[v6,1/4] ipmi: ssif_bmc: Add SSIF BMC driver

Commit Message

Quan Nguyen March 10, 2022, 11:41 a.m. UTC

The SMBus system interface (SSIF) IPMI BMC driver can be used to perform
in-band IPMI communication with their host in management (BMC) side.

Signed-off-by: Quan Nguyen <[e-mail]>
---
v6:
  + Drop the use of slave_enable()                             [Wolfram]
  + Make i2c-aspeed to issue RxCmdLast command on all
  I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy   [Quan]
  + Make i2c slave to return -EBUSY when it's busy                [Quan]
  + Drop the aborting feature as return Completion Code 0xFF may stop
  host to retry and make ipmi_ssif.so fails to load               [Quan]
  + Add timer to recover slave from busy state when no response   [Quan]
  + Clean request/response buffer appropriately                   [Quan]
  + Add some minor change on error and warning messages           [Quan]

v5:
  + None

v4:
  + Send response with Completion code 0xFF when aborting         [Quan]
  + Added bounding check on SMBus writes and the whole request     [Dan]
  + Moved buffer to end of struct ssif_bmc_ctx to avoid context
    corruption if somehow buffer is written past the end           [Dan]
  + Return -EINVAL if userspace buffer too small, dont
    silence truncate                                       [Corey, Joel]
  + Not necessary to check NONBLOCK in lock                      [Corey]
  + Enforce one user at a time                                    [Joel]
  + Reject write with invalid response length from userspace     [Corey]
  + Add state machines for better ssif bmc state handling         [Quan]
  + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
    SSIF BMC driver                                               [Quan]
  + Change compatible string "aspeed,ast2500-ssif-bmc" to
    "ampere,ssif-bmc"                                             [Quan]
  + Abort current request with invalid SMBus write or
    invalid command                                               [Quan]
  + Abort all request if there is pending response                [Quan]
  + Changed validate_pec() to validate_request()                  [Quan]
  + Add unsupported_smbus_cmd() to handle unknown SMBus command   [Quan]
  + Print internal state string for ease investigating issue      [Quan]
  + Move to READY state on SLAVE_STOP event                       [Quan]
  + Change initilize_transfer() to process_smbus_cmd()            [Quan]
  + Introduce functions for each slave event                      [Quan]

v3:
  + Removed redundant license info                                [Joel]
  + Switched to use traditional if-else                           [Joel]
  + Removed unused ssif_bmc_ioctl()                               [Joel]
  + Made handle_request()/complete_response() to return void      [Joel]
  + Refactored send_ssif_bmc_response() and
  receive_ssif_bmc_request()                                     [Corey]
  + Removed mutex                                                [Corey]
  + Use spin_lock/unlock_irqsave/restore in callback             [Corey]
  + Removed the unnecessary memset                               [Corey]
  + Switch to use dev_err()                                      [Corey]

v2:
  + Fixed compiling error with COMPILE_TEST for arc

 drivers/char/ipmi/Kconfig    |  11 +
 drivers/char/ipmi/Makefile   |   1 +
 drivers/char/ipmi/ssif_bmc.c | 791 +++++++++++++++++++++++++++++++++++
 drivers/char/ipmi/ssif_bmc.h | 102 +++++
 4 files changed, 905 insertions(+)
 create mode 100644 drivers/char/ipmi/ssif_bmc.c
 create mode 100644 drivers/char/ipmi/ssif_bmc.h

Comments

Corey Minyard March 11, 2022, 1:19 a.m. UTC | #1

On Thu, Mar 10, 2022 at 06:41:16PM +0700, Quan Nguyen wrote:
> The SMBus system interface (SSIF) IPMI BMC driver can be used to perform
> in-band IPMI communication with their host in management (BMC) side.

Thanks for the update, and removing slave_enable().

I spent some quality time with this, and it looks like there are places
where you don't check lengths before indexing arrays.  I've marked
several of these, but you need to check it all through this.

I have a few other comments, too.

-corey

> 
> Signed-off-by: Quan Nguyen <[e-mail]>
> ---
> v6:
>   + Drop the use of slave_enable()                             [Wolfram]
>   + Make i2c-aspeed to issue RxCmdLast command on all
>   I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy   [Quan]
>   + Make i2c slave to return -EBUSY when it's busy                [Quan]
>   + Drop the aborting feature as return Completion Code 0xFF may stop
>   host to retry and make ipmi_ssif.so fails to load               [Quan]
>   + Add timer to recover slave from busy state when no response   [Quan]
>   + Clean request/response buffer appropriately                   [Quan]
>   + Add some minor change on error and warning messages           [Quan]
> 
> v5:
>   + None
> 
> v4:
>   + Send response with Completion code 0xFF when aborting         [Quan]
>   + Added bounding check on SMBus writes and the whole request     [Dan]
>   + Moved buffer to end of struct ssif_bmc_ctx to avoid context
>     corruption if somehow buffer is written past the end           [Dan]
>   + Return -EINVAL if userspace buffer too small, dont
>     silence truncate                                       [Corey, Joel]
>   + Not necessary to check NONBLOCK in lock                      [Corey]
>   + Enforce one user at a time                                    [Joel]
>   + Reject write with invalid response length from userspace     [Corey]
>   + Add state machines for better ssif bmc state handling         [Quan]
>   + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
>     SSIF BMC driver                                               [Quan]
>   + Change compatible string "aspeed,ast2500-ssif-bmc" to
>     "ampere,ssif-bmc"                                             [Quan]
>   + Abort current request with invalid SMBus write or
>     invalid command                                               [Quan]
>   + Abort all request if there is pending response                [Quan]
>   + Changed validate_pec() to validate_request()                  [Quan]
>   + Add unsupported_smbus_cmd() to handle unknown SMBus command   [Quan]
>   + Print internal state string for ease investigating issue      [Quan]
>   + Move to READY state on SLAVE_STOP event                       [Quan]
>   + Change initilize_transfer() to process_smbus_cmd()            [Quan]
>   + Introduce functions for each slave event                      [Quan]
> 
> v3:
>   + Removed redundant license info                                [Joel]
>   + Switched to use traditional if-else                           [Joel]
>   + Removed unused ssif_bmc_ioctl()                               [Joel]
>   + Made handle_request()/complete_response() to return void      [Joel]
>   + Refactored send_ssif_bmc_response() and
>   receive_ssif_bmc_request()                                     [Corey]
>   + Removed mutex                                                [Corey]
>   + Use spin_lock/unlock_irqsave/restore in callback             [Corey]
>   + Removed the unnecessary memset                               [Corey]
>   + Switch to use dev_err()                                      [Corey]
> 
> v2:
>   + Fixed compiling error with COMPILE_TEST for arc
> 
>  drivers/char/ipmi/Kconfig    |  11 +
>  drivers/char/ipmi/Makefile   |   1 +
>  drivers/char/ipmi/ssif_bmc.c | 791 +++++++++++++++++++++++++++++++++++
>  drivers/char/ipmi/ssif_bmc.h | 102 +++++
>  4 files changed, 905 insertions(+)
>  create mode 100644 drivers/char/ipmi/ssif_bmc.c
>  create mode 100644 drivers/char/ipmi/ssif_bmc.h
> 
> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
> index b061e6b513ed..18a89093d64e 100644
> --- a/drivers/char/ipmi/Kconfig
> +++ b/drivers/char/ipmi/Kconfig
> @@ -169,6 +169,17 @@ config ASPEED_BT_IPMI_BMC
>  	  found on Aspeed SOCs (AST2400 and AST2500). The driver
>  	  implements the BMC side of the BT interface.
>  
> +config SSIF_IPMI_BMC
> +	tristate "SSIF IPMI BMC driver"
> +	select I2C
> +	select I2C_SLAVE
> +	help
> +	  This enables the IPMI SMBus system interface (SSIF) at the
> +	  management (BMC) side.
> +
> +	  The driver implements the BMC side of the SMBus system
> +	  interface (SSIF).
> +
>  config IPMB_DEVICE_INTERFACE
>  	tristate 'IPMB Interface handler'
>  	depends on I2C
> diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
> index 7ce790efad92..cb6138b8ded9 100644
> --- a/drivers/char/ipmi/Makefile
> +++ b/drivers/char/ipmi/Makefile
> @@ -30,3 +30,4 @@ 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
> +obj-$(CONFIG_SSIF_IPMI_BMC) += ssif_bmc.o
> diff --git a/drivers/char/ipmi/ssif_bmc.c b/drivers/char/ipmi/ssif_bmc.c
> new file mode 100644
> index 000000000000..62db97773654
> --- /dev/null
> +++ b/drivers/char/ipmi/ssif_bmc.c
> @@ -0,0 +1,791 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * The driver for BMC side of SSIF interface
> + *
> + * Copyright (c) 2022, Ampere Computing LLC
> + *
> + */
> +
> +#include <linux/i2c.h>
> +#include <linux/miscdevice.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/poll.h>
> +#include <linux/sched.h>
> +#include <linux/mutex.h>
> +#include <linux/spinlock.h>
> +#include <linux/timer.h>
> +#include <linux/jiffies.h>
> +
> +#include "ssif_bmc.h"
> +
> +static const char *state_to_string(enum ssif_state state)
> +{
> +	switch (state) {
> +	case SSIF_READY:
> +		return "SSIF_READY";
> +	case SSIF_START:
> +		return "SSIF_START";
> +	case SSIF_SMBUS_CMD:
> +		return "SSIF_SMBUS_CMD";
> +	case SSIF_REQ_RECVING:
> +		return "SSIF_REQ_RECVING";
> +	case SSIF_RES_SENDING:
> +		return "SSIF_RES_SENDING";
> +	case SSIF_BAD_SMBUS:
> +		return "SSIF_BAD_SMBUS";
> +	default:
> +		return "SSIF_STATE_UNKNOWN";
> +	}
> +}
> +
> +/* Handle SSIF message that will be sent to user */
> +static ssize_t ssif_bmc_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	struct ssif_msg msg;
> +	unsigned long flags;
> +	ssize_t ret;
> +
> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	while (!ssif_bmc->request_available) {
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +		if (file->f_flags & O_NONBLOCK)
> +			return -EAGAIN;
> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
> +					       ssif_bmc->request_available);
> +		if (ret)
> +			return ret;
> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	}
> +
> +	if (count < min_t(ssize_t, ssif_msg_len(&ssif_bmc->request), sizeof(struct ssif_msg))) {
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +		ret = -EINVAL;
> +	} else {
> +		count = min_t(ssize_t, ssif_msg_len(&ssif_bmc->request), sizeof(struct ssif_msg));
> +		memcpy(&msg, &ssif_bmc->request, count);
> +		ssif_bmc->request_available = false;
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +
> +		ret = copy_to_user(buf, &msg, count);
> +	}
> +
> +	return (ret < 0) ? ret : count;
> +}
> +
> +/* Handle SSIF message that is written by user */
> +static ssize_t ssif_bmc_write(struct file *file, const char __user *buf, size_t count,
> +			      loff_t *ppos)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	struct ssif_msg msg;
> +	unsigned long flags;
> +	ssize_t ret;
> +
> +	if (count > sizeof(struct ssif_msg))
> +		return -EINVAL;
> +
> +	ret = copy_from_user(&msg, buf, count);
> +	if (ret)
> +		return ret;
> +
> +	if (!msg.len || count < ssif_msg_len(&msg))
> +		return -EINVAL;
> +
> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	while (ssif_bmc->response_in_progress) {
> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +		if (file->f_flags & O_NONBLOCK)
> +			return -EAGAIN;
> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
> +					       !ssif_bmc->response_in_progress);
> +		if (ret)
> +			return ret;
> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
> +	}
> +
> +	memcpy(&ssif_bmc->response, &msg, count);
> +	ssif_bmc->is_singlepart_read = (ssif_msg_len(&msg) <= MAX_PAYLOAD_PER_TRANSACTION + 1);
> +
> +	ssif_bmc->response_in_progress = true;
> +
> +	/* ssif_bmc not busy */
> +	ssif_bmc->busy = false;
> +
> +	if (ssif_bmc->response_timer_inited) {
> +		del_timer(&ssif_bmc->response_timer);
> +		ssif_bmc->response_timer_inited = false;
> +	}
> +	/* Clean old request buffer */
> +	memset(&ssif_bmc->request, 0, sizeof(struct ssif_msg));
> +
> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +
> +	return count;
> +}
> +
> +static int ssif_bmc_open(struct inode *inode, struct file *file)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	int ret = 0;
> +
> +	spin_lock_irq(&ssif_bmc->lock);
> +	if (!ssif_bmc->running)
> +		ssif_bmc->running = 1;
> +	else
> +		ret = -EBUSY;
> +	spin_unlock_irq(&ssif_bmc->lock);
> +
> +	return ret;
> +}
> +
> +static unsigned int ssif_bmc_poll(struct file *file, poll_table *wait)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +	unsigned int mask = 0;
> +
> +	poll_wait(file, &ssif_bmc->wait_queue, wait);
> +
> +	spin_lock_irq(&ssif_bmc->lock);
> +	/* The request is available, userspace application can get the request */
> +	if (ssif_bmc->request_available)
> +		mask |= POLLIN;
> +
> +	spin_unlock_irq(&ssif_bmc->lock);
> +
> +	return mask;
> +}
> +
> +static int ssif_bmc_release(struct inode *inode, struct file *file)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
> +
> +	spin_lock_irq(&ssif_bmc->lock);
> +	ssif_bmc->running = 0;
> +	spin_unlock_irq(&ssif_bmc->lock);
> +
> +	return 0;
> +}
> +
> +/*
> + * System calls to device interface for user apps
> + */
> +static const struct file_operations ssif_bmc_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= ssif_bmc_open,
> +	.read		= ssif_bmc_read,
> +	.write		= ssif_bmc_write,
> +	.release	= ssif_bmc_release,
> +	.poll		= ssif_bmc_poll,
> +};
> +
> +/* Called with ssif_bmc->lock held. */
> +static void complete_response(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	/* Invalidate response in buffer to denote it having been sent. */
> +	ssif_bmc->response.len = 0;
> +	ssif_bmc->response_in_progress = false;
> +	ssif_bmc->nbytes_processed = 0;
> +	ssif_bmc->remain_len = 0;
> +	ssif_bmc->busy = false;
> +	memset(&ssif_bmc->response_buf, 0, MAX_PAYLOAD_PER_TRANSACTION);
> +	wake_up_all(&ssif_bmc->wait_queue);
> +}
> +
> +static void response_timeout(struct timer_list *t)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, response_timer);
> +	unsigned long flags;
> +

Is there a possible race here?  The timeout can happen at the same time
as a received message, will something bad happen if that's the case?

> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +
> +	/* Recover ssif_bmc from busy */
> +	ssif_bmc->busy = false;
> +	del_timer(&ssif_bmc->response_timer);

You don't need to delete the timer, it's in the timeout.

> +	ssif_bmc->response_timer_inited = false;
> +
> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +}
> +
> +/* Called with ssif_bmc->lock held. */
> +static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	/* set ssif_bmc to busy waiting for response */
> +	ssif_bmc->busy = true;
> +
> +	/* Request message is available to process */
> +	ssif_bmc->request_available = true;
> +
> +	/* Clean old response buffer */
> +	memset(&ssif_bmc->response, 0, sizeof(struct ssif_msg));
> +
> +	/* This is the new READ request.*/
> +	wake_up_all(&ssif_bmc->wait_queue);
> +
> +	/* Armed timer to recover slave from busy state in case of no response */
> +	if (!ssif_bmc->response_timer_inited) {
> +		timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
> +		ssif_bmc->response_timer_inited = true;
> +	}
> +	mod_timer(&ssif_bmc->response_timer, jiffies + msecs_to_jiffies(RESPONSE_TIMEOUT));
> +}
> +
> +static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	u8 response_len = 0;
> +	int idx = 0;
> +	u8 data_len;
> +
> +	data_len = ssif_bmc->response.len;
> +	switch (ssif_bmc->smbus_cmd) {
> +	case SSIF_IPMI_MULTIPART_READ_START:
> +		/*
> +		 * Read Start length is 32 bytes.
> +		 * Read Start transfer first 30 bytes of IPMI response
> +		 * and 2 special code 0x00, 0x01.
> +		 */
> +		*val = MAX_PAYLOAD_PER_TRANSACTION;
> +		ssif_bmc->remain_len = data_len - MAX_IPMI_DATA_PER_START_TRANSACTION;
> +		ssif_bmc->block_num = 0;

Do you need to validate the data length before using this?
This applies for lots of places through here.

> +
> +		ssif_bmc->response_buf[idx++] = 0x00; /* Start Flag */
> +		ssif_bmc->response_buf[idx++] = 0x01; /* Start Flag */
> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.netfn_lun;
> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.cmd;
> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.payload[0];
> +
> +		response_len = MAX_PAYLOAD_PER_TRANSACTION - idx;
> +
> +		memcpy(&ssif_bmc->response_buf[idx], &ssif_bmc->response.payload[1],
> +		       response_len);
> +		break;
> +
> +	case SSIF_IPMI_MULTIPART_READ_MIDDLE:
> +		/*
> +		 * IPMI READ Middle or READ End messages can carry up to 31 bytes
> +		 * IPMI data plus block number byte.
> +		 */
> +		if (ssif_bmc->remain_len < MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
> +			/*
> +			 * This is READ End message
> +			 *  Return length is the remaining response data length
> +			 *  plus block number
> +			 *  Block number 0xFF is to indicate this is last message
> +			 *
> +			 */
> +			*val = ssif_bmc->remain_len + 1;
> +			ssif_bmc->block_num = 0xFF;
> +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
> +			response_len = ssif_bmc->remain_len;
> +			/* Clean the buffer */
> +			memset(&ssif_bmc->response_buf[idx], 0, MAX_PAYLOAD_PER_TRANSACTION - idx);
> +		} else {
> +			/*
> +			 * This is READ Middle message
> +			 *  Response length is the maximum SMBUS transfer length
> +			 *  Block number byte is incremented
> +			 * Return length is maximum SMBUS transfer length
> +			 */
> +			*val = MAX_PAYLOAD_PER_TRANSACTION;
> +			ssif_bmc->remain_len -= MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
> +			response_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
> +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
> +			ssif_bmc->block_num++;
> +		}
> +
> +		memcpy(&ssif_bmc->response_buf[idx],
> +		       ssif_bmc->response.payload + 1 + ssif_bmc->nbytes_processed,
> +		       response_len);
> +		break;
> +
> +	default:
> +		/* Do not expect to go to this case */
> +		dev_err(&ssif_bmc->client->dev,
> +			"%s: Unexpected SMBus command 0x%x\n",
> +			__func__, ssif_bmc->smbus_cmd);
> +		break;
> +	}
> +
> +	ssif_bmc->nbytes_processed += response_len;
> +}
> +
> +/* Process the IPMI response that will be read by master */
> +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	u8 *buf;
> +	u8 pec_len, addr, len;
> +	u8 pec = 0;
> +
> +	pec_len = ssif_bmc->pec_support ? 1 : 0;
> +	/* PEC - Start Read Address */
> +	addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
> +	pec = i2c_smbus_pec(pec, &addr, 1);
> +	/* PEC - SSIF Command */
> +	pec = i2c_smbus_pec(pec, &ssif_bmc->smbus_cmd, 1);
> +	/* PEC - Restart Write Address */
> +	addr = addr | 0x01;
> +	pec = i2c_smbus_pec(pec, &addr, 1);
> +
> +	if (ssif_bmc->is_singlepart_read) {
> +		/* Single-part Read processing */
> +		buf = (u8 *)&ssif_bmc->response;
> +
> +		if (ssif_bmc->response.len && ssif_bmc->msg_idx < ssif_bmc->response.len) {
> +			ssif_bmc->msg_idx++;
> +			*val = buf[ssif_bmc->msg_idx];
> +		} else if (ssif_bmc->response.len && ssif_bmc->msg_idx == ssif_bmc->response.len) {
> +			ssif_bmc->msg_idx++;
> +			*val = i2c_smbus_pec(pec, buf, ssif_msg_len(&ssif_bmc->response));
> +		} else {

I thought for a second that this was wrong, but I think it's correct.
Supply zero if you don't have data.

