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Subject: Re: [PATCH i2c/slave-mqueue v5] i2c: slave-mqueue: add a slave
 backend to receive and queue messages
To:     Eduardo Valentin <eduval@amazon.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
References: <1524503192-4176-1-git-send-email-haiyue.wang@linux.intel.com>
 <20190523220345.GA3417@u40b0340c692b58f6553c.ant.amazon.com>
From:   "Wang, Haiyue" <haiyue.wang@linux.intel.com>
Message-ID: <35a9d066-c732-cb00-04a5-438c948915ae@linux.intel.com>
Date:   Fri, 24 May 2019 10:43:16 +0800
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Thanks for interest, the design idea is from:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/i2c/i2c-slave-eeprom.c?h=v5.2-rc1

and

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/i2c/slave-interface

Then you will get the answer. ;-)

BR,

Haiyue


?? 2019-05-24 06:03, Eduardo Valentin д??:
> 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
>>