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Date:   Thu, 23 May 2019 15:03:45 -0700
From:   Eduardo Valentin <eduval@amazon.com>
To:     Haiyue Wang <haiyue.wang@linux.intel.com>
CC:     <wsa@the-dreams.de>, <brendanhiggins@google.com>,
        <linux-i2c@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <openbmc@lists.ozlabs.org>, <jarkko.nikula@linux.intel.com>,
        <andriy.shevchenko@intel.com>, <jae.hyun.yoo@linux.intel.com>
Subject: Re: [PATCH i2c/slave-mqueue v5] i2c: slave-mqueue: add a slave
 backend to receive and queue messages
Message-ID: <20190523220345.GA3417@u40b0340c692b58f6553c.ant.amazon.com>
References: <1524503192-4176-1-git-send-email-haiyue.wang@linux.intel.com>
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Hey Wang,

On Tue, Apr 24, 2018 at 01:06:32AM +0800, Haiyue Wang wrote:
> 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>
> ---
> v4 -> v5:
>  - Typo: bellowing -> the below
> 
> v3 -> v4:
>  - Drop the small message after receiving I2C STOP.
> 
> v2 -> v3:
>  - Just remove the ';' after the end '}' of i2c_slave_mqueue_probe().
> 
> v1 -> v2:
>  - Change MQ_MSGBUF_SIZE and MQ_QUEUE_SIZE to be configurable by Kconfig.
> ---
>  Documentation/i2c/slave-mqueue-backend.rst | 125 ++++++++++++++++++
>  drivers/i2c/Kconfig                        |  25 ++++
>  drivers/i2c/Makefile                       |   1 +
>  drivers/i2c/i2c-slave-mqueue.c             | 203 +++++++++++++++++++++++++++++
>  4 files changed, 354 insertions(+)
>  create mode 100644 Documentation/i2c/slave-mqueue-backend.rst
>  create mode 100644 drivers/i2c/i2c-slave-mqueue.c
> 
> diff --git a/Documentation/i2c/slave-mqueue-backend.rst b/Documentation/i2c/slave-mqueue-backend.rst
> new file mode 100644
> index 0000000..3966cf0
> --- /dev/null
> +++ b/Documentation/i2c/slave-mqueue-backend.rst
> @@ -0,0 +1,125 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=====================================
> +Linux I2C slave message queue backend
> +=====================================
> +
> +:Author: Haiyue Wang <haiyue.wang@linux.intel.com>
> +
> +Some protocols over I2C/SMBus are designed for bi-directional transferring
> +messages by using I2C Master Write protocol. This requires that both sides
> +of the communication have slave addresses.
> +
> +Like 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 I2C slave mqueue (message queue) backend is used to receive and queue
> +messages from the remote i2c intelligent device; and it will add the target
> +slave address (with R/W# bit is always 0) into the message at the first byte,
> +so that userspace can use this byte to dispatch the messages into different
> +handling modules. Also, like IPMB, the address byte is in its message format,
> +it needs it to do checksum.
> +
> +For messages are time related, so this backend will flush the oldest message
> +to queue the newest one.
> +
> +Link
> +----
> +`Intelligent Platform Management Bus
> +Communications Protocol Specification
> +<https://www.intel.com/content/dam/www/public/us/en/documents/product-briefs/ipmp-spec-v1.0.pdf>`_
> +
> +`Management Component Transport Protocol (MCTP)
> +SMBus/I2C Transport Binding Specification
> +<https://www.dmtf.org/sites/default/files/standards/documents/DSP0237_1.1.0.pdf>`_
> +
> +How to use
> +----------
> +For example, the I2C5 bus has slave address 0x10, the below command will create
> +the related message queue interface:
> +
> +    echo slave-mqueue 0x1010 > /sys/bus/i2c/devices/i2c-5/new_device
> +
> +Then you can dump the messages like this:
> +
> +    hexdump -C /sys/bus/i2c/devices/5-1010/slave-mqueue
> +
> +Code Example
> +------------
> +*Note: call 'lseek' before 'read', this is a requirement from kernfs' design.*
> +
> +::
> +
> +  #include <sys/types.h>
> +  #include <sys/stat.h>
> +  #include <unistd.h>
> +  #include <poll.h>
> +  #include <time.h>
> +  #include <fcntl.h>
> +  #include <stdio.h>
> +
> +  int main(int argc, char *argv[])
> +  {
> +          int i, r;