> +			*val = 0;
> +		}
> +		/* Invalidate response buffer to denote it is sent */
> +		if (ssif_bmc->msg_idx + 1 >= (ssif_msg_len(&ssif_bmc->response) + pec_len))
> +			complete_response(ssif_bmc);
> +	} else {
> +		/* Multi-part Read processing */

You don't check the length here like you did above.  I think that's
required.

> +		switch (ssif_bmc->smbus_cmd) {
> +		case SSIF_IPMI_MULTIPART_READ_START:
> +		case SSIF_IPMI_MULTIPART_READ_MIDDLE:
> +			buf = (u8 *)&ssif_bmc->response_buf;
> +			*val = buf[ssif_bmc->msg_idx];
> +			ssif_bmc->msg_idx++;
> +			break;
> +		default:
> +			/* Do not expect to go to this case */
> +			dev_err(&ssif_bmc->client->dev,
> +				"%s: Unexpected SMBus command 0x%x\n",
> +				__func__, ssif_bmc->smbus_cmd);
> +			break;
> +		}
> +
> +		len = (ssif_bmc->block_num == 0xFF) ?
> +		       ssif_bmc->remain_len + 1 : MAX_PAYLOAD_PER_TRANSACTION;
> +		if (ssif_bmc->msg_idx == (len + 1)) {
> +			pec = i2c_smbus_pec(pec, &len, 1);
> +			*val = i2c_smbus_pec(pec, ssif_bmc->response_buf, len);
> +		}
> +		/* Invalidate response buffer to denote last response is sent */
> +		if (ssif_bmc->block_num == 0xFF &&
> +		    ssif_bmc->msg_idx > (ssif_bmc->remain_len + pec_len)) {
> +			complete_response(ssif_bmc);
> +		}
> +	}
> +}
> +
> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	u8 *buf = (u8 *)&ssif_bmc->request;
> +
> +	if (ssif_bmc->msg_idx >= sizeof(struct ssif_msg))
> +		return;
> +
> +	switch (ssif_bmc->smbus_cmd) {
> +	case SSIF_IPMI_SINGLEPART_WRITE:
> +		buf[ssif_bmc->msg_idx - 1] = *val;
> +		ssif_bmc->msg_idx++;
> +
> +		break;
> +	case SSIF_IPMI_MULTIPART_WRITE_START:
> +		if (ssif_bmc->msg_idx == 1)
> +			ssif_bmc->request.len = 0;
> +
> +		fallthrough;
> +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
> +		/* The len should always be 32 */
> +		if (ssif_bmc->msg_idx == 1 && *val != MAX_PAYLOAD_PER_TRANSACTION)
> +			dev_warn(&ssif_bmc->client->dev,
> +				 "Warn: Invalid Multipart Write len");
> +
> +		fallthrough;
> +	case SSIF_IPMI_MULTIPART_WRITE_END:
> +		/* Multi-part write, 2nd byte received is length */
> +		if (ssif_bmc->msg_idx == 1) {
> +			if (*val > MAX_PAYLOAD_PER_TRANSACTION)
> +				dev_warn(&ssif_bmc->client->dev,
> +					 "Warn: Invalid Multipart Write End len");
> +
> +			ssif_bmc->request.len += *val;
> +			ssif_bmc->recv_len = *val;
> +
> +			/* request len should never exceeded 255 bytes */
> +			if (ssif_bmc->request.len > 255)
> +				dev_warn(&ssif_bmc->client->dev,
> +					 "Warn: Invalid request len");
> +
> +		} else {

You check msg_idx above, but I'm not sure that check will cover this
operation.

> +			buf[ssif_bmc->msg_idx - 1 +
> +			    ssif_bmc->request.len - ssif_bmc->recv_len]	= *val;
> +		}
> +
> +		ssif_bmc->msg_idx++;
> +
> +		break;
> +	default:
> +		/* Do not expect to go to this case */
> +		dev_err(&ssif_bmc->client->dev,
> +			"%s: Unexpected SMBus command 0x%x\n",
> +			__func__, ssif_bmc->smbus_cmd);
> +		break;
> +	}
> +}
> +
> +static bool validate_request(struct ssif_bmc_ctx *ssif_bmc)
> +{
> +	u8 rpec = 0, cpec = 0;
> +	bool ret = true;
> +	u8 addr, index;
> +	u8 *buf;
> +

Is there any length validation for using buf below?  It looks like you
are accessing without checking length, but maybe I missed something.

> +	buf = (u8 *)&ssif_bmc->request;
> +	switch (ssif_bmc->smbus_cmd) {
> +	case SSIF_IPMI_SINGLEPART_WRITE:
> +		if ((ssif_bmc->msg_idx - 1) == ssif_msg_len(&ssif_bmc->request)) {
> +			/* PEC is not included */
> +			ssif_bmc->pec_support = false;
> +			ret = true;
> +			goto exit;
> +		}
> +
> +		if ((ssif_bmc->msg_idx - 1) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
> +			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
> +				ssif_msg_len(&ssif_bmc->request));
> +			ret = false;
> +			goto exit;
> +		}
> +
> +		/* PEC is included */
> +		ssif_bmc->pec_support = true;
> +		rpec = buf[ssif_bmc->msg_idx - 2];
> +		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
> +		cpec = i2c_smbus_pec(cpec, &addr, 1);
> +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
> +		cpec = i2c_smbus_pec(cpec, buf, ssif_msg_len(&ssif_bmc->request));
> +		if (rpec != cpec) {
> +			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
> +			ret = false;
> +		}
> +
> +		break;
> +	case SSIF_IPMI_MULTIPART_WRITE_START:
> +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
> +	case SSIF_IPMI_MULTIPART_WRITE_END:
> +		index = ssif_bmc->request.len - ssif_bmc->recv_len;
> +		if ((ssif_bmc->msg_idx - 1 + index) == ssif_msg_len(&ssif_bmc->request)) {
> +			/* PEC is not included */
> +			ssif_bmc->pec_support = false;
> +			ret = true;
> +			goto exit;
> +		}
> +
> +		if ((ssif_bmc->msg_idx - 1 + index) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
> +			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
> +				ssif_msg_len(&ssif_bmc->request));
> +			ret = false;
> +			goto exit;
> +		}
> +
> +		/* PEC is included */
> +		ssif_bmc->pec_support = true;
> +		rpec = buf[ssif_bmc->msg_idx - 2 + index];
> +		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
> +		cpec = i2c_smbus_pec(cpec, &addr, 1);
> +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
> +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->recv_len, 1);

Just curious, I'm not sure the client side PEC in the Linux driver has
ever been validated.  Have you tested both sides?

> +		/* As SMBus specification does not allow the length
> +		 * (byte count) in the Write-Block protocol to be zero.
> +		 * Therefore, it is illegal to have the last Middle
> +		 * transaction in the sequence carry 32-byte and have
> +		 * a length of ‘0’ in the End transaction.
> +		 * But some users may try to use this way and we should
> +		 * prevent ssif_bmc driver broken in this case.
> +		 */
> +		if (ssif_bmc->recv_len != 0)
> +			cpec = i2c_smbus_pec(cpec, buf + 1 + index, ssif_bmc->recv_len);
> +
> +		if (rpec != cpec) {
> +			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
> +			ret = false;
> +		}
> +
> +		break;
> +	default:
> +		/* Do not expect to go to this case */
> +		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 0x%x\n",
> +			__func__, ssif_bmc->smbus_cmd);
> +		ret = false;
> +		break;
> +	}
> +
> +exit:
> +	return ret;
> +}
> +

Just a nit, more a general coding style comment.  It's almost always a
bad idea to put a negative (unsupported) into a check function.  You
often end up with something like:

	if (!unsupported_smbus_cmd(c))....

which looks a little strange.  Double negatives can make it hard to
follow and lead to mistakes.  This one isn't too bad, but sometimes it
can be.  It's better to do:

	if (supported_smbus_cmd(c))....
or
	if (!supported_smbus_cmd(c))....


> +static bool unsupported_smbus_cmd(u8 cmd)
> +{
> +	if (cmd == SSIF_IPMI_SINGLEPART_READ ||
> +	    cmd == SSIF_IPMI_SINGLEPART_WRITE ||
> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_END ||
> +	    cmd == SSIF_IPMI_MULTIPART_READ_START ||
> +	    cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
> +		return false;
> +
> +	return true;
> +}
> +
> +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	/* SMBUS command can vary (single or multi-part) */
> +	ssif_bmc->smbus_cmd = *val;
> +	ssif_bmc->msg_idx++;
> +
> +	if (unsupported_smbus_cmd(*val))
> +		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus command");
> +
> +	if (*val == SSIF_IPMI_SINGLEPART_WRITE ||
> +	    *val == SSIF_IPMI_MULTIPART_WRITE_START) {
> +		/*
> +		 * The response maybe not come in-time, causing host SSIF driver
> +		 * to timeout and resend a new request. In such case check for
> +		 * pending response and clear it
> +		 */
> +		if (ssif_bmc->response_in_progress)
> +			complete_response(ssif_bmc);
> +	}
> +}
> +
> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
> +	    ssif_bmc->state == SSIF_START ||
> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
> +	    ssif_bmc->state == SSIF_RES_SENDING) {
> +		ssif_bmc->state = SSIF_BAD_SMBUS;
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected READ REQUESTED in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +
> +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		ssif_bmc->state = SSIF_RES_SENDING;
> +	}
> +
> +	ssif_bmc->msg_idx = 0;
> +	if (ssif_bmc->is_singlepart_read)
> +		*val = ssif_bmc->response.len;
> +	else
> +		set_multipart_response_buffer(ssif_bmc, val);
> +}
> +
> +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
> +	    ssif_bmc->state == SSIF_START ||
> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
> +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected READ PROCESSED in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_BAD_SMBUS;
> +	}
> +
> +	handle_read_processed(ssif_bmc, val);
> +}
> +
> +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	ssif_bmc->msg_idx = 0;
> +
> +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		ssif_bmc->state = SSIF_START;
> +
> +	} else if (ssif_bmc->state == SSIF_START ||
> +		   ssif_bmc->state == SSIF_REQ_RECVING ||
> +		   ssif_bmc->state == SSIF_RES_SENDING) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected WRITE REQUEST in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_BAD_SMBUS;
> +	}
> +}
> +
> +static void on_write_received_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_RES_SENDING) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected WRITE RECEIVED in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +		ssif_bmc->state = SSIF_BAD_SMBUS;
> +	} else if (ssif_bmc->state == SSIF_START) {
> +		ssif_bmc->state = SSIF_SMBUS_CMD;
> +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		ssif_bmc->state = SSIF_REQ_RECVING;
> +	}
> +
> +	/* This is response sending state */
> +	if (ssif_bmc->state == SSIF_REQ_RECVING)
> +		handle_write_received(ssif_bmc, val);
> +	else if (ssif_bmc->state == SSIF_SMBUS_CMD)
> +		process_smbus_cmd(ssif_bmc, val);
> +}
> +
> +static void on_stop_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
> +	    ssif_bmc->state == SSIF_START ||
> +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected SLAVE STOP in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +
> +	} else if (ssif_bmc->state == SSIF_BAD_SMBUS) {
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s received SLAVE STOP from bad state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));
> +
> +	} else if (ssif_bmc->state == SSIF_REQ_RECVING) {
> +		/* A BMC that receives an invalid request drop the data for the write
> +		 * transaction and any further transactions (read or write) until
> +		 * the next valid read or write Start transaction is received
> +		 */
> +		if (!validate_request(ssif_bmc))
> +			dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
> +		else if (ssif_bmc->smbus_cmd == SSIF_IPMI_SINGLEPART_WRITE ||
> +			 ssif_bmc->smbus_cmd == SSIF_IPMI_MULTIPART_WRITE_END)
> +			handle_request(ssif_bmc);
> +	}
> +
> +	ssif_bmc->state = SSIF_READY;
> +	/* Reset message index */
> +	ssif_bmc->msg_idx = 0;
> +}
> +
> +/*
> + * Callback function to handle I2C slave events
> + */
> +static int ssif_bmc_cb(struct i2c_client *client, enum i2c_slave_event event, u8 *val)
> +{
> +	unsigned long flags;
> +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
> +	int ret = 0;
> +
> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> +
> +	switch (event) {
> +	case I2C_SLAVE_READ_REQUESTED:
> +		on_read_requested_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_WRITE_REQUESTED:
> +		on_write_requested_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_READ_PROCESSED:
> +		on_read_processed_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_WRITE_RECEIVED:
> +		on_write_received_event(ssif_bmc, val);
> +		break;
> +
> +	case I2C_SLAVE_STOP:
> +		on_stop_event(ssif_bmc, val);
> +		break;
> +
> +	default:
> +		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown i2c slave event\n");
> +		break;
> +	}
> +
> +	if (ssif_bmc->busy)
> +		ret = -EBUSY;
> +
> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> +
> +	return ret;
> +}
> +
> +static int ssif_bmc_probe(struct i2c_client *client, const struct i2c_device_id *id)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc;
> +	int ret;
> +
> +	ssif_bmc = devm_kzalloc(&client->dev, sizeof(*ssif_bmc), GFP_KERNEL);
> +	if (!ssif_bmc)
> +		return -ENOMEM;
> +
> +	spin_lock_init(&ssif_bmc->lock);
> +
> +	init_waitqueue_head(&ssif_bmc->wait_queue);
> +	ssif_bmc->request_available = false;
> +	ssif_bmc->response_in_progress = false;
> +	ssif_bmc->busy = false;
> +	ssif_bmc->response_timer_inited = false;
> +
> +	/* Register misc device interface */
> +	ssif_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
> +	ssif_bmc->miscdev.name = DEVICE_NAME;
> +	ssif_bmc->miscdev.fops = &ssif_bmc_fops;
> +	ssif_bmc->miscdev.parent = &client->dev;
> +	ret = misc_register(&ssif_bmc->miscdev);
> +	if (ret)
> +		goto out;
> +
> +	ssif_bmc->client = client;
> +	ssif_bmc->client->flags |= I2C_CLIENT_SLAVE;
> +
> +	/* Register I2C slave */
> +	i2c_set_clientdata(client, ssif_bmc);
> +	ret = i2c_slave_register(client, ssif_bmc_cb);
> +	if (ret) {
> +		misc_deregister(&ssif_bmc->miscdev);
> +		goto out;
> +	}
> +
> +	return 0;
> +out:
> +	devm_kfree(&client->dev, ssif_bmc);
> +	return ret;
> +}
> +
> +static int ssif_bmc_remove(struct i2c_client *client)
> +{
> +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
> +
> +	i2c_slave_unregister(client);
> +	misc_deregister(&ssif_bmc->miscdev);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id ssif_bmc_match[] = {
> +	{ .compatible = "ampere,ssif-bmc" },
> +	{ },
> +};
> +
> +static const struct i2c_device_id ssif_bmc_id[] = {
> +	{ DEVICE_NAME, 0 },
> +	{ },
> +};
> +
> +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
> +
> +static struct i2c_driver ssif_bmc_driver = {
> +	.driver         = {
> +		.name           = DEVICE_NAME,
> +		.of_match_table = ssif_bmc_match,
> +	},
> +	.probe          = ssif_bmc_probe,
> +	.remove         = ssif_bmc_remove,
> +	.id_table       = ssif_bmc_id,
> +};
> +
> +module_i2c_driver(ssif_bmc_driver);
> +
> +MODULE_AUTHOR("Quan Nguyen <[e-mail]>");
> +MODULE_AUTHOR("Chuong Tran <[e-mail]>");
> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF interface.");
> +MODULE_LICENSE("GPL");
> diff --git a/drivers/char/ipmi/ssif_bmc.h b/drivers/char/ipmi/ssif_bmc.h
> new file mode 100644
> index 000000000000..9a26f3c252cc
> --- /dev/null
> +++ b/drivers/char/ipmi/ssif_bmc.h
> @@ -0,0 +1,102 @@
> +/* SPDX-License-Identifier: GPL-2.0+ */
> +/*
> + * The driver for BMC side of SSIF interface
> + *
> + * Copyright (c) 2022, Ampere Computing LLC
> + *
> + */
> +#ifndef __SSIF_BMC_H__
> +#define __SSIF_BMC_H__
> +
> +#define DEVICE_NAME				"ipmi-ssif-host"
> +
> +#define GET_8BIT_ADDR(addr_7bit)		(((addr_7bit) << 1) & 0xff)
> +
> +/* A standard SMBus Transaction is limited to 32 data bytes */
> +#define MAX_PAYLOAD_PER_TRANSACTION		32
> +
> +#define MAX_IPMI_DATA_PER_START_TRANSACTION	30
> +#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION	31
> +
> +#define SSIF_IPMI_SINGLEPART_WRITE		0x2
> +#define SSIF_IPMI_SINGLEPART_READ		0x3
> +#define SSIF_IPMI_MULTIPART_WRITE_START		0x6
> +#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE	0x7
> +#define SSIF_IPMI_MULTIPART_WRITE_END		0x8
> +#define SSIF_IPMI_MULTIPART_READ_START		0x3
> +#define SSIF_IPMI_MULTIPART_READ_MIDDLE		0x9
> +
> +#define MSG_PAYLOAD_LEN_MAX			252
> +/*
> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
> + * Recover ssif_bmc from busy state if it takes upto 500ms
> + */
> +#define RESPONSE_TIMEOUT			500 /* ms */
> +
> +struct ssif_msg {
> +	u8 len;
> +	u8 netfn_lun;
> +	u8 cmd;
> +	u8 payload[MSG_PAYLOAD_LEN_MAX];
> +} __packed;
> +
> +static inline u32 ssif_msg_len(struct ssif_msg *ssif_msg)
> +{
> +	return ssif_msg->len + 1;
> +}
> +
> +/*
> + * SSIF internal states:
> + *   SSIF_READY         0x00 : Ready state
> + *   SSIF_START         0x01 : Start smbus transaction
> + *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
> + *   SSIF_REQ_RECVING   0x03 : Receiving request
> + *   SSIF_RES_SENDING   0x04 : Sending response
> + *   SSIF_BAD_SMBUS     0x05 : Bad SMbus transaction
> + */
> +enum ssif_state {
> +	SSIF_READY,
> +	SSIF_START,
> +	SSIF_SMBUS_CMD,
> +	SSIF_REQ_RECVING,
> +	SSIF_RES_SENDING,
> +	SSIF_BAD_SMBUS,
> +	SSIF_STATE_MAX
> +};
> +
> +struct ssif_bmc_ctx {
> +	struct i2c_client	*client;
> +	struct miscdevice	miscdev;
> +	size_t			msg_idx;
> +	bool			pec_support;
> +	/* ssif bmc spinlock */
> +	spinlock_t		lock;
> +	wait_queue_head_t	wait_queue;
> +	u8			running;
> +	enum ssif_state		state;
> +	u8			smbus_cmd;
> +	/* Timeout waiting for response */
> +	struct timer_list	response_timer;
> +	bool                    response_timer_inited;
> +	/* Flag to identify a Multi-part Read Transaction */
> +	bool			is_singlepart_read;
> +	u8			nbytes_processed;
> +	u8			remain_len;
> +	u8			recv_len;
> +	/* Block Number of a Multi-part Read Transaction */
> +	u8			block_num;
> +	bool			request_available;
> +	bool			response_in_progress;
> +	bool			busy;
> +	/* Response buffer for Multi-part Read Transaction */
> +	u8			response_buf[MAX_PAYLOAD_PER_TRANSACTION];
> +	struct ssif_msg		response;
> +	struct ssif_msg		request;
> +};
> +
> +static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
> +{
> +	return container_of(file->private_data, struct ssif_bmc_ctx, miscdev);
> +}
> +#endif /* __SSIF_BMC_H__ */
> -- 
> 2.35.1
> 
>

kernel test robot March 11, 2022, 6:20 a.m. UTC | #2

Hi Quan,

I love your patch! Perhaps something to improve:

