Add I2C IPMB support

Some protocols over I2C are designed for bi-directional transferring
messages by using I2C Master Write protocol. Like the MCTP (Management
Component Transport Protocol) and IPMB (Intelligent Platform Management
Bus), they both require that the userspace can receive messages from
I2C dirvers under slave mode.

This new slave mqueue backend is used to receive and queue messages, it
will exposes these messages to userspace by sysfs bin file.

Signed-off-by: Haiyue Wang <haiyue.wang@linux.intel.com>

3 files changed, 241 insertions, 0 deletions

diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
index 438905e2a1d0..339464db1df6 100644
--- a/drivers/i2c/Kconfig
+++ b/drivers/i2c/Kconfig
@@ -133,6 +133,29 @@ config I2C_SLAVE_TESTUNIT
 	  multi-master, SMBus Host Notify, etc. Please read
 	  Documentation/i2c/slave-testunit-backend.rst for further details.
 
+config I2C_SLAVE_MQUEUE_MESSAGE_SIZE
+	int "The message size of I2C mqueue slave"
+	default 120
+
+config I2C_SLAVE_MQUEUE_QUEUE_SIZE
+	int "The queue size of I2C mqueue slave"
+	default 32
+	help
+	  This number MUST be power of 2.
+
+config I2C_SLAVE_MQUEUE
+	tristate "I2C mqueue (message queue) slave driver"
+	help
+	  Some protocols over I2C are designed for bi-directional transferring
+	  messages by using I2C Master Write protocol. This driver is used to
+	  receive and queue messages from the remote I2C device.
+
+	  Userspace can get the messages by reading sysfs file that this driver
+	  exposes.
+
+	  This support is also available as a module. If so, the module will be
+	  called i2c-slave-mqueue.
+
 endif
 
 config I2C_DEBUG_CORE
diff --git a/drivers/i2c/Makefile b/drivers/i2c/Makefile
index c1d493dc9bac..0442e5cf8587 100644
--- a/drivers/i2c/Makefile
+++ b/drivers/i2c/Makefile
@@ -17,5 +17,6 @@ obj-y				+= algos/ busses/ muxes/
 obj-$(CONFIG_I2C_STUB)		+= i2c-stub.o
 obj-$(CONFIG_I2C_SLAVE_EEPROM)	+= i2c-slave-eeprom.o
 obj-$(CONFIG_I2C_SLAVE_TESTUNIT)	+= i2c-slave-testunit.o
+obj-$(CONFIG_I2C_SLAVE_MQUEUE)	+= i2c-slave-mqueue.o
 