> +          struct pollfd pfd;
> +          struct timespec ts;
> +          unsigned char data[256];
> +
> +          pfd.fd = open(argv[1], O_RDONLY | O_NONBLOCK);
> +          if (pfd.fd < 0)
> +                  return -1;
> +
> +          pfd.events = POLLPRI;
> +
> +          while (1) {
> +                  r = poll(&pfd, 1, 5000);
> +
> +                  if (r < 0)
> +                          break;
> +
> +                  if (r == 0 || !(pfd.revents & POLLPRI))
> +                          continue;
> +
> +                  lseek(pfd.fd, 0, SEEK_SET);
> +                  r = read(pfd.fd, data, sizeof(data));
> +                  if (r <= 0)
> +                          continue;
> +
> +                  clock_gettime(CLOCK_MONOTONIC, &ts);
> +                  printf("[%ld.%.9ld] :", ts.tv_sec, ts.tv_nsec);
> +                  for (i = 0; i < r; i++)
> +                          printf(" %02x", data[i]);
> +                  printf("\n");
> +          }
> +
> +          close(pfd.fd);
> +
> +          return 0;
> +  }
> +
> +Result
> +------
> +*./a.out "/sys/bus/i2c/devices/5-1010/slave-mqueue"*
> +
> +::
> +
> +  [10183.232500449] : 20 18 c8 2c 78 01 5b
> +  [10183.479358348] : 20 18 c8 2c 78 01 5b
> +  [10183.726556812] : 20 18 c8 2c 78 01 5b
> +  [10183.972605863] : 20 18 c8 2c 78 01 5b
> +  [10184.220124772] : 20 18 c8 2c 78 01 5b
> +  [10184.467764166] : 20 18 c8 2c 78 01 5b
> +  [10193.233421784] : 20 18 c8 2c 7c 01 57
> +  [10193.480273460] : 20 18 c8 2c 7c 01 57
> +  [10193.726788733] : 20 18 c8 2c 7c 01 57
> +  [10193.972781945] : 20 18 c8 2c 7c 01 57
> +  [10194.220487360] : 20 18 c8 2c 7c 01 57
> +  [10194.468089259] : 20 18 c8 2c 7c 01 57
> +  [10203.233433099] : 20 18 c8 2c 80 01 53
> +  [10203.481058715] : 20 18 c8 2c 80 01 53
> +  [10203.727610472] : 20 18 c8 2c 80 01 53
> +  [10203.974044856] : 20 18 c8 2c 80 01 53
> +  [10204.220734634] : 20 18 c8 2c 80 01 53
> +  [10204.468461664] : 20 18 c8 2c 80 01 53
> +
> diff --git a/drivers/i2c/Kconfig b/drivers/i2c/Kconfig
> index efc3354..31e57d2 100644
> --- a/drivers/i2c/Kconfig
> +++ b/drivers/i2c/Kconfig
> @@ -118,6 +118,31 @@ if I2C_SLAVE
>  config I2C_SLAVE_EEPROM
>  	tristate "I2C eeprom slave driver"
>  
> +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"
> +	select I2C_SLAVE_MQUEUE_MESSAGE_SIZE
> +	select I2C_SLAVE_MQUEUE_QUEUE_SIZE
> +	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 72c94c6..7ec287b 100644
> --- a/drivers/i2c/Makefile
> +++ b/drivers/i2c/Makefile
> @@ -16,6 +16,7 @@ obj-$(CONFIG_I2C_MUX)		+= i2c-mux.o
>  obj-y				+= algos/ busses/ muxes/
>  obj-$(CONFIG_I2C_STUB)		+= i2c-stub.o
>  obj-$(CONFIG_I2C_SLAVE_EEPROM)	+= i2c-slave-eeprom.o
> +obj-$(CONFIG_I2C_SLAVE_MQUEUE)	+= i2c-slave-mqueue.o
>  
>  ccflags-$(CONFIG_I2C_DEBUG_CORE) := -DDEBUG
>  CFLAGS_i2c-core-base.o := -Wno-deprecated-declarations
> diff --git a/drivers/i2c/i2c-slave-mqueue.c b/drivers/i2c/i2c-slave-mqueue.c
> new file mode 100644
> index 0000000..424f435
> --- /dev/null
> +++ b/drivers/i2c/i2c-slave-mqueue.c
> @@ -0,0 +1,203 @@
> +// 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 */

I wonder why you decided to lock only in/out accesses and not the mq_queue struct.

> +	int			in;
> +	int			out;
> +
> +	struct mq_msg		*curr;
> +	int			truncated; /* drop current if truncated */
> +	struct mq_msg		queue[MQ_QUEUE_SIZE];
> +};
> +
> +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;

Do we need to lock the accesses to msg->buf? how about to msg->len?

> +		} 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);

Is buf a userspace pointer? should it be a copy_to_user() here?

> +		} 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;
> +
> +	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);
> +
> +static struct i2c_driver i2c_slave_mqueue_driver = {
> +	.driver = {
> +		.name	= "i2c-slave-mqueue",
> +	},
> +	.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");
> -- 
> 2.7.4
> 

-- 
All the best,
Eduardo Valentin