[auto build test WARNING on char-misc/char-misc-testing]
[also build test WARNING on wsa/i2c/for-next cminyard-ipmi/for-next v5.17-rc7 next-20220310]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Quan-Nguyen/Add-SSIF-BMC-driver/20220310-194342
base:   https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git 3dd9a926ec2308e49445f22abef149fc64e9332e
config: mips-randconfig-s031-20220310 (https://download.01.org/0day-ci/archive/20220311/[e-mail]/config)
compiler: mips-linux-gcc (GCC) 11.2.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # apt-get install sparse
        # sparse version: v0.6.4-dirty
        # https://github.com/0day-ci/linux/commit/a977225b8997c2fdb51eddeee79de36075d3ce4d
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Quan-Nguyen/Add-SSIF-BMC-driver/20220310-194342
        git checkout a977225b8997c2fdb51eddeee79de36075d3ce4d
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' O=build_dir ARCH=mips SHELL=/bin/bash

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <[e-mail]>


sparse warnings: (new ones prefixed by >>)
   command-line: note: in included file:
   builtin:1:9: sparse: sparse: preprocessor token __ATOMIC_ACQUIRE redefined
   builtin:0:0: sparse: this was the original definition
   builtin:1:9: sparse: sparse: preprocessor token __ATOMIC_SEQ_CST redefined
   builtin:0:0: sparse: this was the original definition
   builtin:1:9: sparse: sparse: preprocessor token __ATOMIC_ACQ_REL redefined
   builtin:0:0: sparse: this was the original definition
   builtin:1:9: sparse: sparse: preprocessor token __ATOMIC_RELEASE redefined
   builtin:0:0: sparse: this was the original definition
>> drivers/char/ipmi/ssif_bmc.c:181:27: sparse: sparse: incorrect type in initializer (different base types) @@     expected restricted __poll_t ( *poll )( ... ) @@     got unsigned int ( * )( ... ) @@
   drivers/char/ipmi/ssif_bmc.c:181:27: sparse:     expected restricted __poll_t ( *poll )( ... )
   drivers/char/ipmi/ssif_bmc.c:181:27: sparse:     got unsigned int ( * )( ... )

vim +181 drivers/char/ipmi/ssif_bmc.c

   171	
   172	/*
   173	 * System calls to device interface for user apps
   174	 */
   175	static const struct file_operations ssif_bmc_fops = {
   176		.owner		= THIS_MODULE,
   177		.open		= ssif_bmc_open,
   178		.read		= ssif_bmc_read,
   179		.write		= ssif_bmc_write,
   180		.release	= ssif_bmc_release,
 > 181		.poll		= ssif_bmc_poll,
   182	};
   183	

---
0-DAY CI Kernel Test Service
https://lists.01.org/hyperkitty/list/[e-mail]

Jae Hyun Yoo March 14, 2022, 6:15 p.m. UTC | #3

Hi Quan,

[...]

> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> +{
> +	if (ssif_bmc->state == SSIF_READY ||
> +	    ssif_bmc->state == SSIF_START ||
> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
> +	    ssif_bmc->state == SSIF_RES_SENDING) {
> +		ssif_bmc->state = SSIF_BAD_SMBUS;
> +		dev_warn(&ssif_bmc->client->dev,
> +			 "Warn: %s unexpected READ REQUESTED in state=%s\n",
> +			 __func__, state_to_string(ssif_bmc->state));

It will print out that the case happens in SSIF_BAD_SMBUS state always
because ssif_bmc->state is already assigned as SSIF_BAD_SMBUS above.
Move the assignment to after the dev_warn printing.

[...]

> +static const struct of_device_id ssif_bmc_match[] = {
> +	{ .compatible = "ampere,ssif-bmc" },

Does this driver have any Ampere specific handling? If not, it could be
"ssif-bmc" as a generic SSIF driver.

> +	{ },
> +};

Add 'MODULE_DEVICE_TABLE(of, ssif_bmc_match);'

> +
> +static const struct i2c_device_id ssif_bmc_id[] = {
> +	{ DEVICE_NAME, 0 },
> +	{ },
> +};
> +

Remove this blank line.

> +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
> +
> +static struct i2c_driver ssif_bmc_driver = {
> +	.driver         = {
> +		.name           = DEVICE_NAME,
> +		.of_match_table = ssif_bmc_match,
> +	},
> +	.probe          = ssif_bmc_probe,
> +	.remove         = ssif_bmc_remove,
> +	.id_table       = ssif_bmc_id,
> +};
> +

Remove this blank line too.

-Jae

> +module_i2c_driver(ssif_bmc_driver);
> +
> +MODULE_AUTHOR("Quan Nguyen <[e-mail]>");
> +MODULE_AUTHOR("Chuong Tran <[e-mail]>");
> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF interface.");
> +MODULE_LICENSE("GPL");

[...]

Quan Nguyen March 17, 2022, 8:30 a.m. UTC | #4

On 11/03/2022 08:19, Corey Minyard wrote:
> On Thu, Mar 10, 2022 at 06:41:16PM +0700, Quan Nguyen wrote:
>> The SMBus system interface (SSIF) IPMI BMC driver can be used to perform
>> in-band IPMI communication with their host in management (BMC) side.
> 
> Thanks for the update, and removing slave_enable().
> 
> I spent some quality time with this, and it looks like there are places
> where you don't check lengths before indexing arrays.  I've marked
> several of these, but you need to check it all through this.
> 
> I have a few other comments, too.
> 
Thank you for the comments, I put my comment inline below.
I'll scan the code and may put some extra fixes if any in next version.

> -corey
> 
>>
>> Signed-off-by: Quan Nguyen <[e-mail]>
>> ---
>> v6:
>>    + Drop the use of slave_enable()                             [Wolfram]
>>    + Make i2c-aspeed to issue RxCmdLast command on all
>>    I2C_SLAVE_WRITE_REQUESTED event to assert NAK when slave busy   [Quan]
>>    + Make i2c slave to return -EBUSY when it's busy                [Quan]
>>    + Drop the aborting feature as return Completion Code 0xFF may stop
>>    host to retry and make ipmi_ssif.so fails to load               [Quan]
>>    + Add timer to recover slave from busy state when no response   [Quan]
>>    + Clean request/response buffer appropriately                   [Quan]
>>    + Add some minor change on error and warning messages           [Quan]
>>
>> v5:
>>    + None
>>
>> v4:
>>    + Send response with Completion code 0xFF when aborting         [Quan]
>>    + Added bounding check on SMBus writes and the whole request     [Dan]
>>    + Moved buffer to end of struct ssif_bmc_ctx to avoid context
>>      corruption if somehow buffer is written past the end           [Dan]
>>    + Return -EINVAL if userspace buffer too small, dont
>>      silence truncate                                       [Corey, Joel]
>>    + Not necessary to check NONBLOCK in lock                      [Corey]
>>    + Enforce one user at a time                                    [Joel]
>>    + Reject write with invalid response length from userspace     [Corey]
>>    + Add state machines for better ssif bmc state handling         [Quan]
>>    + Drop ssif_bmc_aspeed.c and make ssif_bmc.c is generic
>>      SSIF BMC driver                                               [Quan]
>>    + Change compatible string "aspeed,ast2500-ssif-bmc" to
>>      "ampere,ssif-bmc"                                             [Quan]
>>    + Abort current request with invalid SMBus write or
>>      invalid command                                               [Quan]
>>    + Abort all request if there is pending response                [Quan]
>>    + Changed validate_pec() to validate_request()                  [Quan]
>>    + Add unsupported_smbus_cmd() to handle unknown SMBus command   [Quan]
>>    + Print internal state string for ease investigating issue      [Quan]
>>    + Move to READY state on SLAVE_STOP event                       [Quan]
>>    + Change initilize_transfer() to process_smbus_cmd()            [Quan]
>>    + Introduce functions for each slave event                      [Quan]
>>
>> v3:
>>    + Removed redundant license info                                [Joel]
>>    + Switched to use traditional if-else                           [Joel]
>>    + Removed unused ssif_bmc_ioctl()                               [Joel]
>>    + Made handle_request()/complete_response() to return void      [Joel]
>>    + Refactored send_ssif_bmc_response() and
>>    receive_ssif_bmc_request()                                     [Corey]
>>    + Removed mutex                                                [Corey]
>>    + Use spin_lock/unlock_irqsave/restore in callback             [Corey]
>>    + Removed the unnecessary memset                               [Corey]
>>    + Switch to use dev_err()                                      [Corey]
>>
>> v2:
>>    + Fixed compiling error with COMPILE_TEST for arc
>>
>>   drivers/char/ipmi/Kconfig    |  11 +
>>   drivers/char/ipmi/Makefile   |   1 +
>>   drivers/char/ipmi/ssif_bmc.c | 791 +++++++++++++++++++++++++++++++++++
>>   drivers/char/ipmi/ssif_bmc.h | 102 +++++
>>   4 files changed, 905 insertions(+)
>>   create mode 100644 drivers/char/ipmi/ssif_bmc.c
>>   create mode 100644 drivers/char/ipmi/ssif_bmc.h
>>
>> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
>> index b061e6b513ed..18a89093d64e 100644
>> --- a/drivers/char/ipmi/Kconfig
>> +++ b/drivers/char/ipmi/Kconfig
>> @@ -169,6 +169,17 @@ config ASPEED_BT_IPMI_BMC
>>   	  found on Aspeed SOCs (AST2400 and AST2500). The driver
>>   	  implements the BMC side of the BT interface.
>>   
>> +config SSIF_IPMI_BMC
>> +	tristate "SSIF IPMI BMC driver"
>> +	select I2C
>> +	select I2C_SLAVE
>> +	help
>> +	  This enables the IPMI SMBus system interface (SSIF) at the
>> +	  management (BMC) side.
>> +
>> +	  The driver implements the BMC side of the SMBus system
>> +	  interface (SSIF).
>> +
>>   config IPMB_DEVICE_INTERFACE
>>   	tristate 'IPMB Interface handler'
>>   	depends on I2C
>> diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
>> index 7ce790efad92..cb6138b8ded9 100644
>> --- a/drivers/char/ipmi/Makefile
>> +++ b/drivers/char/ipmi/Makefile
>> @@ -30,3 +30,4 @@ 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
>> +obj-$(CONFIG_SSIF_IPMI_BMC) += ssif_bmc.o
>> diff --git a/drivers/char/ipmi/ssif_bmc.c b/drivers/char/ipmi/ssif_bmc.c
>> new file mode 100644
>> index 000000000000..62db97773654
>> --- /dev/null
>> +++ b/drivers/char/ipmi/ssif_bmc.c
>> @@ -0,0 +1,791 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * The driver for BMC side of SSIF interface
>> + *
>> + * Copyright (c) 2022, Ampere Computing LLC
>> + *
>> + */
>> +
>> +#include <linux/i2c.h>
>> +#include <linux/miscdevice.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/poll.h>
>> +#include <linux/sched.h>
>> +#include <linux/mutex.h>
>> +#include <linux/spinlock.h>
>> +#include <linux/timer.h>
>> +#include <linux/jiffies.h>
>> +
>> +#include "ssif_bmc.h"
>> +
>> +static const char *state_to_string(enum ssif_state state)
>> +{
>> +	switch (state) {
>> +	case SSIF_READY:
>> +		return "SSIF_READY";
>> +	case SSIF_START:
>> +		return "SSIF_START";
>> +	case SSIF_SMBUS_CMD:
>> +		return "SSIF_SMBUS_CMD";
>> +	case SSIF_REQ_RECVING:
>> +		return "SSIF_REQ_RECVING";
>> +	case SSIF_RES_SENDING:
>> +		return "SSIF_RES_SENDING";
>> +	case SSIF_BAD_SMBUS:
>> +		return "SSIF_BAD_SMBUS";
>> +	default:
>> +		return "SSIF_STATE_UNKNOWN";
>> +	}
>> +}
>> +
>> +/* Handle SSIF message that will be sent to user */
>> +static ssize_t ssif_bmc_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	struct ssif_msg msg;
>> +	unsigned long flags;
>> +	ssize_t ret;
>> +
>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	while (!ssif_bmc->request_available) {
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +		if (file->f_flags & O_NONBLOCK)
>> +			return -EAGAIN;
>> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
>> +					       ssif_bmc->request_available);
>> +		if (ret)
>> +			return ret;
>> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	}
>> +
>> +	if (count < min_t(ssize_t, ssif_msg_len(&ssif_bmc->request), sizeof(struct ssif_msg))) {
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +		ret = -EINVAL;
>> +	} else {
>> +		count = min_t(ssize_t, ssif_msg_len(&ssif_bmc->request), sizeof(struct ssif_msg));
>> +		memcpy(&msg, &ssif_bmc->request, count);
>> +		ssif_bmc->request_available = false;
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +		ret = copy_to_user(buf, &msg, count);
>> +	}
>> +
>> +	return (ret < 0) ? ret : count;
>> +}
>> +
>> +/* Handle SSIF message that is written by user */
>> +static ssize_t ssif_bmc_write(struct file *file, const char __user *buf, size_t count,
>> +			      loff_t *ppos)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	struct ssif_msg msg;
>> +	unsigned long flags;
>> +	ssize_t ret;
>> +
>> +	if (count > sizeof(struct ssif_msg))
>> +		return -EINVAL;
>> +
>> +	ret = copy_from_user(&msg, buf, count);
>> +	if (ret)
>> +		return ret;
>> +
>> +	if (!msg.len || count < ssif_msg_len(&msg))
>> +		return -EINVAL;
>> +
>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	while (ssif_bmc->response_in_progress) {
>> +		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +		if (file->f_flags & O_NONBLOCK)
>> +			return -EAGAIN;
>> +		ret = wait_event_interruptible(ssif_bmc->wait_queue,
>> +					       !ssif_bmc->response_in_progress);
>> +		if (ret)
>> +			return ret;
>> +		spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +	}
>> +
>> +	memcpy(&ssif_bmc->response, &msg, count);
>> +	ssif_bmc->is_singlepart_read = (ssif_msg_len(&msg) <= MAX_PAYLOAD_PER_TRANSACTION + 1);
>> +
>> +	ssif_bmc->response_in_progress = true;
>> +
>> +	/* ssif_bmc not busy */
>> +	ssif_bmc->busy = false;
>> +
>> +	if (ssif_bmc->response_timer_inited) {
>> +		del_timer(&ssif_bmc->response_timer);
>> +		ssif_bmc->response_timer_inited = false;
>> +	}
>> +	/* Clean old request buffer */
>> +	memset(&ssif_bmc->request, 0, sizeof(struct ssif_msg));
>> +
>> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +	return count;
>> +}
>> +
>> +static int ssif_bmc_open(struct inode *inode, struct file *file)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	int ret = 0;
>> +
>> +	spin_lock_irq(&ssif_bmc->lock);
>> +	if (!ssif_bmc->running)
>> +		ssif_bmc->running = 1;
>> +	else
>> +		ret = -EBUSY;
>> +	spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +	return ret;
>> +}
>> +
>> +static unsigned int ssif_bmc_poll(struct file *file, poll_table *wait)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +	unsigned int mask = 0;
>> +
>> +	poll_wait(file, &ssif_bmc->wait_queue, wait);
>> +
>> +	spin_lock_irq(&ssif_bmc->lock);
>> +	/* The request is available, userspace application can get the request */
>> +	if (ssif_bmc->request_available)
>> +		mask |= POLLIN;
>> +
>> +	spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +	return mask;
>> +}
>> +
>> +static int ssif_bmc_release(struct inode *inode, struct file *file)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +
>> +	spin_lock_irq(&ssif_bmc->lock);
>> +	ssif_bmc->running = 0;
>> +	spin_unlock_irq(&ssif_bmc->lock);
>> +
>> +	return 0;
>> +}
>> +
>> +/*
>> + * System calls to device interface for user apps
>> + */
>> +static const struct file_operations ssif_bmc_fops = {
>> +	.owner		= THIS_MODULE,
>> +	.open		= ssif_bmc_open,
>> +	.read		= ssif_bmc_read,
>> +	.write		= ssif_bmc_write,
>> +	.release	= ssif_bmc_release,
>> +	.poll		= ssif_bmc_poll,
>> +};
>> +
>> +/* Called with ssif_bmc->lock held. */
>> +static void complete_response(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +	/* Invalidate response in buffer to denote it having been sent. */
>> +	ssif_bmc->response.len = 0;
>> +	ssif_bmc->response_in_progress = false;
>> +	ssif_bmc->nbytes_processed = 0;
>> +	ssif_bmc->remain_len = 0;
>> +	ssif_bmc->busy = false;
>> +	memset(&ssif_bmc->response_buf, 0, MAX_PAYLOAD_PER_TRANSACTION);
>> +	wake_up_all(&ssif_bmc->wait_queue);
>> +}
>> +
>> +static void response_timeout(struct timer_list *t)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, response_timer);
>> +	unsigned long flags;
>> +
> 
> Is there a possible race here?  The timeout can happen at the same time
> as a received message, will something bad happen if that's the case?
> 

Thanks Corey,
I think I need extra comment here.

The purpose of this timeout is to make sure ssif_bmc will recover from 
busy state in case the upper stack does not provide the response.
Hence, the response timeout is set as 500ms, twice the time of max 
Request-to-Response in spec as the code below. Should it be longer?

As per spec, the max Request-to-Respose would not exceed 250ms.

