  They include the fields used to synchronize access
+	 * between the OS and remote endpoints.
+	 *
+	 * Only the Outbox needs a spinlock, to prevent multiple
+	 * sent packets triggering multiple attempts to over write
+	 * the outbox.  The Inbox buffer is controlled by the remote
+	 * service and a spinlock would have no effect.
+	 */
+	spinlock_t lock;
+	struct mctp_dev mdev;
+	struct acpi_device *acpi_device;
+	struct mctp_pcc_mailbox inbox;
+	struct mctp_pcc_mailbox outbox;
+};
+
+static void mctp_pcc_client_rx_callback(struct mbox_client *c, void *buffer)
+{
+	struct mctp_pcc_ndev *mctp_pcc_dev;
+	struct mctp_pcc_hdr mctp_pcc_hdr;
+	struct mctp_skb_cb *cb;
+	struct sk_buff *skb;
+	void *skb_buf;
+	u32 data_len;
+
+	mctp_pcc_dev = container_of(c, struct mctp_pcc_ndev, inbox.client);
+	memcpy_fromio(&mctp_pcc_hdr, mctp_pcc_dev->inbox.addr,
+		      sizeof(struct mctp_pcc_hdr));
+	data_len = mctp_pcc_hdr.length + MCTP_HEADER_LENGTH;
+
+	if (data_len > mctp_pcc_dev->mdev.dev->mtu) {
+		mctp_pcc_dev->mdev.dev->stats.rx_dropped++;
+		return;
+	}
+
+	skb = netdev_alloc_skb(mctp_pcc_dev->mdev.dev, data_len);
+	if (!skb) {
+		mctp_pcc_dev->mdev.dev->stats.rx_dropped++;
+		return;
+	}
+	mctp_pcc_dev->mdev.dev->stats.rx_packets++;
+	mctp_pcc_dev->mdev.dev->stats.rx_bytes += data_len;
+	skb->protocol = htons(ETH_P_MCTP);
+	skb_buf = skb_put(skb, data_len);
+	memcpy_fromio(skb_buf, mctp_pcc_dev->inbox.addr, data_len);
+
+	skb_reset_mac_header(skb);
+	skb_pull(skb, sizeof(struct mctp_pcc_hdr));
+	skb_reset_network_header(skb);
+	cb = __mctp_cb(skb);
+	cb->halen = 0;
+	netif_rx(skb);
+}
+
+static netdev_tx_t mctp_pcc_tx(struct sk_buff *skb, struct net_device *ndev)
+{
+	struct mctp_pcc_ndev *mpnd = netdev_priv(ndev);
+	struct mctp_pcc_hdr mctp_pcc_header;
+	void __iomem *buffer;
+	unsigned long flags;
+
+	ndev->stats.tx_bytes += skb->len;
+	ndev->stats.tx_packets++;
+
+	spin_lock_irqsave(&mpnd->lock, flags);
+	buffer = mpnd->outbox.addr;
+	mctp_pcc_header.signature = PCC_MAGIC | mpnd->outbox.index;
+	mctp_pcc_header.flags = PCC_HEADER_FLAGS;
+	memcpy(mctp_pcc_header.mctp_signature, MCTP_SIGNATURE,
+	       MCTP_SIGNATURE_LENGTH);
+	mctp_pcc_header.length = skb->len + MCTP_SIGNATURE_LENGTH;
+	memcpy_toio(buffer, &mctp_pcc_header, sizeof(struct mctp_pcc_hdr));
+	memcpy_toio(buffer + sizeof(struct mctp_pcc_hdr), skb->data, skb->len);
+	mpnd->outbox.chan->mchan->mbox->ops->send_data(mpnd->outbox.chan->mchan,
+						    NULL);
+	spin_unlock_irqrestore(&mpnd->lock, flags);
+
+	dev_consume_skb_any(skb);
+	return NETDEV_TX_OK;
+}
+
+static void
+mctp_pcc_net_stats(struct net_device *net_dev,
+		   struct rtnl_link_stats64 *stats)
+{
+	stats->rx_errors = 0;
+	stats->rx_packets = net_dev->stats.rx_packets;
+	stats->tx_packets = net_dev->stats.tx_packets;
+	stats->rx_dropped = 0;
+	stats->tx_bytes = net_dev->stats.tx_bytes;
+	stats->rx_bytes = net_dev->stats.rx_bytes;
+}
+
+static const struct net_device_ops mctp_pcc_netdev_ops = {
+	.ndo_start_xmit = mctp_pcc_tx,
+	.ndo_get_stats64 = mctp_pcc_net_stats,
+};
+
+static void  mctp_pcc_setup(struct net_device *ndev)
+{
+	ndev->type = ARPHRD_MCTP;
+	ndev->hard_header_len = 0;
+	ndev->tx_queue_len = 0;
+	ndev->flags = IFF_NOARP;
+	ndev->netdev_ops = &mctp_pcc_netdev_ops;
+	ndev->needs_free_netdev = true;
+}
+
+struct mctp_pcc_lookup_context {
+	int index;
+	u32 inbox_index;
+	u32 outbox_index;
+};
+
+static acpi_status lookup_pcct_indices(struct acpi_resource *ares,
+				       void *context)
+{
+	struct  mctp_pcc_lookup_context *luc = context;
+	struct acpi_resource_address32 *addr;
+
+	switch (ares->type) {
+	case PCC_DWORD_TYPE:
+		break;
+	default:
+		return AE_OK;
+	}
+
+	addr = ACPI_CAST_PTR(struct acpi_resource_address32, &ares->data);
+	switch (luc->index) {
+	case 0:
+		luc->outbox_index = addr[0].address.minimum;
+		break;
+	case 1:
