Add support for IPMB driver

Support receiving IPMB requests on a Satellite MC from the BMC.
Once a response is ready, this driver will send back a response
to the BMC via the IPMB channel.

Signed-off-by: Asmaa Mnebhi <[e-mail]>
Acked-by: [e-mail]
Message-Id: <[e-mail]>
[Move the config option to outside the ipmi msghandler, as it's not
dependent on that. Fixed one small whitespace issue.]
Signed-off-by: Corey Minyard <[e-mail]>

Documentation/IPMB.txt

···
+==============================
+IPMB Driver for a Satellite MC
+==============================
+
+The Intelligent Platform Management Bus or IPMB, is an
+I2C bus that provides a standardized interconnection between
+different boards within a chassis. This interconnection is
+between the baseboard management (BMC) and chassis electronics.
+IPMB is also associated with the messaging protocol through the
+IPMB bus.
+
+The devices using the IPMB are usually management
+controllers that perform management functions such as servicing
+the front panel interface, monitoring the baseboard,
+hot-swapping disk drivers in the system chassis, etc...
+
+When an IPMB is implemented in the system, the BMC serves as
+a controller to give system software access to the IPMB. The BMC
+sends IPMI requests to a device (usually a Satellite Management
+Controller or Satellite MC) via IPMB and the device
+sends a response back to the BMC.
+
+For more information on IPMB and the format of an IPMB message,
+refer to the IPMB and IPMI specifications.
+
+IPMB driver for Satellite MC
+----------------------------
+
+ipmb-dev-int - This is the driver needed on a Satellite MC to
+receive IPMB messages from a BMC and send a response back.
+This driver works with the I2C driver and a userspace
+program such as OpenIPMI:
+
+1) It is an I2C slave backend driver. So, it defines a callback
+function to set the Satellite MC as an I2C slave.
+This callback function handles the received IPMI requests.
+
+2) It defines the read and write functions to enable a user
+space program (such as OpenIPMI) to communicate with the kernel.
+
+
+Load the IPMB driver
+--------------------
+
+The driver needs to be loaded at boot time or manually first.
+First, make sure you have the following in your config file:
+CONFIG_IPMB_DEVICE_INTERFACE=y
+
+1) If you want the driver to be loaded at boot time:
+
+a) Add this entry to your ACPI table, under the appropriate SMBus:
+
+Device (SMB0) // Example SMBus host controller
+{
+  Name (_HID, "<Vendor-Specific HID>") // Vendor-Specific HID
+  Name (_UID, 0) // Unique ID of particular host controller
+  :
+  :
+    Device (IPMB)
+    {
+      Name (_HID, "IPMB0001") // IPMB device interface
+      Name (_UID, 0) // Unique device identifier
+    }
+}
+
+b) Example for device tree:
+
+&i2c2 {
+         status = "okay";
+
+         ipmb@10 {
+                 compatible = "ipmb-dev";
+                 reg = <0x10>;
+         };
+};
+
+2) Manually from Linux:
+modprobe ipmb-dev-int
+
+
+Instantiate the device
+----------------------
+
+After loading the driver, you can instantiate the device as
+described in 'Documentation/i2c/instantiating-devices'.
+If you have multiple BMCs, each connected to your Satellite MC via
+a different I2C bus, you can instantiate a device for each of
+those BMCs.
+The name of the instantiated device contains the I2C bus number
+associated with it as follows:
+
+BMC1 ------ IPMB/I2C bus 1 ---------|   /dev/ipmb-1
+				Satellite MC
+BMC1 ------ IPMB/I2C bus 2 ---------|   /dev/ipmb-2
+
+For instance, you can instantiate the ipmb-dev-int device from
+user space at the 7 bit address 0x10 on bus 2:
+
+  # echo ipmb-dev 0x1010 > /sys/bus/i2c/devices/i2c-2/new_device
+
+This will create the device file /dev/ipmb-2, which can be accessed
+by the user space program. The device needs to be instantiated
+before running the user space program.

drivers/char/ipmi/Kconfig

···
 	  Provides a driver for the BT (Block Transfer) IPMI interface
 	  found on Aspeed SOCs (AST2400 and AST2500). The driver
 	  implements the BMC side of the BT interface.
+
+config IPMB_DEVICE_INTERFACE
+	tristate 'IPMB Interface handler'
+	depends on I2C_SLAVE
+	help
+	  Provides a driver for a device (Satellite MC) to
+	  receive requests and send responses back to the BMC via
+	  the IPMB interface. This module requires I2C support.