I put the comment in ssif_bmc.h as below:
 >> +/*
 >> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
 >> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
 >> + * Recover ssif_bmc from busy state if it takes upto 500ms
 >> + */
 >> +#define RESPONSE_TIMEOUT			500 /* ms */


>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +
>> +	/* Recover ssif_bmc from busy */
>> +	ssif_bmc->busy = false;
>> +	del_timer(&ssif_bmc->response_timer);
> 
> You don't need to delete the timer, it's in the timeout.
> 

Will remove this redundant code in next version

>> +	ssif_bmc->response_timer_inited = false;
>> +
>> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +}
>> +
>> +/* Called with ssif_bmc->lock held. */
>> +static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +	/* set ssif_bmc to busy waiting for response */
>> +	ssif_bmc->busy = true;
>> +
>> +	/* Request message is available to process */
>> +	ssif_bmc->request_available = true;
>> +
>> +	/* Clean old response buffer */
>> +	memset(&ssif_bmc->response, 0, sizeof(struct ssif_msg));
>> +
>> +	/* This is the new READ request.*/
>> +	wake_up_all(&ssif_bmc->wait_queue);
>> +
>> +	/* Armed timer to recover slave from busy state in case of no response */
>> +	if (!ssif_bmc->response_timer_inited) {
>> +		timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
>> +		ssif_bmc->response_timer_inited = true;
>> +	}
>> +	mod_timer(&ssif_bmc->response_timer, jiffies + msecs_to_jiffies(RESPONSE_TIMEOUT));
>> +}
>> +
>> +static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	u8 response_len = 0;
>> +	int idx = 0;
>> +	u8 data_len;
>> +
>> +	data_len = ssif_bmc->response.len;
>> +	switch (ssif_bmc->smbus_cmd) {
>> +	case SSIF_IPMI_MULTIPART_READ_START:
>> +		/*
>> +		 * Read Start length is 32 bytes.
>> +		 * Read Start transfer first 30 bytes of IPMI response
>> +		 * and 2 special code 0x00, 0x01.
>> +		 */
>> +		*val = MAX_PAYLOAD_PER_TRANSACTION;
>> +		ssif_bmc->remain_len = data_len - MAX_IPMI_DATA_PER_START_TRANSACTION;
>> +		ssif_bmc->block_num = 0;
> 
> Do you need to validate the data length before using this?
> This applies for lots of places through here.
> 

set_multipart_response_buffer() is called only when ->is_singlepart_read 
is false, which is determined by the below code under the *_write()

ssif_bmc->is_singlepart_read = (ssif_msg_len(&msg) <= 
MAX_PAYLOAD_PER_TRANSACTION + 1);

So, I think the len is validated and could be use in this functions.

>> +
>> +		ssif_bmc->response_buf[idx++] = 0x00; /* Start Flag */
>> +		ssif_bmc->response_buf[idx++] = 0x01; /* Start Flag */
>> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.netfn_lun;
>> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.cmd;
>> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.payload[0];
>> +
>> +		response_len = MAX_PAYLOAD_PER_TRANSACTION - idx;
>> +
>> +		memcpy(&ssif_bmc->response_buf[idx], &ssif_bmc->response.payload[1],
>> +		       response_len);
>> +		break;
>> +
>> +	case SSIF_IPMI_MULTIPART_READ_MIDDLE:
>> +		/*
>> +		 * IPMI READ Middle or READ End messages can carry up to 31 bytes
>> +		 * IPMI data plus block number byte.
>> +		 */
>> +		if (ssif_bmc->remain_len < MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
>> +			/*
>> +			 * This is READ End message
>> +			 *  Return length is the remaining response data length
>> +			 *  plus block number
>> +			 *  Block number 0xFF is to indicate this is last message
>> +			 *
>> +			 */
>> +			*val = ssif_bmc->remain_len + 1;
>> +			ssif_bmc->block_num = 0xFF;
>> +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
>> +			response_len = ssif_bmc->remain_len;
>> +			/* Clean the buffer */
>> +			memset(&ssif_bmc->response_buf[idx], 0, MAX_PAYLOAD_PER_TRANSACTION - idx);
>> +		} else {
>> +			/*
>> +			 * This is READ Middle message
>> +			 *  Response length is the maximum SMBUS transfer length
>> +			 *  Block number byte is incremented
>> +			 * Return length is maximum SMBUS transfer length
>> +			 */
>> +			*val = MAX_PAYLOAD_PER_TRANSACTION;
>> +			ssif_bmc->remain_len -= MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>> +			response_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>> +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
>> +			ssif_bmc->block_num++;
>> +		}
>> +
>> +		memcpy(&ssif_bmc->response_buf[idx],
>> +		       ssif_bmc->response.payload + 1 + ssif_bmc->nbytes_processed,
>> +		       response_len);
>> +		break;
>> +
>> +	default:
>> +		/* Do not expect to go to this case */
>> +		dev_err(&ssif_bmc->client->dev,
>> +			"%s: Unexpected SMBus command 0x%x\n",
>> +			__func__, ssif_bmc->smbus_cmd);
>> +		break;
>> +	}
>> +
>> +	ssif_bmc->nbytes_processed += response_len;
>> +}
>> +
>> +/* Process the IPMI response that will be read by master */
>> +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	u8 *buf;
>> +	u8 pec_len, addr, len;
>> +	u8 pec = 0;
>> +
>> +	pec_len = ssif_bmc->pec_support ? 1 : 0;
>> +	/* PEC - Start Read Address */
>> +	addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +	pec = i2c_smbus_pec(pec, &addr, 1);
>> +	/* PEC - SSIF Command */
>> +	pec = i2c_smbus_pec(pec, &ssif_bmc->smbus_cmd, 1);
>> +	/* PEC - Restart Write Address */
>> +	addr = addr | 0x01;
>> +	pec = i2c_smbus_pec(pec, &addr, 1);
>> +
>> +	if (ssif_bmc->is_singlepart_read) {
>> +		/* Single-part Read processing */
>> +		buf = (u8 *)&ssif_bmc->response;
>> +
>> +		if (ssif_bmc->response.len && ssif_bmc->msg_idx < ssif_bmc->response.len) {
>> +			ssif_bmc->msg_idx++;
>> +			*val = buf[ssif_bmc->msg_idx];
>> +		} else if (ssif_bmc->response.len && ssif_bmc->msg_idx == ssif_bmc->response.len) {
>> +			ssif_bmc->msg_idx++;
>> +			*val = i2c_smbus_pec(pec, buf, ssif_msg_len(&ssif_bmc->response));
>> +		} else {
> 
> I thought for a second that this was wrong, but I think it's correct.
> Supply zero if you don't have data.
> 
>> +			*val = 0;
>> +		}
>> +		/* Invalidate response buffer to denote it is sent */
>> +		if (ssif_bmc->msg_idx + 1 >= (ssif_msg_len(&ssif_bmc->response) + pec_len))
>> +			complete_response(ssif_bmc);
>> +	} else {
>> +		/* Multi-part Read processing */
> 
> You don't check the length here like you did above.  I think that's
> required.
> 

As per my explanation above, the ->is_singlepart_read is determined by 
testing the length, so it is validated as I assumed.

>> +		switch (ssif_bmc->smbus_cmd) {
>> +		case SSIF_IPMI_MULTIPART_READ_START:
>> +		case SSIF_IPMI_MULTIPART_READ_MIDDLE:
>> +			buf = (u8 *)&ssif_bmc->response_buf;
>> +			*val = buf[ssif_bmc->msg_idx];
>> +			ssif_bmc->msg_idx++;
>> +			break;
>> +		default:
>> +			/* Do not expect to go to this case */
>> +			dev_err(&ssif_bmc->client->dev,
>> +				"%s: Unexpected SMBus command 0x%x\n",
>> +				__func__, ssif_bmc->smbus_cmd);
>> +			break;
>> +		}
>> +
>> +		len = (ssif_bmc->block_num == 0xFF) ?
>> +		       ssif_bmc->remain_len + 1 : MAX_PAYLOAD_PER_TRANSACTION;
>> +		if (ssif_bmc->msg_idx == (len + 1)) {
>> +			pec = i2c_smbus_pec(pec, &len, 1);
>> +			*val = i2c_smbus_pec(pec, ssif_bmc->response_buf, len);
>> +		}
>> +		/* Invalidate response buffer to denote last response is sent */
>> +		if (ssif_bmc->block_num == 0xFF &&
>> +		    ssif_bmc->msg_idx > (ssif_bmc->remain_len + pec_len)) {
>> +			complete_response(ssif_bmc);
>> +		}
>> +	}
>> +}
>> +
>> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	u8 *buf = (u8 *)&ssif_bmc->request;
>> +
>> +	if (ssif_bmc->msg_idx >= sizeof(struct ssif_msg))
>> +		return;
>> +
>> +	switch (ssif_bmc->smbus_cmd) {
>> +	case SSIF_IPMI_SINGLEPART_WRITE:
>> +		buf[ssif_bmc->msg_idx - 1] = *val;
>> +		ssif_bmc->msg_idx++;
>> +
>> +		break;
>> +	case SSIF_IPMI_MULTIPART_WRITE_START:
>> +		if (ssif_bmc->msg_idx == 1)
>> +			ssif_bmc->request.len = 0;
>> +
>> +		fallthrough;
>> +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
>> +		/* The len should always be 32 */
>> +		if (ssif_bmc->msg_idx == 1 && *val != MAX_PAYLOAD_PER_TRANSACTION)
>> +			dev_warn(&ssif_bmc->client->dev,
>> +				 "Warn: Invalid Multipart Write len");
>> +
>> +		fallthrough;
>> +	case SSIF_IPMI_MULTIPART_WRITE_END:
>> +		/* Multi-part write, 2nd byte received is length */
>> +		if (ssif_bmc->msg_idx == 1) {
>> +			if (*val > MAX_PAYLOAD_PER_TRANSACTION)
>> +				dev_warn(&ssif_bmc->client->dev,
>> +					 "Warn: Invalid Multipart Write End len");
>> +
>> +			ssif_bmc->request.len += *val;
>> +			ssif_bmc->recv_len = *val;
>> +
>> +			/* request len should never exceeded 255 bytes */
>> +			if (ssif_bmc->request.len > 255)
>> +				dev_warn(&ssif_bmc->client->dev,
>> +					 "Warn: Invalid request len");
>> +
>> +		} else {
> 
> You check msg_idx above, but I'm not sure that check will cover this
> operation.
> 
That check is to make sure the length (*val) must always be strictly 32 
bytes in case of MULTIPART_WRITE_START/MIDDLE. And this check allows the 
length is up to 32 bytes in MULTIPART_WRITE_END.

>> +			buf[ssif_bmc->msg_idx - 1 +
>> +			    ssif_bmc->request.len - ssif_bmc->recv_len]	= *val;
>> +		}
>> +
>> +		ssif_bmc->msg_idx++;
>> +
>> +		break;
>> +	default:
>> +		/* Do not expect to go to this case */
>> +		dev_err(&ssif_bmc->client->dev,
>> +			"%s: Unexpected SMBus command 0x%x\n",
>> +			__func__, ssif_bmc->smbus_cmd);
>> +		break;
>> +	}
>> +}
>> +
>> +static bool validate_request(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +	u8 rpec = 0, cpec = 0;
>> +	bool ret = true;
>> +	u8 addr, index;
>> +	u8 *buf;
>> +
> 
> Is there any length validation for using buf below?  It looks like you
> are accessing without checking length, but maybe I missed something.
> 

Yes, there is length testing for each part before using buf to calculate 
PEC as in the "if" below.

>> +	buf = (u8 *)&ssif_bmc->request;
>> +	switch (ssif_bmc->smbus_cmd) {
>> +	case SSIF_IPMI_SINGLEPART_WRITE:
>> +		if ((ssif_bmc->msg_idx - 1) == ssif_msg_len(&ssif_bmc->request)) {
>> +			/* PEC is not included */
>> +			ssif_bmc->pec_support = false;
>> +			ret = true;
>> +			goto exit;
>> +		}
>> +
>> +		if ((ssif_bmc->msg_idx - 1) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
>> +			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
>> +				ssif_msg_len(&ssif_bmc->request));
>> +			ret = false;
>> +			goto exit;
>> +		}
>> +
>> +		/* PEC is included */
>> +		ssif_bmc->pec_support = true;
>> +		rpec = buf[ssif_bmc->msg_idx - 2];
>> +		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +		cpec = i2c_smbus_pec(cpec, &addr, 1);
>> +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
>> +		cpec = i2c_smbus_pec(cpec, buf, ssif_msg_len(&ssif_bmc->request));
>> +		if (rpec != cpec) {
>> +			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
>> +			ret = false;
>> +		}
>> +
>> +		break;
>> +	case SSIF_IPMI_MULTIPART_WRITE_START:
>> +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
>> +	case SSIF_IPMI_MULTIPART_WRITE_END:
>> +		index = ssif_bmc->request.len - ssif_bmc->recv_len;
>> +		if ((ssif_bmc->msg_idx - 1 + index) == ssif_msg_len(&ssif_bmc->request)) {
>> +			/* PEC is not included */
>> +			ssif_bmc->pec_support = false;
>> +			ret = true;
>> +			goto exit;
>> +		}
>> +
>> +		if ((ssif_bmc->msg_idx - 1 + index) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
>> +			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
>> +				ssif_msg_len(&ssif_bmc->request));
>> +			ret = false;
>> +			goto exit;
>> +		}
>> +
>> +		/* PEC is included */
>> +		ssif_bmc->pec_support = true;
>> +		rpec = buf[ssif_bmc->msg_idx - 2 + index];
>> +		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +		cpec = i2c_smbus_pec(cpec, &addr, 1);
>> +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
>> +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->recv_len, 1);
> 
> Just curious, I'm not sure the client side PEC in the Linux driver has
> ever been validated.  Have you tested both sides?
> 

Yes, we found that request from host has an extra byte for PEC and that 
is why we added PEC support.

>> +		/* As SMBus specification does not allow the length
>> +		 * (byte count) in the Write-Block protocol to be zero.
>> +		 * Therefore, it is illegal to have the last Middle
>> +		 * transaction in the sequence carry 32-byte and have
>> +		 * a length of ‘0’ in the End transaction.
>> +		 * But some users may try to use this way and we should
>> +		 * prevent ssif_bmc driver broken in this case.
>> +		 */
>> +		if (ssif_bmc->recv_len != 0)
>> +			cpec = i2c_smbus_pec(cpec, buf + 1 + index, ssif_bmc->recv_len);
>> +
>> +		if (rpec != cpec) {
>> +			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
>> +			ret = false;
>> +		}
>> +
>> +		break;
>> +	default:
>> +		/* Do not expect to go to this case */
>> +		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 0x%x\n",
>> +			__func__, ssif_bmc->smbus_cmd);
>> +		ret = false;
>> +		break;
>> +	}
>> +
>> +exit:
>> +	return ret;
>> +}
>> +
> 
> Just a nit, more a general coding style comment.  It's almost always a
> bad idea to put a negative (unsupported) into a check function.  You
> often end up with something like:
> 
> 	if (!unsupported_smbus_cmd(c))....
> 
> which looks a little strange.  Double negatives can make it hard to
> follow and lead to mistakes.  This one isn't too bad, but sometimes it
> can be.  It's better to do:
> 
> 	if (supported_smbus_cmd(c))....
> or
> 	if (!supported_smbus_cmd(c))....
> 
> 

Thanks, Corey. I'll try to refactor this part in next version.