 ccflags-$(CONFIG_I2C_DEBUG_CORE) := -DDEBUG
diff --git a/drivers/i2c/i2c-slave-mqueue.c b/drivers/i2c/i2c-slave-mqueue.c
new file mode 100644
index 000000000000..6014bca0ff2a
--- /dev/null
+++ b/drivers/i2c/i2c-slave-mqueue.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2017 - 2018, Intel Corporation.
+
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/sysfs.h>
+
+#define MQ_MSGBUF_SIZE		CONFIG_I2C_SLAVE_MQUEUE_MESSAGE_SIZE
+#define MQ_QUEUE_SIZE		CONFIG_I2C_SLAVE_MQUEUE_QUEUE_SIZE
+#define MQ_QUEUE_NEXT(x)	(((x) + 1) & (MQ_QUEUE_SIZE - 1))
+
+struct mq_msg {
+	int	len;
+	u8	*buf;
+};
+
+struct mq_queue {
+	struct bin_attribute	bin;
+	struct kernfs_node	*kn;
+
+	spinlock_t		lock; /* spinlock for queue index handling */
+	int			in;
+	int			out;
+
+	struct mq_msg		*curr;
+	int			truncated; /* drop current if truncated */
+	struct mq_msg		*queue;
+};
+
+static int i2c_slave_mqueue_callback(struct i2c_client *client,
+				     enum i2c_slave_event event, u8 *val)
+{
+	struct mq_queue *mq = i2c_get_clientdata(client);
+	struct mq_msg *msg = mq->curr;
+	int ret = 0;
+
+	switch (event) {
+	case I2C_SLAVE_WRITE_REQUESTED:
+		mq->truncated = 0;
+
+		msg->len = 1;
+		msg->buf[0] = client->addr << 1;
+		break;
+
+	case I2C_SLAVE_WRITE_RECEIVED:
+		if (msg->len < MQ_MSGBUF_SIZE) {
+			msg->buf[msg->len++] = *val;
+		} else {
+			dev_err(&client->dev, "message is truncated!\n");
+			mq->truncated = 1;
+			ret = -EINVAL;
+		}
+		break;
+
+	case I2C_SLAVE_STOP:
+		if (unlikely(mq->truncated || msg->len < 2))
+			break;
+
+		spin_lock(&mq->lock);
+		mq->in = MQ_QUEUE_NEXT(mq->in);
+		mq->curr = &mq->queue[mq->in];
+		mq->curr->len = 0;
+
+		/* Flush the oldest message */
+		if (mq->out == mq->in)
+			mq->out = MQ_QUEUE_NEXT(mq->out);
+		spin_unlock(&mq->lock);
+
+		kernfs_notify(mq->kn);
+		break;
+
+	default:
+		*val = 0xFF;
+		break;
+	}
+
+	return ret;
+}
+
+static ssize_t i2c_slave_mqueue_bin_read(struct file *filp,
+					 struct kobject *kobj,
+					 struct bin_attribute *attr,
+					 char *buf, loff_t pos, size_t count)
+{
+	struct mq_queue *mq;
+	struct mq_msg *msg;
+	unsigned long flags;
+	bool more = false;
+	ssize_t ret = 0;
+
+	mq = dev_get_drvdata(container_of(kobj, struct device, kobj));
+
+	spin_lock_irqsave(&mq->lock, flags);
+	if (mq->out != mq->in) {
+		msg = &mq->queue[mq->out];
+
+		if (msg->len <= count) {
+			ret = msg->len;
+			memcpy(buf, msg->buf, ret);
+		} else {
+			ret = -EOVERFLOW; /* Drop this HUGE one. */
+		}
+
+		mq->out = MQ_QUEUE_NEXT(mq->out);
+		if (mq->out != mq->in)
+			more = true;
+	}
+	spin_unlock_irqrestore(&mq->lock, flags);
+
+	if (more)
+		kernfs_notify(mq->kn);
+
+	return ret;
+}
+
+static int i2c_slave_mqueue_probe(struct i2c_client *client,
+				  const struct i2c_device_id *id)
+{
+	struct device *dev = &client->dev;
+	struct mq_queue *mq;
+	int ret, i;
+	void *buf;
+
+	mq = devm_kzalloc(dev, sizeof(*mq), GFP_KERNEL);
+	if (!mq)
+		return -ENOMEM;
+
+	BUILD_BUG_ON(!is_power_of_2(MQ_QUEUE_SIZE));
+
+	buf = devm_kmalloc_array(dev, MQ_QUEUE_SIZE, MQ_MSGBUF_SIZE,
+				 GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	mq->queue = devm_kzalloc(dev, sizeof(*mq->queue) * MQ_QUEUE_SIZE,
+				 GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	for (i = 0; i < MQ_QUEUE_SIZE; i++)
+		mq->queue[i].buf = buf + i * MQ_MSGBUF_SIZE;
+
+	i2c_set_clientdata(client, mq);
+
+	spin_lock_init(&mq->lock);
+	mq->curr = &mq->queue[0];
+
+	sysfs_bin_attr_init(&mq->bin);
+	mq->bin.attr.name = "slave-mqueue";
+	mq->bin.attr.mode = 0400;
+	mq->bin.read = i2c_slave_mqueue_bin_read;
+	mq->bin.size = MQ_MSGBUF_SIZE * MQ_QUEUE_SIZE;
+
+	ret = sysfs_create_bin_file(&dev->kobj, &mq->bin);
+	if (ret)
+		return ret;
+
+	mq->kn = kernfs_find_and_get(dev->kobj.sd, mq->bin.attr.name);
+	if (!mq->kn) {
+		sysfs_remove_bin_file(&dev->kobj, &mq->bin);
+		return -EFAULT;
+	}
+
+	ret = i2c_slave_register(client, i2c_slave_mqueue_callback);
+	if (ret) {
+		kernfs_put(mq->kn);
+		sysfs_remove_bin_file(&dev->kobj, &mq->bin);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int i2c_slave_mqueue_remove(struct i2c_client *client)
+{
+	struct mq_queue *mq = i2c_get_clientdata(client);
+
+	i2c_slave_unregister(client);
+
+	kernfs_put(mq->kn);
+	sysfs_remove_bin_file(&client->dev.kobj, &mq->bin);
+
+	return 0;
+}
+
+static const struct i2c_device_id i2c_slave_mqueue_id[] = {
+	{ "slave-mqueue", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, i2c_slave_mqueue_id);
+
+#if IS_ENABLED(CONFIG_OF)
+static const struct of_device_id i2c_slave_mqueue_of_match[] = {
+	{ .compatible = "slave-mqueue", .data = (void *)0 },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, i2c_slave_mqueue_of_match);
+#endif
+
+static struct i2c_driver i2c_slave_mqueue_driver = {
+	.driver = {
+		.name	= "i2c-slave-mqueue",
+		.of_match_table = of_match_ptr(i2c_slave_mqueue_of_match),
+	},
+	.probe		= i2c_slave_mqueue_probe,
+	.remove		= i2c_slave_mqueue_remove,
+	.id_table	= i2c_slave_mqueue_id,
+};
+module_i2c_driver(i2c_slave_mqueue_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Haiyue Wang <haiyue.wang@linux.intel.com>");
+MODULE_DESCRIPTION("I2C slave mode for receiving and queuing messages");