drivers/char/ipmi/Makefile

···
 obj-$(CONFIG_ASPEED_BT_IPMI_BMC) += bt-bmc.o
 obj-$(CONFIG_ASPEED_KCS_IPMI_BMC) += kcs_bmc_aspeed.o
 obj-$(CONFIG_NPCM7XX_KCS_IPMI_BMC) += kcs_bmc_npcm7xx.o
+obj-$(CONFIG_IPMB_DEVICE_INTERFACE) += ipmb_dev_int.o

drivers/char/ipmi/ipmb_dev_int.c

···
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * IPMB driver to receive a request and send a response
+ *
+ * Copyright (C) 2019 Mellanox Techologies, Ltd.
+ *
+ * This was inspired by Brendan Higgins' ipmi-bmc-bt-i2c driver.
+ */
+
+#include <linux/acpi.h>
+#include <linux/errno.h>
+#include <linux/i2c.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/poll.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/wait.h>
+
+#define MAX_MSG_LEN		128
+#define IPMB_REQUEST_LEN_MIN	7
+#define NETFN_RSP_BIT_MASK	0x4
+#define REQUEST_QUEUE_MAX_LEN	256
+
+#define IPMB_MSG_LEN_IDX	0
+#define RQ_SA_8BIT_IDX		1
+#define NETFN_LUN_IDX		2
+
+#define GET_7BIT_ADDR(addr_8bit)	(addr_8bit >> 1)
+#define GET_8BIT_ADDR(addr_7bit)	((addr_7bit << 1) & 0xff)
+
+#define IPMB_MSG_PAYLOAD_LEN_MAX (MAX_MSG_LEN - IPMB_REQUEST_LEN_MIN - 1)
+
+#define SMBUS_MSG_HEADER_LENGTH	2
+#define SMBUS_MSG_IDX_OFFSET	(SMBUS_MSG_HEADER_LENGTH + 1)
+
+struct ipmb_msg {
+	u8 len;
+	u8 rs_sa;
+	u8 netfn_rs_lun;
+	u8 checksum1;
+	u8 rq_sa;
+	u8 rq_seq_rq_lun;
+	u8 cmd;
+	u8 payload[IPMB_MSG_PAYLOAD_LEN_MAX];
+	/* checksum2 is included in payload */
+} __packed;
+
+struct ipmb_request_elem {
+	struct list_head list;
+	struct ipmb_msg request;
+};
+
+struct ipmb_dev {
+	struct i2c_client *client;
+	struct miscdevice miscdev;
+	struct ipmb_msg request;
+	struct list_head request_queue;
+	atomic_t request_queue_len;
+	size_t msg_idx;
+	spinlock_t lock;
+	wait_queue_head_t wait_queue;
+	struct mutex file_mutex;
+};
+
+static inline struct ipmb_dev *to_ipmb_dev(struct file *file)
+{
+	return container_of(file->private_data, struct ipmb_dev, miscdev);
+}
+
+static ssize_t ipmb_read(struct file *file, char __user *buf, size_t count,
+			loff_t *ppos)
+{
+	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
+	struct ipmb_request_elem *queue_elem;
+	struct ipmb_msg msg;
+	ssize_t ret;
+
+	memset(&msg, 0, sizeof(msg));
+
+	spin_lock_irq(&ipmb_dev->lock);
+
+	while (list_empty(&ipmb_dev->request_queue)) {
+		spin_unlock_irq(&ipmb_dev->lock);
+
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+
+		ret = wait_event_interruptible(ipmb_dev->wait_queue,
+				!list_empty(&ipmb_dev->request_queue));
+		if (ret)
+			return ret;
+
+		spin_lock_irq(&ipmb_dev->lock);
+	}
+
+	queue_elem = list_first_entry(&ipmb_dev->request_queue,
+					struct ipmb_request_elem, list);
+	memcpy(&msg, &queue_elem->request, sizeof(msg));
+	list_del(&queue_elem->list);
+	kfree(queue_elem);
+	atomic_dec(&ipmb_dev->request_queue_len);
+
+	spin_unlock_irq(&ipmb_dev->lock);
+
+	count = min_t(size_t, count, msg.len + 1);
+	if (copy_to_user(buf, &msg, count))
+		ret = -EFAULT;
+
+	return ret < 0 ? ret : count;
+}
+
+static ssize_t ipmb_write(struct file *file, const char __user *buf,
+			size_t count, loff_t *ppos)
+{
+	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
+	u8 rq_sa, netf_rq_lun, msg_len;
+	struct i2c_client rq_client;