>> +static bool unsupported_smbus_cmd(u8 cmd)
>> +{
>> +	if (cmd == SSIF_IPMI_SINGLEPART_READ ||
>> +	    cmd == SSIF_IPMI_SINGLEPART_WRITE ||
>> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
>> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
>> +	    cmd == SSIF_IPMI_MULTIPART_WRITE_END ||
>> +	    cmd == SSIF_IPMI_MULTIPART_READ_START ||
>> +	    cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
>> +		return false;
>> +
>> +	return true;
>> +}
>> +
>> +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	/* SMBUS command can vary (single or multi-part) */
>> +	ssif_bmc->smbus_cmd = *val;
>> +	ssif_bmc->msg_idx++;
>> +
>> +	if (unsupported_smbus_cmd(*val))
>> +		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus command");
>> +
>> +	if (*val == SSIF_IPMI_SINGLEPART_WRITE ||
>> +	    *val == SSIF_IPMI_MULTIPART_WRITE_START) {
>> +		/*
>> +		 * The response maybe not come in-time, causing host SSIF driver
>> +		 * to timeout and resend a new request. In such case check for
>> +		 * pending response and clear it
>> +		 */
>> +		if (ssif_bmc->response_in_progress)
>> +			complete_response(ssif_bmc);
>> +	}
>> +}
>> +
>> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	if (ssif_bmc->state == SSIF_READY ||
>> +	    ssif_bmc->state == SSIF_START ||
>> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
>> +	    ssif_bmc->state == SSIF_RES_SENDING) {
>> +		ssif_bmc->state = SSIF_BAD_SMBUS;
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected READ REQUESTED in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +
>> +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +		ssif_bmc->state = SSIF_RES_SENDING;
>> +	}
>> +
>> +	ssif_bmc->msg_idx = 0;
>> +	if (ssif_bmc->is_singlepart_read)
>> +		*val = ssif_bmc->response.len;
>> +	else
>> +		set_multipart_response_buffer(ssif_bmc, val);
>> +}
>> +
>> +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	if (ssif_bmc->state == SSIF_READY ||
>> +	    ssif_bmc->state == SSIF_START ||
>> +	    ssif_bmc->state == SSIF_REQ_RECVING ||
>> +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected READ PROCESSED in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +		ssif_bmc->state = SSIF_BAD_SMBUS;
>> +	}
>> +
>> +	handle_read_processed(ssif_bmc, val);
>> +}
>> +
>> +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	ssif_bmc->msg_idx = 0;
>> +
>> +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +		ssif_bmc->state = SSIF_START;
>> +
>> +	} else if (ssif_bmc->state == SSIF_START ||
>> +		   ssif_bmc->state == SSIF_REQ_RECVING ||
>> +		   ssif_bmc->state == SSIF_RES_SENDING) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected WRITE REQUEST in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +		ssif_bmc->state = SSIF_BAD_SMBUS;
>> +	}
>> +}
>> +
>> +static void on_write_received_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_RES_SENDING) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected WRITE RECEIVED in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +		ssif_bmc->state = SSIF_BAD_SMBUS;
>> +	} else if (ssif_bmc->state == SSIF_START) {
>> +		ssif_bmc->state = SSIF_SMBUS_CMD;
>> +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +		ssif_bmc->state = SSIF_REQ_RECVING;
>> +	}
>> +
>> +	/* This is response sending state */
>> +	if (ssif_bmc->state == SSIF_REQ_RECVING)
>> +		handle_write_received(ssif_bmc, val);
>> +	else if (ssif_bmc->state == SSIF_SMBUS_CMD)
>> +		process_smbus_cmd(ssif_bmc, val);
>> +}
>> +
>> +static void on_stop_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +	if (ssif_bmc->state == SSIF_READY ||
>> +	    ssif_bmc->state == SSIF_START ||
>> +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s unexpected SLAVE STOP in state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +
>> +	} else if (ssif_bmc->state == SSIF_BAD_SMBUS) {
>> +		dev_warn(&ssif_bmc->client->dev,
>> +			 "Warn: %s received SLAVE STOP from bad state=%s\n",
>> +			 __func__, state_to_string(ssif_bmc->state));
>> +
>> +	} else if (ssif_bmc->state == SSIF_REQ_RECVING) {
>> +		/* A BMC that receives an invalid request drop the data for the write
>> +		 * transaction and any further transactions (read or write) until
>> +		 * the next valid read or write Start transaction is received
>> +		 */
>> +		if (!validate_request(ssif_bmc))
>> +			dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
>> +		else if (ssif_bmc->smbus_cmd == SSIF_IPMI_SINGLEPART_WRITE ||
>> +			 ssif_bmc->smbus_cmd == SSIF_IPMI_MULTIPART_WRITE_END)
>> +			handle_request(ssif_bmc);
>> +	}
>> +
>> +	ssif_bmc->state = SSIF_READY;
>> +	/* Reset message index */
>> +	ssif_bmc->msg_idx = 0;
>> +}
>> +
>> +/*
>> + * Callback function to handle I2C slave events
>> + */
>> +static int ssif_bmc_cb(struct i2c_client *client, enum i2c_slave_event event, u8 *val)
>> +{
>> +	unsigned long flags;
>> +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
>> +	int ret = 0;
>> +
>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>> +
>> +	switch (event) {
>> +	case I2C_SLAVE_READ_REQUESTED:
>> +		on_read_requested_event(ssif_bmc, val);
>> +		break;
>> +
>> +	case I2C_SLAVE_WRITE_REQUESTED:
>> +		on_write_requested_event(ssif_bmc, val);
>> +		break;
>> +
>> +	case I2C_SLAVE_READ_PROCESSED:
>> +		on_read_processed_event(ssif_bmc, val);
>> +		break;
>> +
>> +	case I2C_SLAVE_WRITE_RECEIVED:
>> +		on_write_received_event(ssif_bmc, val);
>> +		break;
>> +
>> +	case I2C_SLAVE_STOP:
>> +		on_stop_event(ssif_bmc, val);
>> +		break;
>> +
>> +	default:
>> +		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown i2c slave event\n");
>> +		break;
>> +	}
>> +
>> +	if (ssif_bmc->busy)
>> +		ret = -EBUSY;
>> +
>> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +	return ret;
>> +}
>> +
>> +static int ssif_bmc_probe(struct i2c_client *client, const struct i2c_device_id *id)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc;
>> +	int ret;
>> +
>> +	ssif_bmc = devm_kzalloc(&client->dev, sizeof(*ssif_bmc), GFP_KERNEL);
>> +	if (!ssif_bmc)
>> +		return -ENOMEM;
>> +
>> +	spin_lock_init(&ssif_bmc->lock);
>> +
>> +	init_waitqueue_head(&ssif_bmc->wait_queue);
>> +	ssif_bmc->request_available = false;
>> +	ssif_bmc->response_in_progress = false;
>> +	ssif_bmc->busy = false;
>> +	ssif_bmc->response_timer_inited = false;
>> +
>> +	/* Register misc device interface */
>> +	ssif_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
>> +	ssif_bmc->miscdev.name = DEVICE_NAME;
>> +	ssif_bmc->miscdev.fops = &ssif_bmc_fops;
>> +	ssif_bmc->miscdev.parent = &client->dev;
>> +	ret = misc_register(&ssif_bmc->miscdev);
>> +	if (ret)
>> +		goto out;
>> +
>> +	ssif_bmc->client = client;
>> +	ssif_bmc->client->flags |= I2C_CLIENT_SLAVE;
>> +
>> +	/* Register I2C slave */
>> +	i2c_set_clientdata(client, ssif_bmc);
>> +	ret = i2c_slave_register(client, ssif_bmc_cb);
>> +	if (ret) {
>> +		misc_deregister(&ssif_bmc->miscdev);
>> +		goto out;
>> +	}
>> +
>> +	return 0;
>> +out:
>> +	devm_kfree(&client->dev, ssif_bmc);
>> +	return ret;
>> +}
>> +
>> +static int ssif_bmc_remove(struct i2c_client *client)
>> +{
>> +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
>> +
>> +	i2c_slave_unregister(client);
>> +	misc_deregister(&ssif_bmc->miscdev);
>> +
>> +	return 0;
>> +}
>> +
>> +static const struct of_device_id ssif_bmc_match[] = {
>> +	{ .compatible = "ampere,ssif-bmc" },
>> +	{ },
>> +};
>> +
>> +static const struct i2c_device_id ssif_bmc_id[] = {
>> +	{ DEVICE_NAME, 0 },
>> +	{ },
>> +};
>> +
>> +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
>> +
>> +static struct i2c_driver ssif_bmc_driver = {
>> +	.driver         = {
>> +		.name           = DEVICE_NAME,
>> +		.of_match_table = ssif_bmc_match,
>> +	},
>> +	.probe          = ssif_bmc_probe,
>> +	.remove         = ssif_bmc_remove,
>> +	.id_table       = ssif_bmc_id,
>> +};
>> +
>> +module_i2c_driver(ssif_bmc_driver);
>> +
>> +MODULE_AUTHOR("Quan Nguyen <[e-mail]>");
>> +MODULE_AUTHOR("Chuong Tran <[e-mail]>");
>> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF interface.");
>> +MODULE_LICENSE("GPL");
>> diff --git a/drivers/char/ipmi/ssif_bmc.h b/drivers/char/ipmi/ssif_bmc.h
>> new file mode 100644
>> index 000000000000..9a26f3c252cc
>> --- /dev/null
>> +++ b/drivers/char/ipmi/ssif_bmc.h
>> @@ -0,0 +1,102 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +/*
>> + * The driver for BMC side of SSIF interface
>> + *
>> + * Copyright (c) 2022, Ampere Computing LLC
>> + *
>> + */
>> +#ifndef __SSIF_BMC_H__
>> +#define __SSIF_BMC_H__
>> +
>> +#define DEVICE_NAME				"ipmi-ssif-host"
>> +
>> +#define GET_8BIT_ADDR(addr_7bit)		(((addr_7bit) << 1) & 0xff)
>> +
>> +/* A standard SMBus Transaction is limited to 32 data bytes */
>> +#define MAX_PAYLOAD_PER_TRANSACTION		32
>> +
>> +#define MAX_IPMI_DATA_PER_START_TRANSACTION	30
>> +#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION	31
>> +
>> +#define SSIF_IPMI_SINGLEPART_WRITE		0x2
>> +#define SSIF_IPMI_SINGLEPART_READ		0x3
>> +#define SSIF_IPMI_MULTIPART_WRITE_START		0x6
>> +#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE	0x7
>> +#define SSIF_IPMI_MULTIPART_WRITE_END		0x8
>> +#define SSIF_IPMI_MULTIPART_READ_START		0x3
>> +#define SSIF_IPMI_MULTIPART_READ_MIDDLE		0x9
>> +
>> +#define MSG_PAYLOAD_LEN_MAX			252
>> +/*
>> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
>> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
>> + * Recover ssif_bmc from busy state if it takes upto 500ms
>> + */
>> +#define RESPONSE_TIMEOUT			500 /* ms */
>> +
>> +struct ssif_msg {
>> +	u8 len;
>> +	u8 netfn_lun;
>> +	u8 cmd;
>> +	u8 payload[MSG_PAYLOAD_LEN_MAX];
>> +} __packed;
>> +
>> +static inline u32 ssif_msg_len(struct ssif_msg *ssif_msg)
>> +{
>> +	return ssif_msg->len + 1;
>> +}
>> +
>> +/*
>> + * SSIF internal states:
>> + *   SSIF_READY         0x00 : Ready state
>> + *   SSIF_START         0x01 : Start smbus transaction
>> + *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
>> + *   SSIF_REQ_RECVING   0x03 : Receiving request
>> + *   SSIF_RES_SENDING   0x04 : Sending response
>> + *   SSIF_BAD_SMBUS     0x05 : Bad SMbus transaction
>> + */
>> +enum ssif_state {
>> +	SSIF_READY,
>> +	SSIF_START,
>> +	SSIF_SMBUS_CMD,
>> +	SSIF_REQ_RECVING,
>> +	SSIF_RES_SENDING,
>> +	SSIF_BAD_SMBUS,
>> +	SSIF_STATE_MAX
>> +};
>> +
>> +struct ssif_bmc_ctx {
>> +	struct i2c_client	*client;
>> +	struct miscdevice	miscdev;
>> +	size_t			msg_idx;
>> +	bool			pec_support;
>> +	/* ssif bmc spinlock */
>> +	spinlock_t		lock;
>> +	wait_queue_head_t	wait_queue;
>> +	u8			running;
>> +	enum ssif_state		state;
>> +	u8			smbus_cmd;
>> +	/* Timeout waiting for response */
>> +	struct timer_list	response_timer;
>> +	bool                    response_timer_inited;
>> +	/* Flag to identify a Multi-part Read Transaction */
>> +	bool			is_singlepart_read;
>> +	u8			nbytes_processed;
>> +	u8			remain_len;
>> +	u8			recv_len;
>> +	/* Block Number of a Multi-part Read Transaction */
>> +	u8			block_num;
>> +	bool			request_available;
>> +	bool			response_in_progress;
>> +	bool			busy;
>> +	/* Response buffer for Multi-part Read Transaction */
>> +	u8			response_buf[MAX_PAYLOAD_PER_TRANSACTION];
>> +	struct ssif_msg		response;
>> +	struct ssif_msg		request;
>> +};
>> +
>> +static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
>> +{
>> +	return container_of(file->private_data, struct ssif_bmc_ctx, miscdev);
>> +}
>> +#endif /* __SSIF_BMC_H__ */
>> -- 
>> 2.35.1
>>
>>

Quan Nguyen March 17, 2022, 9 a.m. UTC | #5

On 15/03/2022 01:15, Jae Hyun Yoo wrote:
> Hi Quan,
> 
> [...]
> 
>> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY ||
>> +        ssif_bmc->state == SSIF_START ||
>> +        ssif_bmc->state == SSIF_REQ_RECVING ||
>> +        ssif_bmc->state == SSIF_RES_SENDING) {
>> +        ssif_bmc->state = SSIF_BAD_SMBUS;
>> +        dev_warn(&ssif_bmc->client->dev,
>> +             "Warn: %s unexpected READ REQUESTED in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
> 
> It will print out that the case happens in SSIF_BAD_SMBUS state always
> because ssif_bmc->state is already assigned as SSIF_BAD_SMBUS above.
> Move the assignment to after the dev_warn printing.
> 
> [...]
> 

Thanks for pointing this out. Will fix this in next version.

>> +static const struct of_device_id ssif_bmc_match[] = {
>> +    { .compatible = "ampere,ssif-bmc" },
> 
> Does this driver have any Ampere specific handling? If not, it could be
> "ssif-bmc" as a generic SSIF driver.
> 
Will change as you suggested in next version.

>> +    { },
>> +};
> 
> Add 'MODULE_DEVICE_TABLE(of, ssif_bmc_match);'
> 
Will do in next version
>> +
>> +static const struct i2c_device_id ssif_bmc_id[] = {
>> +    { DEVICE_NAME, 0 },
>> +    { },
>> +};
>> +
> 
> Remove this blank line.
> 
Will update in next version

>> +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
>> +
>> +static struct i2c_driver ssif_bmc_driver = {
>> +    .driver         = {
>> +        .name           = DEVICE_NAME,
>> +        .of_match_table = ssif_bmc_match,
>> +    },
>> +    .probe          = ssif_bmc_probe,
>> +    .remove         = ssif_bmc_remove,
>> +    .id_table       = ssif_bmc_id,
>> +};
>> +
> 
> Remove this blank line too.
> 
> -Jae
>

Thanks Jae for the review, will update in next version.
- Quan

>> +module_i2c_driver(ssif_bmc_driver);
>> +
>> +MODULE_AUTHOR("Quan Nguyen <[e-mail]>");
>> +MODULE_AUTHOR("Chuong Tran <[e-mail]>");
>> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF 
>> interface.");
>> +MODULE_LICENSE("GPL");
> 
> [...]

Corey Minyard March 17, 2022, 1:13 p.m. UTC | #6

snip...
> > > +
> > > +static void response_timeout(struct timer_list *t)
> > > +{
> > > +	struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, response_timer);
> > > +	unsigned long flags;
> > > +
> > 
> > Is there a possible race here?  The timeout can happen at the same time
> > as a received message, will something bad happen if that's the case?
> > 
> 
> Thanks Corey,
> I think I need extra comment here.
> 
> The purpose of this timeout is to make sure ssif_bmc will recover from busy
> state in case the upper stack does not provide the response.
> Hence, the response timeout is set as 500ms, twice the time of max
> Request-to-Response in spec as the code below. Should it be longer?

That's not what I was asking.  I know what the timer is for.  But what
happens if the response comes in at the same time this timer goes off?
What will keep the data from getting messed up?

> 
> As per spec, the max Request-to-Respose would not exceed 250ms.
> 
> I put the comment in ssif_bmc.h as below:
> >> +/*
> >> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
> >> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
> >> + * Recover ssif_bmc from busy state if it takes upto 500ms
> >> + */
> >> +#define RESPONSE_TIMEOUT			500 /* ms */
> 
> 
> > > +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> > > +
> > > +	/* Recover ssif_bmc from busy */
> > > +	ssif_bmc->busy = false;
> > > +	del_timer(&ssif_bmc->response_timer);
> > 
> > You don't need to delete the timer, it's in the timeout.
> > 
> 
> Will remove this redundant code in next version
> 
> > > +	ssif_bmc->response_timer_inited = false;
> > > +
> > > +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> > > +}
> > > +
> > > +/* Called with ssif_bmc->lock held. */
> > > +static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
> > > +{
> > > +	/* set ssif_bmc to busy waiting for response */
> > > +	ssif_bmc->busy = true;
> > > +
> > > +	/* Request message is available to process */
> > > +	ssif_bmc->request_available = true;
> > > +
> > > +	/* Clean old response buffer */
> > > +	memset(&ssif_bmc->response, 0, sizeof(struct ssif_msg));
> > > +
> > > +	/* This is the new READ request.*/
> > > +	wake_up_all(&ssif_bmc->wait_queue);
> > > +
> > > +	/* Armed timer to recover slave from busy state in case of no response */
> > > +	if (!ssif_bmc->response_timer_inited) {
> > > +		timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
> > > +		ssif_bmc->response_timer_inited = true;
> > > +	}
> > > +	mod_timer(&ssif_bmc->response_timer, jiffies + msecs_to_jiffies(RESPONSE_TIMEOUT));
> > > +}
> > > +
> > > +static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	u8 response_len = 0;
> > > +	int idx = 0;
> > > +	u8 data_len;
> > > +
> > > +	data_len = ssif_bmc->response.len;
> > > +	switch (ssif_bmc->smbus_cmd) {
> > > +	case SSIF_IPMI_MULTIPART_READ_START:
> > > +		/*
> > > +		 * Read Start length is 32 bytes.
> > > +		 * Read Start transfer first 30 bytes of IPMI response
> > > +		 * and 2 special code 0x00, 0x01.
> > > +		 */
> > > +		*val = MAX_PAYLOAD_PER_TRANSACTION;
> > > +		ssif_bmc->remain_len = data_len - MAX_IPMI_DATA_PER_START_TRANSACTION;
> > > +		ssif_bmc->block_num = 0;
> > 
> > Do you need to validate the data length before using this?
> > This applies for lots of places through here.
> > 
> 
> set_multipart_response_buffer() is called only when ->is_singlepart_read is
> false, which is determined by the below code under the *_write()
> 
> ssif_bmc->is_singlepart_read = (ssif_msg_len(&msg) <=
> MAX_PAYLOAD_PER_TRANSACTION + 1);
> 
> So, I think the len is validated and could be use in this functions.

Ah, I had things backwards.  "Read" here is when you are writing to
the other side.  I understand now.

> 
> > > +
> > > +		ssif_bmc->response_buf[idx++] = 0x00; /* Start Flag */
> > > +		ssif_bmc->response_buf[idx++] = 0x01; /* Start Flag */
> > > +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.netfn_lun;
> > > +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.cmd;
> > > +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.payload[0];
> > > +
> > > +		response_len = MAX_PAYLOAD_PER_TRANSACTION - idx;
> > > +
> > > +		memcpy(&ssif_bmc->response_buf[idx], &ssif_bmc->response.payload[1],
> > > +		       response_len);
> > > +		break;
> > > +
> > > +	case SSIF_IPMI_MULTIPART_READ_MIDDLE:
> > > +		/*
> > > +		 * IPMI READ Middle or READ End messages can carry up to 31 bytes
> > > +		 * IPMI data plus block number byte.
> > > +		 */
> > > +		if (ssif_bmc->remain_len < MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
> > > +			/*
> > > +			 * This is READ End message
> > > +			 *  Return length is the remaining response data length
> > > +			 *  plus block number
> > > +			 *  Block number 0xFF is to indicate this is last message
> > > +			 *
> > > +			 */
> > > +			*val = ssif_bmc->remain_len + 1;
> > > +			ssif_bmc->block_num = 0xFF;
> > > +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
> > > +			response_len = ssif_bmc->remain_len;
> > > +			/* Clean the buffer */
> > > +			memset(&ssif_bmc->response_buf[idx], 0, MAX_PAYLOAD_PER_TRANSACTION - idx);
> > > +		} else {
> > > +			/*
> > > +			 * This is READ Middle message
> > > +			 *  Response length is the maximum SMBUS transfer length
> > > +			 *  Block number byte is incremented
> > > +			 * Return length is maximum SMBUS transfer length
> > > +			 */
> > > +			*val = MAX_PAYLOAD_PER_TRANSACTION;
> > > +			ssif_bmc->remain_len -= MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
> > > +			response_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
> > > +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
> > > +			ssif_bmc->block_num++;
> > > +		}
> > > +
> > > +		memcpy(&ssif_bmc->response_buf[idx],
> > > +		       ssif_bmc->response.payload + 1 + ssif_bmc->nbytes_processed,
> > > +		       response_len);
> > > +		break;
> > > +
> > > +	default:
> > > +		/* Do not expect to go to this case */
> > > +		dev_err(&ssif_bmc->client->dev,
> > > +			"%s: Unexpected SMBus command 0x%x\n",
> > > +			__func__, ssif_bmc->smbus_cmd);
> > > +		break;
> > > +	}
> > > +
> > > +	ssif_bmc->nbytes_processed += response_len;
> > > +}
> > > +
> > > +/* Process the IPMI response that will be read by master */
> > > +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	u8 *buf;
> > > +	u8 pec_len, addr, len;
> > > +	u8 pec = 0;
> > > +
> > > +	pec_len = ssif_bmc->pec_support ? 1 : 0;
> > > +	/* PEC - Start Read Address */
> > > +	addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
> > > +	pec = i2c_smbus_pec(pec, &addr, 1);
> > > +	/* PEC - SSIF Command */
> > > +	pec = i2c_smbus_pec(pec, &ssif_bmc->smbus_cmd, 1);
> > > +	/* PEC - Restart Write Address */
> > > +	addr = addr | 0x01;
> > > +	pec = i2c_smbus_pec(pec, &addr, 1);
> > > +
> > > +	if (ssif_bmc->is_singlepart_read) {
> > > +		/* Single-part Read processing */
> > > +		buf = (u8 *)&ssif_bmc->response;
> > > +
> > > +		if (ssif_bmc->response.len && ssif_bmc->msg_idx < ssif_bmc->response.len) {
> > > +			ssif_bmc->msg_idx++;
> > > +			*val = buf[ssif_bmc->msg_idx];
> > > +		} else if (ssif_bmc->response.len && ssif_bmc->msg_idx == ssif_bmc->response.len) {
> > > +			ssif_bmc->msg_idx++;
> > > +			*val = i2c_smbus_pec(pec, buf, ssif_msg_len(&ssif_bmc->response));
> > > +		} else {
> > 
> > I thought for a second that this was wrong, but I think it's correct.
> > Supply zero if you don't have data.
> > 
> > > +			*val = 0;
> > > +		}
> > > +		/* Invalidate response buffer to denote it is sent */
> > > +		if (ssif_bmc->msg_idx + 1 >= (ssif_msg_len(&ssif_bmc->response) + pec_len))
> > > +			complete_response(ssif_bmc);
> > > +	} else {
> > > +		/* Multi-part Read processing */
> > 
> > You don't check the length here like you did above.  I think that's
> > required.
> > 
> 
> As per my explanation above, the ->is_singlepart_read is determined by
> testing the length, so it is validated as I assumed.
> 
> > > +		switch (ssif_bmc->smbus_cmd) {
> > > +		case SSIF_IPMI_MULTIPART_READ_START:
> > > +		case SSIF_IPMI_MULTIPART_READ_MIDDLE:
> > > +			buf = (u8 *)&ssif_bmc->response_buf;
> > > +			*val = buf[ssif_bmc->msg_idx];
> > > +			ssif_bmc->msg_idx++;
> > > +			break;
> > > +		default:
> > > +			/* Do not expect to go to this case */
> > > +			dev_err(&ssif_bmc->client->dev,
> > > +				"%s: Unexpected SMBus command 0x%x\n",
> > > +				__func__, ssif_bmc->smbus_cmd);
> > > +			break;
> > > +		}
> > > +
> > > +		len = (ssif_bmc->block_num == 0xFF) ?
> > > +		       ssif_bmc->remain_len + 1 : MAX_PAYLOAD_PER_TRANSACTION;
> > > +		if (ssif_bmc->msg_idx == (len + 1)) {
> > > +			pec = i2c_smbus_pec(pec, &len, 1);
> > > +			*val = i2c_smbus_pec(pec, ssif_bmc->response_buf, len);
> > > +		}
> > > +		/* Invalidate response buffer to denote last response is sent */
> > > +		if (ssif_bmc->block_num == 0xFF &&
> > > +		    ssif_bmc->msg_idx > (ssif_bmc->remain_len + pec_len)) {
> > > +			complete_response(ssif_bmc);
> > > +		}
> > > +	}
> > > +}
> > > +
> > > +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	u8 *buf = (u8 *)&ssif_bmc->request;
> > > +
> > > +	if (ssif_bmc->msg_idx >= sizeof(struct ssif_msg))
> > > +		return;