+		luc->inbox_index = addr[0].address.minimum;
+		break;
+	}
+	luc->index++;
+	return AE_OK;
+}
+
+static void mctp_cleanup_netdev(void *data)
+{
+	struct net_device *ndev = data;
+
+	mctp_unregister_netdev(ndev);
+}
+
+static void mctp_cleanup_channel(void *data)
+{
+	struct pcc_mbox_chan *chan = data;
+
+	pcc_mbox_free_channel(chan);
+}
+
+static int mctp_pcc_initialize_mailbox(struct device *dev,
+				       struct mctp_pcc_mailbox *box, u32 index)
+{
+	pr_info("index = %u", index);
+	box->index = index;
+	box->chan = pcc_mbox_request_channel(&box->client, index);
+	if (IS_ERR(box->chan))
+		return PTR_ERR(box->chan);
+	box->addr = devm_ioremap(dev, box->chan->shmem_base_addr,
+				 box->chan->shmem_size);
+	if (!box->addr)
+		return -EINVAL;
+	return devm_add_action_or_reset(dev, mctp_cleanup_channel, box->chan);
+}
+
+static int mctp_pcc_driver_add(struct acpi_device *acpi_dev)
+{
+	struct mctp_pcc_lookup_context context = {0, 0, 0};
+	struct mctp_pcc_hw_addr mctp_pcc_hw_addr;
+	struct mctp_pcc_ndev *mctp_pcc_ndev;
+	struct device *dev = &acpi_dev->dev;
+	struct net_device *ndev;
+	acpi_handle dev_handle;
+	acpi_status status;
+	int mctp_pcc_mtu;
+	char name[32];
+	int rc;
+
+	dev_dbg(dev, "Adding mctp_pcc device for HID  %s\n",
+		acpi_device_hid(acpi_dev));
+	dev_handle = acpi_device_handle(acpi_dev);
+	status = acpi_walk_resources(dev_handle, "_CRS", lookup_pcct_indices,
+				     &context);
+	if (!ACPI_SUCCESS(status)) {
+		dev_err(dev, "FAILURE to lookup PCC indexes from CRS");
+		return -EINVAL;
+	}
+
+	//inbox initialization
+	snprintf(name, sizeof(name), "mctpipcc%d", context.inbox_index);
+	ndev = alloc_netdev(sizeof(struct mctp_pcc_ndev), name, NET_NAME_ENUM,
+			    mctp_pcc_setup);
+	if (!ndev)
+		return -ENOMEM;
+
+	mctp_pcc_ndev = netdev_priv(ndev);
+	rc =  devm_add_action_or_reset(dev, mctp_cleanup_netdev, ndev);
+	if (rc)
+		goto cleanup_netdev;
+	spin_lock_init(&mctp_pcc_ndev->lock);
+
+	rc = mctp_pcc_initialize_mailbox(dev, &mctp_pcc_ndev->inbox,
+					 context.inbox_index);
+	if (rc)
+		goto cleanup_netdev;
+	mctp_pcc_ndev->inbox.client.rx_callback = mctp_pcc_client_rx_callback;
+
+	//outbox initialization
+	rc = mctp_pcc_initialize_mailbox(dev, &mctp_pcc_ndev->outbox,
+					 context.outbox_index);
+	if (rc)
+		goto cleanup_netdev;
+
+	mctp_pcc_hw_addr.parent_id = cpu_to_be32(0);
+	mctp_pcc_hw_addr.inbox_id = cpu_to_be16(context.inbox_index);
+	mctp_pcc_hw_addr.outbox_id = cpu_to_be16(context.outbox_index);
+	ndev->addr_len = sizeof(mctp_pcc_hw_addr);
+	dev_addr_set(ndev, (const u8 *)&mctp_pcc_hw_addr);
+
+	mctp_pcc_ndev->acpi_device = acpi_dev;
+	mctp_pcc_ndev->inbox.client.dev = dev;
+	mctp_pcc_ndev->outbox.client.dev = dev;
+	mctp_pcc_ndev->mdev.dev = ndev;
+	acpi_dev->driver_data = mctp_pcc_ndev;
+
+	/* There is no clean way to pass the MTU to the callback function
+	 * used for registration, so set the values ahead of time.
+	 */
+	mctp_pcc_mtu = mctp_pcc_ndev->outbox.chan->shmem_size -
+		sizeof(struct mctp_pcc_hdr);
+	ndev->mtu = MCTP_MIN_MTU;
+	ndev->max_mtu = mctp_pcc_mtu;
+	ndev->min_mtu = MCTP_MIN_MTU;
+
+	/* ndev needs to be freed before the iomemory (mapped above) gets
+	 * unmapped,  devm resources get freed in reverse to the order they
+	 * are added.
+	 */
+	rc = register_netdev(ndev);
+	return rc;
+cleanup_netdev:
+	free_netdev(ndev);
+	return rc;
+}
+
+static const struct acpi_device_id mctp_pcc_device_ids[] = {
+	{ "DMT0001"},
+	{}
+};
+
+static struct acpi_driver mctp_pcc_driver = {
+	.name = "mctp_pcc",
+	.class = "Unknown",
+	.ids = mctp_pcc_device_ids,
+	.ops = {
+		.add = mctp_pcc_driver_add,
+	},
+};
+
+module_acpi_driver(mctp_pcc_driver);
+
+MODULE_DEVICE_TABLE(acpi, mctp_pcc_device_ids);
+
+MODULE_DESCRIPTION("MCTP PCC ACPI device");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Adam Young <admiyo@os.amperecomputing.com>");