Message-ID: <4e2b25da-3a19-ea8d-8152-2ef10637f476@linux.intel.com>
Date:   Tue, 20 Mar 2018 09:44:14 +0800
From:   "Wang, Haiyue" <haiyue.wang@...ux.intel.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        wsa@...-dreams.de, brendanhiggins@...gle.com,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     jarkko.nikula@...ux.intel.com, jae.hyun.yoo@...ux.intel.com
Subject: Re: [PATCH i2c/slave-mqueue v1] i2c: slave-mqueue: add a slave
 backend to receive and queue messages

Thanks, Andy.


Hi Wolfram,

Let me introduce some development background, it is used for OpenBMC 
project,

which belongs to the Linux Foundation now 
(https://www.linuxfoundation.org/blog/openbmc-project-community-comes-together-at-the-linux-foundation-to-define-open-source-implementation-of-bmc-firmware-stack/).

1. *https://goo.gl/WgvPFi*

*** 
<https://goo.gl/WgvPFi>***https://lists.ozlabs.org/pipermail/openbmc/2018-January/010493.html* 
<https://goo.gl/WgvPFi>*

**

*IPMI is embedded within IPMB (similar to KCS, BT?)*

*

  *

    Who started, who responded to messages

  *

    We need a kernel interface for handling a multi-master slave

  *

    Dell has a non-standard i2c IPMB interface

      o

        Kernel maintains table of outstanding commands

  *

    Brendan suggests we need a kernel driver for doing both MCTP and IPMB

  *

    We can’t do them both in usersland as MCTP makes extensions to SMBUS
    in order to allow arbitration. Problematic extension is the “MCTP
    fairness arbitration”. Requires the i2c controllers on the bus
    (masters/slaves) to observe the line for a certain period of time in
    order to see who is using the line. There’s no userspace API for
    this, and it the timing requirements are tight

  *

    Slave mode is not yet exposed to the user

  *

    As we don’t have a userspace interface, it makes sense to add a new one

*

BR,
Haiyue

On 2018-03-20 03:32, Andy Shevchenko wrote:
> On Sat, 2018-03-17 at 11:48 +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.
>>
> Wolfram, I'm not sure this is the best approach, though I can't propose
> anything else right now.
>
> If you are satisfied with it, I give a formal
>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
>
>> Signed-off-by: Haiyue Wang <haiyue.wang@...ux.intel.com>
>> ---
>>   Documentation/i2c/slave-mqueue-backend.rst | 125 ++++++++++++++++++
>>   drivers/i2c/Kconfig                        |  13 ++
>>   drivers/i2c/Makefile                       |   1 +
>>   drivers/i2c/i2c-slave-mqueue.c             | 202
>> +++++++++++++++++++++++++++++
>>   4 files changed, 341 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..69d6437
>> --- /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@...ux.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, bellowing 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..7053b5b 100644
>> --- a/drivers/i2c/Kconfig
>> +++ b/drivers/i2c/Kconfig
>> @@ -118,6 +118,19 @@ if I2C_SLAVE
>>   config I2C_SLAVE_EEPROM
>>   	tristate "I2C eeprom slave driver"
>>   
>> +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 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..a486e85
>> --- /dev/null
>> +++ b/drivers/i2c/i2c-slave-mqueue.c
>> @@ -0,0 +1,202 @@
>> +// 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		128
>> +#define MQ_QUEUE_SIZE		32
>> +#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[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;
>> +		} else {
>> +			dev_err(&client->dev, "message is
>> truncated!\n");
>> +			mq->truncated = 1;
>> +			ret = -EINVAL;
>> +		}
>> +		break;
>> +
>> +	case I2C_SLAVE_STOP:
>> +		if (unlikely(mq->truncated))
>> +			break;
>> +
>> +		spin_lock(&mq->lock);
>> +		mq->in = MQ_QUEUE_NEXT(mq->in);
>> +		mq->curr = &mq->queue[mq->in];
>> +
>> +		/* 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;
>> +
>> +	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@...ux.intel.com>");
>> +MODULE_DESCRIPTION("I2C slave mode for receiving and queuing
>> messages");

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