I don't think this check is valid.  I believe the msg_idx only covers
the current message, but ssif_msg is a full multi-part message.  It
covers the single-part message, I think but not the multi-part ones.
Also, abort the operation and log on bad data.

> > > +
> > > +	switch (ssif_bmc->smbus_cmd) {
> > > +	case SSIF_IPMI_SINGLEPART_WRITE:
> > > +		buf[ssif_bmc->msg_idx - 1] = *val;
> > > +		ssif_bmc->msg_idx++;
> > > +
> > > +		break;
> > > +	case SSIF_IPMI_MULTIPART_WRITE_START:
> > > +		if (ssif_bmc->msg_idx == 1)
> > > +			ssif_bmc->request.len = 0;
> > > +
> > > +		fallthrough;
> > > +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
> > > +		/* The len should always be 32 */
> > > +		if (ssif_bmc->msg_idx == 1 && *val != MAX_PAYLOAD_PER_TRANSACTION)
> > > +			dev_warn(&ssif_bmc->client->dev,
> > > +				 "Warn: Invalid Multipart Write len");

You should abort the operation here.  Don't deliver obviously bad data.
Same in the code just below.

This will require that you add a message aborted type of state to just
ignore everything that comes in until the full sequence ends or a new
message starts.

> > > +
> > > +		fallthrough;
> > > +	case SSIF_IPMI_MULTIPART_WRITE_END:
> > > +		/* Multi-part write, 2nd byte received is length */
> > > +		if (ssif_bmc->msg_idx == 1) {
> > > +			if (*val > MAX_PAYLOAD_PER_TRANSACTION)
> > > +				dev_warn(&ssif_bmc->client->dev,
> > > +					 "Warn: Invalid Multipart Write End len");
> > > +
> > > +			ssif_bmc->request.len += *val;
> > > +			ssif_bmc->recv_len = *val;
> > > +
> > > +			/* request len should never exceeded 255 bytes */
> > > +			if (ssif_bmc->request.len > 255)
> > > +				dev_warn(&ssif_bmc->client->dev,
> > > +					 "Warn: Invalid request len");
> > > +
> > > +		} else {
> > 
> > You check msg_idx above, but I'm not sure that check will cover this
> > operation.
> > 
> That check is to make sure the length (*val) must always be strictly 32
> bytes in case of MULTIPART_WRITE_START/MIDDLE. And this check allows the
> length is up to 32 bytes in MULTIPART_WRITE_END.

Now that I have read and write straight, this is where the previous
comments apply.

You are trusting the the length sent by the remote end in the second
byte is correct, but there is no guarantee of this.  The remote end can
send as many bytes as it likes.  You need to check that you don't
overflow buf here and that it actually sends the number of bytes that it
said it was going to send to avoid underflow.

> 
> > > +			buf[ssif_bmc->msg_idx - 1 +
> > > +			    ssif_bmc->request.len - ssif_bmc->recv_len]	= *val;

This computation is fairly complicated and hard to understand.
Calculations like this are asking for trouble.

It would be easier to understand had request.len be the current length
of what is in request.payload and increment it on every incoming byte.
Then request.len could be used to add data to the buffer, like

	if (ssif_bmc->request.len >= sizeof(ssif_bmc->payload))
		error...
	ssif_bmc->payload[ssif_bmc->request.len++] = *val;

If you renamed msg_idx to curr_recv_idx and recv_len to curr_recv_len,
it would be more clear that these are related and operate on the current
incoming message.

It would also be nice to get rid of the casts from ssif_msg to a buffer
array and just index directly into request.payload[].

In thinking about this further, I have a few more observations...

There is no need to have the netfn and cmd in ssif_msg.  They are just
the first and second bytes of the message.  You don't care what they
are in this code.

Why do you deliver the length as part of the message to the user?  The
length is returned by the system call.  You have all these +1 and -1
things around the message length, which is error-prone.  Removing the
length from the message would get rid of all of that.  And using packed
structures is generally not the best, anyway.

The PEC calculations remove one byte from the maximum message length.
Since they are not included in the length byte, it's kind of unnatural
to do this the way you are doing it.  Instead, it might be best to say
if you receive a byte and curr_recv_idx == curr_recv_len, process it
as PEC.  That way the PEC never hits the buffer.

There is no need for msg_idx, or cur_recv_idx, to be size_t.

I need to look at this some more, but I'll need to see the rewrite.

-corey

> > > +		}
> > > +
> > > +		ssif_bmc->msg_idx++;
> > > +
> > > +		break;
> > > +	default:
> > > +		/* Do not expect to go to this case */
> > > +		dev_err(&ssif_bmc->client->dev,
> > > +			"%s: Unexpected SMBus command 0x%x\n",
> > > +			__func__, ssif_bmc->smbus_cmd);
> > > +		break;
> > > +	}
> > > +}
> > > +
> > > +static bool validate_request(struct ssif_bmc_ctx *ssif_bmc)
> > > +{
> > > +	u8 rpec = 0, cpec = 0;
> > > +	bool ret = true;
> > > +	u8 addr, index;
> > > +	u8 *buf;
> > > +
> > 
> > Is there any length validation for using buf below?  It looks like you
> > are accessing without checking length, but maybe I missed something.
> > 
> 
> Yes, there is length testing for each part before using buf to calculate PEC
> as in the "if" below.
> 
> > > +	buf = (u8 *)&ssif_bmc->request;
> > > +	switch (ssif_bmc->smbus_cmd) {
> > > +	case SSIF_IPMI_SINGLEPART_WRITE:
> > > +		if ((ssif_bmc->msg_idx - 1) == ssif_msg_len(&ssif_bmc->request)) {
> > > +			/* PEC is not included */
> > > +			ssif_bmc->pec_support = false;
> > > +			ret = true;
> > > +			goto exit;
> > > +		}
> > > +
> > > +		if ((ssif_bmc->msg_idx - 1) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
> > > +			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
> > > +				ssif_msg_len(&ssif_bmc->request));
> > > +			ret = false;
> > > +			goto exit;
> > > +		}
> > > +
> > > +		/* PEC is included */
> > > +		ssif_bmc->pec_support = true;
> > > +		rpec = buf[ssif_bmc->msg_idx - 2];
> > > +		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
> > > +		cpec = i2c_smbus_pec(cpec, &addr, 1);
> > > +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
> > > +		cpec = i2c_smbus_pec(cpec, buf, ssif_msg_len(&ssif_bmc->request));
> > > +		if (rpec != cpec) {
> > > +			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
> > > +			ret = false;
> > > +		}
> > > +
> > > +		break;
> > > +	case SSIF_IPMI_MULTIPART_WRITE_START:
> > > +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
> > > +	case SSIF_IPMI_MULTIPART_WRITE_END:
> > > +		index = ssif_bmc->request.len - ssif_bmc->recv_len;
> > > +		if ((ssif_bmc->msg_idx - 1 + index) == ssif_msg_len(&ssif_bmc->request)) {
> > > +			/* PEC is not included */
> > > +			ssif_bmc->pec_support = false;
> > > +			ret = true;
> > > +			goto exit;
> > > +		}
> > > +
> > > +		if ((ssif_bmc->msg_idx - 1 + index) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
> > > +			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
> > > +				ssif_msg_len(&ssif_bmc->request));
> > > +			ret = false;
> > > +			goto exit;
> > > +		}
> > > +
> > > +		/* PEC is included */
> > > +		ssif_bmc->pec_support = true;
> > > +		rpec = buf[ssif_bmc->msg_idx - 2 + index];
> > > +		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
> > > +		cpec = i2c_smbus_pec(cpec, &addr, 1);
> > > +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
> > > +		cpec = i2c_smbus_pec(cpec, &ssif_bmc->recv_len, 1);
> > 
> > Just curious, I'm not sure the client side PEC in the Linux driver has
> > ever been validated.  Have you tested both sides?
> > 
> 
> Yes, we found that request from host has an extra byte for PEC and that is
> why we added PEC support.
> 
> > > +		/* As SMBus specification does not allow the length
> > > +		 * (byte count) in the Write-Block protocol to be zero.
> > > +		 * Therefore, it is illegal to have the last Middle
> > > +		 * transaction in the sequence carry 32-byte and have
> > > +		 * a length of ‘0’ in the End transaction.
> > > +		 * But some users may try to use this way and we should
> > > +		 * prevent ssif_bmc driver broken in this case.
> > > +		 */
> > > +		if (ssif_bmc->recv_len != 0)
> > > +			cpec = i2c_smbus_pec(cpec, buf + 1 + index, ssif_bmc->recv_len);
> > > +
> > > +		if (rpec != cpec) {
> > > +			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
> > > +			ret = false;
> > > +		}
> > > +
> > > +		break;
> > > +	default:
> > > +		/* Do not expect to go to this case */
> > > +		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 0x%x\n",
> > > +			__func__, ssif_bmc->smbus_cmd);
> > > +		ret = false;
> > > +		break;
> > > +	}
> > > +
> > > +exit:
> > > +	return ret;
> > > +}
> > > +
> > 
> > Just a nit, more a general coding style comment.  It's almost always a
> > bad idea to put a negative (unsupported) into a check function.  You
> > often end up with something like:
> > 
> > 	if (!unsupported_smbus_cmd(c))....
> > 
> > which looks a little strange.  Double negatives can make it hard to
> > follow and lead to mistakes.  This one isn't too bad, but sometimes it
> > can be.  It's better to do:
> > 
> > 	if (supported_smbus_cmd(c))....
> > or
> > 	if (!supported_smbus_cmd(c))....
> > 
> > 
> 
> Thanks, Corey. I'll try to refactor this part in next version.
> 
> > > +static bool unsupported_smbus_cmd(u8 cmd)
> > > +{
> > > +	if (cmd == SSIF_IPMI_SINGLEPART_READ ||
> > > +	    cmd == SSIF_IPMI_SINGLEPART_WRITE ||
> > > +	    cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
> > > +	    cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
> > > +	    cmd == SSIF_IPMI_MULTIPART_WRITE_END ||
> > > +	    cmd == SSIF_IPMI_MULTIPART_READ_START ||
> > > +	    cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
> > > +		return false;
> > > +
> > > +	return true;
> > > +}
> > > +
> > > +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	/* SMBUS command can vary (single or multi-part) */
> > > +	ssif_bmc->smbus_cmd = *val;
> > > +	ssif_bmc->msg_idx++;
> > > +
> > > +	if (unsupported_smbus_cmd(*val))
> > > +		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus command");
> > > +
> > > +	if (*val == SSIF_IPMI_SINGLEPART_WRITE ||
> > > +	    *val == SSIF_IPMI_MULTIPART_WRITE_START) {
> > > +		/*
> > > +		 * The response maybe not come in-time, causing host SSIF driver
> > > +		 * to timeout and resend a new request. In such case check for
> > > +		 * pending response and clear it
> > > +		 */
> > > +		if (ssif_bmc->response_in_progress)
> > > +			complete_response(ssif_bmc);
> > > +	}
> > > +}
> > > +
> > > +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	if (ssif_bmc->state == SSIF_READY ||
> > > +	    ssif_bmc->state == SSIF_START ||
> > > +	    ssif_bmc->state == SSIF_REQ_RECVING ||
> > > +	    ssif_bmc->state == SSIF_RES_SENDING) {
> > > +		ssif_bmc->state = SSIF_BAD_SMBUS;
> > > +		dev_warn(&ssif_bmc->client->dev,
> > > +			 "Warn: %s unexpected READ REQUESTED in state=%s\n",
> > > +			 __func__, state_to_string(ssif_bmc->state));
> > > +
> > > +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
> > > +		ssif_bmc->state = SSIF_RES_SENDING;
> > > +	}
> > > +
> > > +	ssif_bmc->msg_idx = 0;
> > > +	if (ssif_bmc->is_singlepart_read)
> > > +		*val = ssif_bmc->response.len;
> > > +	else
> > > +		set_multipart_response_buffer(ssif_bmc, val);
> > > +}
> > > +
> > > +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	if (ssif_bmc->state == SSIF_READY ||
> > > +	    ssif_bmc->state == SSIF_START ||
> > > +	    ssif_bmc->state == SSIF_REQ_RECVING ||
> > > +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
> > > +		dev_warn(&ssif_bmc->client->dev,
> > > +			 "Warn: %s unexpected READ PROCESSED in state=%s\n",
> > > +			 __func__, state_to_string(ssif_bmc->state));
> > > +		ssif_bmc->state = SSIF_BAD_SMBUS;
> > > +	}
> > > +
> > > +	handle_read_processed(ssif_bmc, val);
> > > +}
> > > +
> > > +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	ssif_bmc->msg_idx = 0;
> > > +
> > > +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_SMBUS_CMD) {
> > > +		ssif_bmc->state = SSIF_START;
> > > +
> > > +	} else if (ssif_bmc->state == SSIF_START ||
> > > +		   ssif_bmc->state == SSIF_REQ_RECVING ||
> > > +		   ssif_bmc->state == SSIF_RES_SENDING) {
> > > +		dev_warn(&ssif_bmc->client->dev,
> > > +			 "Warn: %s unexpected WRITE REQUEST in state=%s\n",
> > > +			 __func__, state_to_string(ssif_bmc->state));
> > > +		ssif_bmc->state = SSIF_BAD_SMBUS;
> > > +	}
> > > +}
> > > +
> > > +static void on_write_received_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_RES_SENDING) {
> > > +		dev_warn(&ssif_bmc->client->dev,
> > > +			 "Warn: %s unexpected WRITE RECEIVED in state=%s\n",
> > > +			 __func__, state_to_string(ssif_bmc->state));
> > > +		ssif_bmc->state = SSIF_BAD_SMBUS;
> > > +	} else if (ssif_bmc->state == SSIF_START) {
> > > +		ssif_bmc->state = SSIF_SMBUS_CMD;
> > > +	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
> > > +		ssif_bmc->state = SSIF_REQ_RECVING;
> > > +	}
> > > +
> > > +	/* This is response sending state */
> > > +	if (ssif_bmc->state == SSIF_REQ_RECVING)
> > > +		handle_write_received(ssif_bmc, val);
> > > +	else if (ssif_bmc->state == SSIF_SMBUS_CMD)
> > > +		process_smbus_cmd(ssif_bmc, val);
> > > +}
> > > +
> > > +static void on_stop_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
> > > +{
> > > +	if (ssif_bmc->state == SSIF_READY ||
> > > +	    ssif_bmc->state == SSIF_START ||
> > > +	    ssif_bmc->state == SSIF_SMBUS_CMD) {
> > > +		dev_warn(&ssif_bmc->client->dev,
> > > +			 "Warn: %s unexpected SLAVE STOP in state=%s\n",
> > > +			 __func__, state_to_string(ssif_bmc->state));
> > > +
> > > +	} else if (ssif_bmc->state == SSIF_BAD_SMBUS) {
> > > +		dev_warn(&ssif_bmc->client->dev,
> > > +			 "Warn: %s received SLAVE STOP from bad state=%s\n",
> > > +			 __func__, state_to_string(ssif_bmc->state));
> > > +
> > > +	} else if (ssif_bmc->state == SSIF_REQ_RECVING) {
> > > +		/* A BMC that receives an invalid request drop the data for the write
> > > +		 * transaction and any further transactions (read or write) until
> > > +		 * the next valid read or write Start transaction is received
> > > +		 */
> > > +		if (!validate_request(ssif_bmc))
> > > +			dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
> > > +		else if (ssif_bmc->smbus_cmd == SSIF_IPMI_SINGLEPART_WRITE ||
> > > +			 ssif_bmc->smbus_cmd == SSIF_IPMI_MULTIPART_WRITE_END)
> > > +			handle_request(ssif_bmc);
> > > +	}
> > > +
> > > +	ssif_bmc->state = SSIF_READY;
> > > +	/* Reset message index */
> > > +	ssif_bmc->msg_idx = 0;
> > > +}
> > > +
> > > +/*
> > > + * Callback function to handle I2C slave events
> > > + */
> > > +static int ssif_bmc_cb(struct i2c_client *client, enum i2c_slave_event event, u8 *val)
> > > +{
> > > +	unsigned long flags;
> > > +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
> > > +	int ret = 0;
> > > +
> > > +	spin_lock_irqsave(&ssif_bmc->lock, flags);
> > > +
> > > +	switch (event) {
> > > +	case I2C_SLAVE_READ_REQUESTED:
> > > +		on_read_requested_event(ssif_bmc, val);
> > > +		break;
> > > +
> > > +	case I2C_SLAVE_WRITE_REQUESTED:
> > > +		on_write_requested_event(ssif_bmc, val);
> > > +		break;
> > > +
> > > +	case I2C_SLAVE_READ_PROCESSED:
> > > +		on_read_processed_event(ssif_bmc, val);
> > > +		break;
> > > +
> > > +	case I2C_SLAVE_WRITE_RECEIVED:
> > > +		on_write_received_event(ssif_bmc, val);
> > > +		break;
> > > +
> > > +	case I2C_SLAVE_STOP:
> > > +		on_stop_event(ssif_bmc, val);
> > > +		break;
> > > +
> > > +	default:
> > > +		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown i2c slave event\n");
> > > +		break;
> > > +	}
> > > +
> > > +	if (ssif_bmc->busy)
> > > +		ret = -EBUSY;
> > > +
> > > +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
> > > +
> > > +	return ret;
> > > +}
> > > +
> > > +static int ssif_bmc_probe(struct i2c_client *client, const struct i2c_device_id *id)
> > > +{
> > > +	struct ssif_bmc_ctx *ssif_bmc;
> > > +	int ret;
> > > +
> > > +	ssif_bmc = devm_kzalloc(&client->dev, sizeof(*ssif_bmc), GFP_KERNEL);
> > > +	if (!ssif_bmc)
> > > +		return -ENOMEM;
> > > +
> > > +	spin_lock_init(&ssif_bmc->lock);
> > > +
> > > +	init_waitqueue_head(&ssif_bmc->wait_queue);
> > > +	ssif_bmc->request_available = false;
> > > +	ssif_bmc->response_in_progress = false;
> > > +	ssif_bmc->busy = false;
> > > +	ssif_bmc->response_timer_inited = false;
> > > +
> > > +	/* Register misc device interface */
> > > +	ssif_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
> > > +	ssif_bmc->miscdev.name = DEVICE_NAME;
> > > +	ssif_bmc->miscdev.fops = &ssif_bmc_fops;
> > > +	ssif_bmc->miscdev.parent = &client->dev;
> > > +	ret = misc_register(&ssif_bmc->miscdev);
> > > +	if (ret)
> > > +		goto out;
> > > +
> > > +	ssif_bmc->client = client;
> > > +	ssif_bmc->client->flags |= I2C_CLIENT_SLAVE;
> > > +
> > > +	/* Register I2C slave */
> > > +	i2c_set_clientdata(client, ssif_bmc);
> > > +	ret = i2c_slave_register(client, ssif_bmc_cb);
> > > +	if (ret) {
> > > +		misc_deregister(&ssif_bmc->miscdev);
> > > +		goto out;
> > > +	}
> > > +
> > > +	return 0;
> > > +out:
> > > +	devm_kfree(&client->dev, ssif_bmc);
> > > +	return ret;
> > > +}
> > > +
> > > +static int ssif_bmc_remove(struct i2c_client *client)
> > > +{
> > > +	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
> > > +
> > > +	i2c_slave_unregister(client);
> > > +	misc_deregister(&ssif_bmc->miscdev);
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +static const struct of_device_id ssif_bmc_match[] = {
> > > +	{ .compatible = "ampere,ssif-bmc" },
> > > +	{ },
> > > +};
> > > +
> > > +static const struct i2c_device_id ssif_bmc_id[] = {
> > > +	{ DEVICE_NAME, 0 },
> > > +	{ },
> > > +};
> > > +
> > > +MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
> > > +
> > > +static struct i2c_driver ssif_bmc_driver = {
> > > +	.driver         = {
> > > +		.name           = DEVICE_NAME,
> > > +		.of_match_table = ssif_bmc_match,
> > > +	},
> > > +	.probe          = ssif_bmc_probe,
> > > +	.remove         = ssif_bmc_remove,
> > > +	.id_table       = ssif_bmc_id,
> > > +};
> > > +
> > > +module_i2c_driver(ssif_bmc_driver);
> > > +
> > > +MODULE_AUTHOR("Quan Nguyen <[e-mail]>");
> > > +MODULE_AUTHOR("Chuong Tran <[e-mail]>");
> > > +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF interface.");
> > > +MODULE_LICENSE("GPL");
> > > diff --git a/drivers/char/ipmi/ssif_bmc.h b/drivers/char/ipmi/ssif_bmc.h
> > > new file mode 100644
> > > index 000000000000..9a26f3c252cc
> > > --- /dev/null
> > > +++ b/drivers/char/ipmi/ssif_bmc.h
> > > @@ -0,0 +1,102 @@
> > > +/* SPDX-License-Identifier: GPL-2.0+ */
> > > +/*
> > > + * The driver for BMC side of SSIF interface
> > > + *
> > > + * Copyright (c) 2022, Ampere Computing LLC
> > > + *
> > > + */
> > > +#ifndef __SSIF_BMC_H__
> > > +#define __SSIF_BMC_H__
> > > +
> > > +#define DEVICE_NAME				"ipmi-ssif-host"
> > > +
> > > +#define GET_8BIT_ADDR(addr_7bit)		(((addr_7bit) << 1) & 0xff)
> > > +
> > > +/* A standard SMBus Transaction is limited to 32 data bytes */
> > > +#define MAX_PAYLOAD_PER_TRANSACTION		32
> > > +
> > > +#define MAX_IPMI_DATA_PER_START_TRANSACTION	30
> > > +#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION	31
> > > +
> > > +#define SSIF_IPMI_SINGLEPART_WRITE		0x2
> > > +#define SSIF_IPMI_SINGLEPART_READ		0x3
> > > +#define SSIF_IPMI_MULTIPART_WRITE_START		0x6
> > > +#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE	0x7
> > > +#define SSIF_IPMI_MULTIPART_WRITE_END		0x8
> > > +#define SSIF_IPMI_MULTIPART_READ_START		0x3
> > > +#define SSIF_IPMI_MULTIPART_READ_MIDDLE		0x9
> > > +
> > > +#define MSG_PAYLOAD_LEN_MAX			252
> > > +/*
> > > + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
> > > + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
> > > + * Recover ssif_bmc from busy state if it takes upto 500ms
> > > + */
> > > +#define RESPONSE_TIMEOUT			500 /* ms */
> > > +
> > > +struct ssif_msg {
> > > +	u8 len;
> > > +	u8 netfn_lun;
> > > +	u8 cmd;
> > > +	u8 payload[MSG_PAYLOAD_LEN_MAX];
> > > +} __packed;
> > > +
> > > +static inline u32 ssif_msg_len(struct ssif_msg *ssif_msg)
> > > +{
> > > +	return ssif_msg->len + 1;
> > > +}
> > > +
> > > +/*
> > > + * SSIF internal states:
> > > + *   SSIF_READY         0x00 : Ready state
> > > + *   SSIF_START         0x01 : Start smbus transaction
> > > + *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
> > > + *   SSIF_REQ_RECVING   0x03 : Receiving request
> > > + *   SSIF_RES_SENDING   0x04 : Sending response
> > > + *   SSIF_BAD_SMBUS     0x05 : Bad SMbus transaction
> > > + */
> > > +enum ssif_state {
> > > +	SSIF_READY,
> > > +	SSIF_START,
> > > +	SSIF_SMBUS_CMD,
> > > +	SSIF_REQ_RECVING,
> > > +	SSIF_RES_SENDING,
> > > +	SSIF_BAD_SMBUS,
> > > +	SSIF_STATE_MAX
> > > +};
> > > +
> > > +struct ssif_bmc_ctx {
> > > +	struct i2c_client	*client;
> > > +	struct miscdevice	miscdev;
> > > +	size_t			msg_idx;
> > > +	bool			pec_support;
> > > +	/* ssif bmc spinlock */
> > > +	spinlock_t		lock;
> > > +	wait_queue_head_t	wait_queue;
> > > +	u8			running;
> > > +	enum ssif_state		state;
> > > +	u8			smbus_cmd;
> > > +	/* Timeout waiting for response */
> > > +	struct timer_list	response_timer;
> > > +	bool                    response_timer_inited;
> > > +	/* Flag to identify a Multi-part Read Transaction */
> > > +	bool			is_singlepart_read;
> > > +	u8			nbytes_processed;
> > > +	u8			remain_len;
> > > +	u8			recv_len;
> > > +	/* Block Number of a Multi-part Read Transaction */
> > > +	u8			block_num;
> > > +	bool			request_available;
> > > +	bool			response_in_progress;
> > > +	bool			busy;
> > > +	/* Response buffer for Multi-part Read Transaction */
> > > +	u8			response_buf[MAX_PAYLOAD_PER_TRANSACTION];
> > > +	struct ssif_msg		response;
> > > +	struct ssif_msg		request;
> > > +};
> > > +
> > > +static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
> > > +{
> > > +	return container_of(file->private_data, struct ssif_bmc_ctx, miscdev);
> > > +}
> > > +#endif /* __SSIF_BMC_H__ */
> > > -- 
> > > 2.35.1
> > > 
> > >