+	u8 msg[MAX_MSG_LEN];
+	ssize_t ret;
+
+	if (count > sizeof(msg))
+		return -EINVAL;
+
+	if (copy_from_user(&msg, buf, count))
+		return -EFAULT;
+
+	if (count < msg[0])
+		return -EINVAL;
+
+	rq_sa = GET_7BIT_ADDR(msg[RQ_SA_8BIT_IDX]);
+	netf_rq_lun = msg[NETFN_LUN_IDX];
+
+	if (!(netf_rq_lun & NETFN_RSP_BIT_MASK))
+		return -EINVAL;
+
+	/*
+	 * subtract rq_sa and netf_rq_lun from the length of the msg passed to
+	 * i2c_smbus_write_block_data_local
+	 */
+	msg_len = msg[IPMB_MSG_LEN_IDX] - SMBUS_MSG_HEADER_LENGTH;
+
+	strcpy(rq_client.name, "ipmb_requester");
+	rq_client.adapter = ipmb_dev->client->adapter;
+	rq_client.flags = ipmb_dev->client->flags;
+	rq_client.addr = rq_sa;
+
+	ret = i2c_smbus_write_block_data(&rq_client, netf_rq_lun, msg_len,
+					msg + SMBUS_MSG_IDX_OFFSET);
+
+	return ret ? : count;
+}
+
+static unsigned int ipmb_poll(struct file *file, poll_table *wait)
+{
+	struct ipmb_dev *ipmb_dev = to_ipmb_dev(file);
+	unsigned int mask = POLLOUT;
+
+	mutex_lock(&ipmb_dev->file_mutex);
+	poll_wait(file, &ipmb_dev->wait_queue, wait);
+
+	if (atomic_read(&ipmb_dev->request_queue_len))
+		mask |= POLLIN;
+	mutex_unlock(&ipmb_dev->file_mutex);
+
+	return mask;
+}
+
+static const struct file_operations ipmb_fops = {
+	.owner	= THIS_MODULE,
+	.read	= ipmb_read,
+	.write	= ipmb_write,
+	.poll	= ipmb_poll,
+};
+
+/* Called with ipmb_dev->lock held. */
+static void ipmb_handle_request(struct ipmb_dev *ipmb_dev)
+{
+	struct ipmb_request_elem *queue_elem;
+
+	if (atomic_read(&ipmb_dev->request_queue_len) >=
+			REQUEST_QUEUE_MAX_LEN)
+		return;
+
+	queue_elem = kmalloc(sizeof(*queue_elem), GFP_ATOMIC);
+	if (!queue_elem)
+		return;
+
+	memcpy(&queue_elem->request, &ipmb_dev->request,
+		sizeof(struct ipmb_msg));
+	list_add(&queue_elem->list, &ipmb_dev->request_queue);
+	atomic_inc(&ipmb_dev->request_queue_len);
+	wake_up_all(&ipmb_dev->wait_queue);
+}
+
+static u8 ipmb_verify_checksum1(struct ipmb_dev *ipmb_dev, u8 rs_sa)
+{
+	/* The 8 lsb of the sum is 0 when the checksum is valid */
+	return (rs_sa + ipmb_dev->request.netfn_rs_lun +
+		ipmb_dev->request.checksum1);
+}
+
+static bool is_ipmb_request(struct ipmb_dev *ipmb_dev, u8 rs_sa)
+{
+	if (ipmb_dev->msg_idx >= IPMB_REQUEST_LEN_MIN) {
+		if (ipmb_verify_checksum1(ipmb_dev, rs_sa))
+			return false;
+
+		/*
+		 * Check whether this is an IPMB request or
+		 * response.
+		 * The 6 MSB of netfn_rs_lun are dedicated to the netfn
+		 * while the remaining bits are dedicated to the lun.
+		 * If the LSB of the netfn is cleared, it is associated
+		 * with an IPMB request.
+		 * If the LSB of the netfn is set, it is associated with
+		 * an IPMB response.
+		 */
+		if (!(ipmb_dev->request.netfn_rs_lun & NETFN_RSP_BIT_MASK))
+			return true;
+	}
+	return false;
+}
+
+/*
+ * The IPMB protocol only supports I2C Writes so there is no need
+ * to support I2C_SLAVE_READ* events.
+ * This i2c callback function only monitors IPMB request messages
+ * and adds them in a queue, so that they can be handled by
+ * receive_ipmb_request.
+ */
+static int ipmb_slave_cb(struct i2c_client *client,
+			enum i2c_slave_event event, u8 *val)
+{
+	struct ipmb_dev *ipmb_dev = i2c_get_clientdata(client);