Quan Nguyen April 8, 2022, 4:40 a.m. UTC | #7

On 17/03/2022 20:13, Corey Minyard wrote:
> snip...
>>>> +
>>>> +static void response_timeout(struct timer_list *t)
>>>> +{
>>>> +	struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, response_timer);
>>>> +	unsigned long flags;
>>>> +
>>>
>>> Is there a possible race here?  The timeout can happen at the same time
>>> as a received message, will something bad happen if that's the case?
>>>
>>
>> Thanks Corey,
>> I think I need extra comment here.
>>
>> The purpose of this timeout is to make sure ssif_bmc will recover from busy
>> state in case the upper stack does not provide the response.
>> Hence, the response timeout is set as 500ms, twice the time of max
>> Request-to-Response in spec as the code below. Should it be longer?
> 
> That's not what I was asking.  I know what the timer is for.  But what
> happens if the response comes in at the same time this timer goes off?
> What will keep the data from getting messed up?
> 

Dear Corey, thanks for pointing this out.

In case the response comes in at the same time this timer goes off, both 
timeout handler and the ssif_bmc_write must first win to acquire the 
lock first, eg: ssif_bmc->lock

If timeout handler wins it firstly test ssif_bmc->response_in_progress 
to make sure if the ssif_bmc_write() is succeeded. If not, 
ssif_bmc->response_in_progress is false, then set the ssif_bmc->busy and 
ssif_bmc->response_timer_inited flags to false, and set the flag 
ssif_bmc->aborting = true to start aborting the current response.

If ssif_bmc_write() wins, it then first test if the timer not yet goes 
off, ie: ssif_bmc->response_timer_inited is true, if so, del the timer 
and let the response ready to send back to host. If not, make 
ssif_bmc_write() to return -EINVAL as the driver had already aborted the 
response and wait for the new request.

This will be included in my next version.

>>
>> As per spec, the max Request-to-Respose would not exceed 250ms.
>>
>> I put the comment in ssif_bmc.h as below:
>>>> +/*
>>>> + * IPMI 2.0 Spec, section 12.7 SSIF Timing,
>>>> + * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
>>>> + * Recover ssif_bmc from busy state if it takes upto 500ms
>>>> + */
>>>> +#define RESPONSE_TIMEOUT			500 /* ms */
>>
>>
>>>> +	spin_lock_irqsave(&ssif_bmc->lock, flags);
>>>> +
>>>> +	/* Recover ssif_bmc from busy */
>>>> +	ssif_bmc->busy = false;
>>>> +	del_timer(&ssif_bmc->response_timer);
>>>
>>> You don't need to delete the timer, it's in the timeout.
>>>
>>
>> Will remove this redundant code in next version
>>
>>>> +	ssif_bmc->response_timer_inited = false;
>>>> +
>>>> +	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>>>> +}
>>>> +
>>>> +/* Called with ssif_bmc->lock held. */
>>>> +static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
>>>> +{
>>>> +	/* set ssif_bmc to busy waiting for response */
>>>> +	ssif_bmc->busy = true;
>>>> +
>>>> +	/* Request message is available to process */
>>>> +	ssif_bmc->request_available = true;
>>>> +
>>>> +	/* Clean old response buffer */
>>>> +	memset(&ssif_bmc->response, 0, sizeof(struct ssif_msg));
>>>> +
>>>> +	/* This is the new READ request.*/
>>>> +	wake_up_all(&ssif_bmc->wait_queue);
>>>> +
>>>> +	/* Armed timer to recover slave from busy state in case of no response */
>>>> +	if (!ssif_bmc->response_timer_inited) {
>>>> +		timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
>>>> +		ssif_bmc->response_timer_inited = true;
>>>> +	}
>>>> +	mod_timer(&ssif_bmc->response_timer, jiffies + msecs_to_jiffies(RESPONSE_TIMEOUT));
>>>> +}
>>>> +
>>>> +static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>>>> +{
>>>> +	u8 response_len = 0;
>>>> +	int idx = 0;
>>>> +	u8 data_len;
>>>> +
>>>> +	data_len = ssif_bmc->response.len;
>>>> +	switch (ssif_bmc->smbus_cmd) {
>>>> +	case SSIF_IPMI_MULTIPART_READ_START:
>>>> +		/*
>>>> +		 * Read Start length is 32 bytes.
>>>> +		 * Read Start transfer first 30 bytes of IPMI response
>>>> +		 * and 2 special code 0x00, 0x01.
>>>> +		 */
>>>> +		*val = MAX_PAYLOAD_PER_TRANSACTION;
>>>> +		ssif_bmc->remain_len = data_len - MAX_IPMI_DATA_PER_START_TRANSACTION;
>>>> +		ssif_bmc->block_num = 0;
>>>
>>> Do you need to validate the data length before using this?
>>> This applies for lots of places through here.
>>>
>>
>> set_multipart_response_buffer() is called only when ->is_singlepart_read is
>> false, which is determined by the below code under the *_write()
>>
>> ssif_bmc->is_singlepart_read = (ssif_msg_len(&msg) <=
>> MAX_PAYLOAD_PER_TRANSACTION + 1);
>>
>> So, I think the len is validated and could be use in this functions.
> 
> Ah, I had things backwards.  "Read" here is when you are writing to
> the other side.  I understand now.
> 
>>
>>>> +
>>>> +		ssif_bmc->response_buf[idx++] = 0x00; /* Start Flag */
>>>> +		ssif_bmc->response_buf[idx++] = 0x01; /* Start Flag */
>>>> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.netfn_lun;
>>>> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.cmd;
>>>> +		ssif_bmc->response_buf[idx++] = ssif_bmc->response.payload[0];
>>>> +
>>>> +		response_len = MAX_PAYLOAD_PER_TRANSACTION - idx;
>>>> +
>>>> +		memcpy(&ssif_bmc->response_buf[idx], &ssif_bmc->response.payload[1],
>>>> +		       response_len);
>>>> +		break;
>>>> +
>>>> +	case SSIF_IPMI_MULTIPART_READ_MIDDLE:
>>>> +		/*
>>>> +		 * IPMI READ Middle or READ End messages can carry up to 31 bytes
>>>> +		 * IPMI data plus block number byte.
>>>> +		 */
>>>> +		if (ssif_bmc->remain_len < MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
>>>> +			/*
>>>> +			 * This is READ End message
>>>> +			 *  Return length is the remaining response data length
>>>> +			 *  plus block number
>>>> +			 *  Block number 0xFF is to indicate this is last message
>>>> +			 *
>>>> +			 */
>>>> +			*val = ssif_bmc->remain_len + 1;
>>>> +			ssif_bmc->block_num = 0xFF;
>>>> +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
>>>> +			response_len = ssif_bmc->remain_len;
>>>> +			/* Clean the buffer */
>>>> +			memset(&ssif_bmc->response_buf[idx], 0, MAX_PAYLOAD_PER_TRANSACTION - idx);
>>>> +		} else {
>>>> +			/*
>>>> +			 * This is READ Middle message
>>>> +			 *  Response length is the maximum SMBUS transfer length
>>>> +			 *  Block number byte is incremented
>>>> +			 * Return length is maximum SMBUS transfer length
>>>> +			 */
>>>> +			*val = MAX_PAYLOAD_PER_TRANSACTION;
>>>> +			ssif_bmc->remain_len -= MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>>>> +			response_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>>>> +			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
>>>> +			ssif_bmc->block_num++;
>>>> +		}
>>>> +
>>>> +		memcpy(&ssif_bmc->response_buf[idx],
>>>> +		       ssif_bmc->response.payload + 1 + ssif_bmc->nbytes_processed,
>>>> +		       response_len);
>>>> +		break;
>>>> +
>>>> +	default:
>>>> +		/* Do not expect to go to this case */
>>>> +		dev_err(&ssif_bmc->client->dev,
>>>> +			"%s: Unexpected SMBus command 0x%x\n",
>>>> +			__func__, ssif_bmc->smbus_cmd);
>>>> +		break;
>>>> +	}
>>>> +
>>>> +	ssif_bmc->nbytes_processed += response_len;
>>>> +}
>>>> +
>>>> +/* Process the IPMI response that will be read by master */
>>>> +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>>>> +{
>>>> +	u8 *buf;
>>>> +	u8 pec_len, addr, len;
>>>> +	u8 pec = 0;
>>>> +
>>>> +	pec_len = ssif_bmc->pec_support ? 1 : 0;
>>>> +	/* PEC - Start Read Address */
>>>> +	addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>>>> +	pec = i2c_smbus_pec(pec, &addr, 1);
>>>> +	/* PEC - SSIF Command */
>>>> +	pec = i2c_smbus_pec(pec, &ssif_bmc->smbus_cmd, 1);
>>>> +	/* PEC - Restart Write Address */
>>>> +	addr = addr | 0x01;
>>>> +	pec = i2c_smbus_pec(pec, &addr, 1);
>>>> +
>>>> +	if (ssif_bmc->is_singlepart_read) {
>>>> +		/* Single-part Read processing */
>>>> +		buf = (u8 *)&ssif_bmc->response;
>>>> +
>>>> +		if (ssif_bmc->response.len && ssif_bmc->msg_idx < ssif_bmc->response.len) {
>>>> +			ssif_bmc->msg_idx++;
>>>> +			*val = buf[ssif_bmc->msg_idx];
>>>> +		} else if (ssif_bmc->response.len && ssif_bmc->msg_idx == ssif_bmc->response.len) {
>>>> +			ssif_bmc->msg_idx++;
>>>> +			*val = i2c_smbus_pec(pec, buf, ssif_msg_len(&ssif_bmc->response));
>>>> +		} else {
>>>
>>> I thought for a second that this was wrong, but I think it's correct.
>>> Supply zero if you don't have data.
>>>
>>>> +			*val = 0;
>>>> +		}
>>>> +		/* Invalidate response buffer to denote it is sent */
>>>> +		if (ssif_bmc->msg_idx + 1 >= (ssif_msg_len(&ssif_bmc->response) + pec_len))
>>>> +			complete_response(ssif_bmc);
>>>> +	} else {
>>>> +		/* Multi-part Read processing */
>>>
>>> You don't check the length here like you did above.  I think that's
>>> required.
>>>
>>
>> As per my explanation above, the ->is_singlepart_read is determined by
>> testing the length, so it is validated as I assumed.
>>
>>>> +		switch (ssif_bmc->smbus_cmd) {
>>>> +		case SSIF_IPMI_MULTIPART_READ_START:
>>>> +		case SSIF_IPMI_MULTIPART_READ_MIDDLE:
>>>> +			buf = (u8 *)&ssif_bmc->response_buf;
>>>> +			*val = buf[ssif_bmc->msg_idx];
>>>> +			ssif_bmc->msg_idx++;
>>>> +			break;
>>>> +		default:
>>>> +			/* Do not expect to go to this case */
>>>> +			dev_err(&ssif_bmc->client->dev,
>>>> +				"%s: Unexpected SMBus command 0x%x\n",
>>>> +				__func__, ssif_bmc->smbus_cmd);
>>>> +			break;
>>>> +		}
>>>> +
>>>> +		len = (ssif_bmc->block_num == 0xFF) ?
>>>> +		       ssif_bmc->remain_len + 1 : MAX_PAYLOAD_PER_TRANSACTION;
>>>> +		if (ssif_bmc->msg_idx == (len + 1)) {
>>>> +			pec = i2c_smbus_pec(pec, &len, 1);
>>>> +			*val = i2c_smbus_pec(pec, ssif_bmc->response_buf, len);
>>>> +		}
>>>> +		/* Invalidate response buffer to denote last response is sent */
>>>> +		if (ssif_bmc->block_num == 0xFF &&
>>>> +		    ssif_bmc->msg_idx > (ssif_bmc->remain_len + pec_len)) {
>>>> +			complete_response(ssif_bmc);
>>>> +		}
>>>> +	}
>>>> +}
>>>> +
>>>> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>>>> +{
>>>> +	u8 *buf = (u8 *)&ssif_bmc->request;
>>>> +
>>>> +	if (ssif_bmc->msg_idx >= sizeof(struct ssif_msg))
>>>> +		return;
> 
> I don't think this check is valid.  I believe the msg_idx only covers
> the current message, but ssif_msg is a full multi-part message.  It
> covers the single-part message, I think but not the multi-part ones.
> Also, abort the operation and log on bad data.
> 

Yes, thank you for this catch.