+	u8 *buf = (u8 *)&ipmb_dev->request;
+	unsigned long flags;
+
+	spin_lock_irqsave(&ipmb_dev->lock, flags);
+	switch (event) {
+	case I2C_SLAVE_WRITE_REQUESTED:
+		memset(&ipmb_dev->request, 0, sizeof(ipmb_dev->request));
+		ipmb_dev->msg_idx = 0;
+
+		/*
+		 * At index 0, ipmb_msg stores the length of msg,
+		 * skip it for now.
+		 * The len will be populated once the whole
+		 * buf is populated.
+		 *
+		 * The I2C bus driver's responsibility is to pass the
+		 * data bytes to the backend driver; it does not
+		 * forward the i2c slave address.
+		 * Since the first byte in the IPMB message is the
+		 * address of the responder, it is the responsibility
+		 * of the IPMB driver to format the message properly.
+		 * So this driver prepends the address of the responder
+		 * to the received i2c data before the request message
+		 * is handled in userland.
+		 */
+		buf[++ipmb_dev->msg_idx] = GET_8BIT_ADDR(client->addr);
+		break;
+
+	case I2C_SLAVE_WRITE_RECEIVED:
+		if (ipmb_dev->msg_idx >= sizeof(struct ipmb_msg))
+			break;
+
+		buf[++ipmb_dev->msg_idx] = *val;
+		break;
+
+	case I2C_SLAVE_STOP:
+		ipmb_dev->request.len = ipmb_dev->msg_idx;
+
+		if (is_ipmb_request(ipmb_dev, GET_8BIT_ADDR(client->addr)))
+			ipmb_handle_request(ipmb_dev);
+		break;
+
+	default:
+		break;
+	}
+	spin_unlock_irqrestore(&ipmb_dev->lock, flags);
+
+	return 0;
+}
+
+static int ipmb_probe(struct i2c_client *client,
+			const struct i2c_device_id *id)
+{
+	struct ipmb_dev *ipmb_dev;
+	int ret;
+
+	ipmb_dev = devm_kzalloc(&client->dev, sizeof(*ipmb_dev),
+					GFP_KERNEL);
+	if (!ipmb_dev)
+		return -ENOMEM;
+
+	spin_lock_init(&ipmb_dev->lock);
+	init_waitqueue_head(&ipmb_dev->wait_queue);
+	atomic_set(&ipmb_dev->request_queue_len, 0);
+	INIT_LIST_HEAD(&ipmb_dev->request_queue);
+
+	mutex_init(&ipmb_dev->file_mutex);
+
+	ipmb_dev->miscdev.minor = MISC_DYNAMIC_MINOR;
+
+	ipmb_dev->miscdev.name = devm_kasprintf(&client->dev, GFP_KERNEL,
+						"%s%d", "ipmb-",
+						client->adapter->nr);
+	ipmb_dev->miscdev.fops = &ipmb_fops;
+	ipmb_dev->miscdev.parent = &client->dev;
+	ret = misc_register(&ipmb_dev->miscdev);
+	if (ret)
+		return ret;
+
+	ipmb_dev->client = client;
+	i2c_set_clientdata(client, ipmb_dev);
+	ret = i2c_slave_register(client, ipmb_slave_cb);
+	if (ret) {
+		misc_deregister(&ipmb_dev->miscdev);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int ipmb_remove(struct i2c_client *client)
+{
+	struct ipmb_dev *ipmb_dev = i2c_get_clientdata(client);
+
+	i2c_slave_unregister(client);
+	misc_deregister(&ipmb_dev->miscdev);
+
+	return 0;
+}
+
+static const struct i2c_device_id ipmb_id[] = {
+	{ "ipmb-dev", 0 },
+	{},
+};
+MODULE_DEVICE_TABLE(i2c, ipmb_id);
+
+static const struct acpi_device_id acpi_ipmb_id[] = {
+	{ "IPMB0001", 0 },
+	{},
+};
+MODULE_DEVICE_TABLE(acpi, acpi_ipmb_id);
+
+static struct i2c_driver ipmb_driver = {
+	.driver = {
+		.owner = THIS_MODULE,
+		.name = "ipmb-dev",
+		.acpi_match_table = ACPI_PTR(acpi_ipmb_id),
+	},
+	.probe = ipmb_probe,
+	.remove = ipmb_remove,
+	.id_table = ipmb_id,
+};
+module_i2c_driver(ipmb_driver);
+
+MODULE_AUTHOR("Mellanox Technologies");
+MODULE_DESCRIPTION("IPMB driver");
+MODULE_LICENSE("GPL v2");