Will change in next version.

>>>> +
>>>> +	switch (ssif_bmc->smbus_cmd) {
>>>> +	case SSIF_IPMI_SINGLEPART_WRITE:
>>>> +		buf[ssif_bmc->msg_idx - 1] = *val;
>>>> +		ssif_bmc->msg_idx++;
>>>> +
>>>> +		break;
>>>> +	case SSIF_IPMI_MULTIPART_WRITE_START:
>>>> +		if (ssif_bmc->msg_idx == 1)
>>>> +			ssif_bmc->request.len = 0;
>>>> +
>>>> +		fallthrough;
>>>> +	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
>>>> +		/* The len should always be 32 */
>>>> +		if (ssif_bmc->msg_idx == 1 && *val != MAX_PAYLOAD_PER_TRANSACTION)
>>>> +			dev_warn(&ssif_bmc->client->dev,
>>>> +				 "Warn: Invalid Multipart Write len");
> 
> You should abort the operation here.  Don't deliver obviously bad data.
> Same in the code just below.
> 
> This will require that you add a message aborted type of state to just
> ignore everything that comes in until the full sequence ends or a new
> message starts.
> 

Will introduce the abort state which will ignore everything until the 
new request comes to handle those invalid cases.

>>>> +
>>>> +		fallthrough;
>>>> +	case SSIF_IPMI_MULTIPART_WRITE_END:
>>>> +		/* Multi-part write, 2nd byte received is length */
>>>> +		if (ssif_bmc->msg_idx == 1) {
>>>> +			if (*val > MAX_PAYLOAD_PER_TRANSACTION)
>>>> +				dev_warn(&ssif_bmc->client->dev,
>>>> +					 "Warn: Invalid Multipart Write End len");
>>>> +
>>>> +			ssif_bmc->request.len += *val;
>>>> +			ssif_bmc->recv_len = *val;
>>>> +
>>>> +			/* request len should never exceeded 255 bytes */
>>>> +			if (ssif_bmc->request.len > 255)
>>>> +				dev_warn(&ssif_bmc->client->dev,
>>>> +					 "Warn: Invalid request len");
>>>> +
>>>> +		} else {
>>>
>>> You check msg_idx above, but I'm not sure that check will cover this
>>> operation.
>>>
>> That check is to make sure the length (*val) must always be strictly 32
>> bytes in case of MULTIPART_WRITE_START/MIDDLE. And this check allows the
>> length is up to 32 bytes in MULTIPART_WRITE_END.
> 
> Now that I have read and write straight, this is where the previous
> comments apply.
> 
> You are trusting the the length sent by the remote end in the second
> byte is correct, but there is no guarantee of this.  The remote end can
> send as many bytes as it likes.  You need to check that you don't
> overflow buf here and that it actually sends the number of bytes that it
> said it was going to send to avoid underflow.
> 

Will include in next version. The request which is exceeded the 255 
bytes should be aborted.

>>
>>>> +			buf[ssif_bmc->msg_idx - 1 +
>>>> +			    ssif_bmc->request.len - ssif_bmc->recv_len]	= *val;
> 
> This computation is fairly complicated and hard to understand.
> Calculations like this are asking for trouble.
> 
> It would be easier to understand had request.len be the current length
> of what is in request.payload and increment it on every incoming byte.
> Then request.len could be used to add data to the buffer, like
> 
> 	if (ssif_bmc->request.len >= sizeof(ssif_bmc->payload))
> 		error...
> 	ssif_bmc->payload[ssif_bmc->request.len++] = *val;
> 
> If you renamed msg_idx to curr_recv_idx and recv_len to curr_recv_len,
> it would be more clear that these are related and operate on the current
> incoming message.
> 
> It would also be nice to get rid of the casts from ssif_msg to a buffer
> array and just index directly into request.payload[].
> 

Really appreciate for these comments, Corey.
I have rechecked the code and there will be, definitely, changes to 
refactor this code in my next version.

> In thinking about this further, I have a few more observations...
> 
> There is no need to have the netfn and cmd in ssif_msg.  They are just
> the first and second bytes of the message.  You don't care what they
> are in this code.
> 
Agree. Will change in next version

> Why do you deliver the length as part of the message to the user?  The
> length is returned by the system call.  You have all these +1 and -1
> things around the message length, which is error-prone.  Removing the
> length from the message would get rid of all of that.  And using packed
> structures is generally not the best, anyway.
> 

Will avoid those +1, -1 in next version.
About the packed structures, I think it is needed because we want to 
just copy the whole request/response struct from/to user space.

> The PEC calculations remove one byte from the maximum message length.
> Since they are not included in the length byte, it's kind of unnatural
> to do this the way you are doing it.  Instead, it might be best to say
> if you receive a byte and curr_recv_idx == curr_recv_len, process it
> as PEC.  That way the PEC never hits the buffer.
> 
> There is no need for msg_idx, or cur_recv_idx, to be size_t.
> 
> I need to look at this some more, but I'll need to see the rewrite.
> 
> -corey
> 
Thanks Corey,

Will address these suggestions on next version.

- Quan

Patch

diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
index b061e6b513ed..18a89093d64e 100644
--- a/drivers/char/ipmi/Kconfig
+++ b/drivers/char/ipmi/Kconfig
@@ -169,6 +169,17 @@  config ASPEED_BT_IPMI_BMC
 	  found on Aspeed SOCs (AST2400 and AST2500). The driver
 	  implements the BMC side of the BT interface.
 
+config SSIF_IPMI_BMC
+	tristate "SSIF IPMI BMC driver"
+	select I2C
+	select I2C_SLAVE
+	help
+	  This enables the IPMI SMBus system interface (SSIF) at the
+	  management (BMC) side.
+
+	  The driver implements the BMC side of the SMBus system
+	  interface (SSIF).
+
 config IPMB_DEVICE_INTERFACE
 	tristate 'IPMB Interface handler'
 	depends on I2C
diff --git a/drivers/char/ipmi/Makefile b/drivers/char/ipmi/Makefile
index 7ce790efad92..cb6138b8ded9 100644
--- a/drivers/char/ipmi/Makefile
+++ b/drivers/char/ipmi/Makefile
@@ -30,3 +30,4 @@  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
+obj-$(CONFIG_SSIF_IPMI_BMC) += ssif_bmc.o
diff --git a/drivers/char/ipmi/ssif_bmc.c b/drivers/char/ipmi/ssif_bmc.c
new file mode 100644
index 000000000000..62db97773654
--- /dev/null
+++ b/drivers/char/ipmi/ssif_bmc.c
@@ -0,0 +1,791 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * The driver for BMC side of SSIF interface
+ *
+ * Copyright (c) 2022, Ampere Computing LLC
+ *
+ */
+
+#include <linux/i2c.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/poll.h>
+#include <linux/sched.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+#include <linux/timer.h>
+#include <linux/jiffies.h>
+
+#include "ssif_bmc.h"
+
+static const char *state_to_string(enum ssif_state state)
+{
+	switch (state) {
+	case SSIF_READY:
+		return "SSIF_READY";
+	case SSIF_START:
+		return "SSIF_START";
+	case SSIF_SMBUS_CMD:
+		return "SSIF_SMBUS_CMD";
+	case SSIF_REQ_RECVING:
+		return "SSIF_REQ_RECVING";
+	case SSIF_RES_SENDING:
+		return "SSIF_RES_SENDING";
+	case SSIF_BAD_SMBUS:
+		return "SSIF_BAD_SMBUS";
+	default:
+		return "SSIF_STATE_UNKNOWN";
+	}
+}
+
+/* Handle SSIF message that will be sent to user */
+static ssize_t ssif_bmc_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
+{
+	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
+	struct ssif_msg msg;
+	unsigned long flags;
+	ssize_t ret;
+
+	spin_lock_irqsave(&ssif_bmc->lock, flags);
+	while (!ssif_bmc->request_available) {
+		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+		ret = wait_event_interruptible(ssif_bmc->wait_queue,
+					       ssif_bmc->request_available);
+		if (ret)
+			return ret;
+		spin_lock_irqsave(&ssif_bmc->lock, flags);
+	}
+
+	if (count < min_t(ssize_t, ssif_msg_len(&ssif_bmc->request), sizeof(struct ssif_msg))) {
+		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
+		ret = -EINVAL;
+	} else {
+		count = min_t(ssize_t, ssif_msg_len(&ssif_bmc->request), sizeof(struct ssif_msg));
+		memcpy(&msg, &ssif_bmc->request, count);
+		ssif_bmc->request_available = false;
+		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
+
+		ret = copy_to_user(buf, &msg, count);
+	}
+
+	return (ret < 0) ? ret : count;
+}
+
+/* Handle SSIF message that is written by user */
+static ssize_t ssif_bmc_write(struct file *file, const char __user *buf, size_t count,
+			      loff_t *ppos)
+{
+	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
+	struct ssif_msg msg;
+	unsigned long flags;
+	ssize_t ret;
+
+	if (count > sizeof(struct ssif_msg))
+		return -EINVAL;
+
+	ret = copy_from_user(&msg, buf, count);
+	if (ret)
+		return ret;
+
+	if (!msg.len || count < ssif_msg_len(&msg))
+		return -EINVAL;
+
+	spin_lock_irqsave(&ssif_bmc->lock, flags);
+	while (ssif_bmc->response_in_progress) {
+		spin_unlock_irqrestore(&ssif_bmc->lock, flags);
+		if (file->f_flags & O_NONBLOCK)
+			return -EAGAIN;
+		ret = wait_event_interruptible(ssif_bmc->wait_queue,
+					       !ssif_bmc->response_in_progress);
+		if (ret)
+			return ret;
+		spin_lock_irqsave(&ssif_bmc->lock, flags);
+	}
+
+	memcpy(&ssif_bmc->response, &msg, count);
+	ssif_bmc->is_singlepart_read = (ssif_msg_len(&msg) <= MAX_PAYLOAD_PER_TRANSACTION + 1);
+
+	ssif_bmc->response_in_progress = true;
+
+	/* ssif_bmc not busy */
+	ssif_bmc->busy = false;
+
+	if (ssif_bmc->response_timer_inited) {
+		del_timer(&ssif_bmc->response_timer);
+		ssif_bmc->response_timer_inited = false;
+	}
+	/* Clean old request buffer */
+	memset(&ssif_bmc->request, 0, sizeof(struct ssif_msg));
+
+	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
+
+	return count;
+}
+
+static int ssif_bmc_open(struct inode *inode, struct file *file)
+{
+	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
+	int ret = 0;
+
+	spin_lock_irq(&ssif_bmc->lock);
+	if (!ssif_bmc->running)
+		ssif_bmc->running = 1;
+	else
+		ret = -EBUSY;
+	spin_unlock_irq(&ssif_bmc->lock);
+
+	return ret;
+}
+
+static unsigned int ssif_bmc_poll(struct file *file, poll_table *wait)
+{
+	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
+	unsigned int mask = 0;
+
+	poll_wait(file, &ssif_bmc->wait_queue, wait);
+
+	spin_lock_irq(&ssif_bmc->lock);
+	/* The request is available, userspace application can get the request */
+	if (ssif_bmc->request_available)
+		mask |= POLLIN;
+
+	spin_unlock_irq(&ssif_bmc->lock);
+
+	return mask;
+}
+
+static int ssif_bmc_release(struct inode *inode, struct file *file)
+{
+	struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
+
+	spin_lock_irq(&ssif_bmc->lock);
+	ssif_bmc->running = 0;
+	spin_unlock_irq(&ssif_bmc->lock);
+
+	return 0;
+}
+
+/*
+ * System calls to device interface for user apps
+ */
+static const struct file_operations ssif_bmc_fops = {
+	.owner		= THIS_MODULE,
+	.open		= ssif_bmc_open,
+	.read		= ssif_bmc_read,
+	.write		= ssif_bmc_write,
+	.release	= ssif_bmc_release,
+	.poll		= ssif_bmc_poll,
+};
+
+/* Called with ssif_bmc->lock held. */
+static void complete_response(struct ssif_bmc_ctx *ssif_bmc)
+{
+	/* Invalidate response in buffer to denote it having been sent. */
+	ssif_bmc->response.len = 0;
+	ssif_bmc->response_in_progress = false;
+	ssif_bmc->nbytes_processed = 0;
+	ssif_bmc->remain_len = 0;
+	ssif_bmc->busy = false;
+	memset(&ssif_bmc->response_buf, 0, MAX_PAYLOAD_PER_TRANSACTION);
+	wake_up_all(&ssif_bmc->wait_queue);
+}
+
+static void response_timeout(struct timer_list *t)
+{
+	struct ssif_bmc_ctx *ssif_bmc = from_timer(ssif_bmc, t, response_timer);
+	unsigned long flags;
+
+	spin_lock_irqsave(&ssif_bmc->lock, flags);
+
+	/* Recover ssif_bmc from busy */
+	ssif_bmc->busy = false;
+	del_timer(&ssif_bmc->response_timer);
+	ssif_bmc->response_timer_inited = false;
+
+	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
+}
+
+/* Called with ssif_bmc->lock held. */
+static void handle_request(struct ssif_bmc_ctx *ssif_bmc)
+{
+	/* set ssif_bmc to busy waiting for response */
+	ssif_bmc->busy = true;
+
+	/* Request message is available to process */
+	ssif_bmc->request_available = true;
+
+	/* Clean old response buffer */
+	memset(&ssif_bmc->response, 0, sizeof(struct ssif_msg));
+
+	/* This is the new READ request.*/
+	wake_up_all(&ssif_bmc->wait_queue);
+
+	/* Armed timer to recover slave from busy state in case of no response */
+	if (!ssif_bmc->response_timer_inited) {
+		timer_setup(&ssif_bmc->response_timer, response_timeout, 0);
+		ssif_bmc->response_timer_inited = true;
+	}
+	mod_timer(&ssif_bmc->response_timer, jiffies + msecs_to_jiffies(RESPONSE_TIMEOUT));
+}
+
+static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	u8 response_len = 0;
+	int idx = 0;
+	u8 data_len;
+
+	data_len = ssif_bmc->response.len;
+	switch (ssif_bmc->smbus_cmd) {
+	case SSIF_IPMI_MULTIPART_READ_START:
+		/*
+		 * Read Start length is 32 bytes.
+		 * Read Start transfer first 30 bytes of IPMI response
+		 * and 2 special code 0x00, 0x01.
+		 */
+		*val = MAX_PAYLOAD_PER_TRANSACTION;
+		ssif_bmc->remain_len = data_len - MAX_IPMI_DATA_PER_START_TRANSACTION;
+		ssif_bmc->block_num = 0;
+
+		ssif_bmc->response_buf[idx++] = 0x00; /* Start Flag */
+		ssif_bmc->response_buf[idx++] = 0x01; /* Start Flag */
+		ssif_bmc->response_buf[idx++] = ssif_bmc->response.netfn_lun;
+		ssif_bmc->response_buf[idx++] = ssif_bmc->response.cmd;
+		ssif_bmc->response_buf[idx++] = ssif_bmc->response.payload[0];
+
+		response_len = MAX_PAYLOAD_PER_TRANSACTION - idx;
+
+		memcpy(&ssif_bmc->response_buf[idx], &ssif_bmc->response.payload[1],
+		       response_len);
+		break;
+
+	case SSIF_IPMI_MULTIPART_READ_MIDDLE:
+		/*
+		 * IPMI READ Middle or READ End messages can carry up to 31 bytes
+		 * IPMI data plus block number byte.
+		 */
+		if (ssif_bmc->remain_len < MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION) {
+			/*
+			 * This is READ End message
+			 *  Return length is the remaining response data length
+			 *  plus block number
+			 *  Block number 0xFF is to indicate this is last message
+			 *
+			 */
+			*val = ssif_bmc->remain_len + 1;
+			ssif_bmc->block_num = 0xFF;
+			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
+			response_len = ssif_bmc->remain_len;
+			/* Clean the buffer */
+			memset(&ssif_bmc->response_buf[idx], 0, MAX_PAYLOAD_PER_TRANSACTION - idx);
+		} else {
+			/*
+			 * This is READ Middle message
+			 *  Response length is the maximum SMBUS transfer length
+			 *  Block number byte is incremented
+			 * Return length is maximum SMBUS transfer length
+			 */
+			*val = MAX_PAYLOAD_PER_TRANSACTION;
+			ssif_bmc->remain_len -= MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
+			response_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
+			ssif_bmc->response_buf[idx++] = ssif_bmc->block_num;
+			ssif_bmc->block_num++;
+		}
+
+		memcpy(&ssif_bmc->response_buf[idx],
+		       ssif_bmc->response.payload + 1 + ssif_bmc->nbytes_processed,
+		       response_len);
+		break;
+
+	default:
+		/* Do not expect to go to this case */
+		dev_err(&ssif_bmc->client->dev,
+			"%s: Unexpected SMBus command 0x%x\n",
+			__func__, ssif_bmc->smbus_cmd);
+		break;
+	}
+
+	ssif_bmc->nbytes_processed += response_len;
+}
+
+/* Process the IPMI response that will be read by master */
+static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	u8 *buf;
+	u8 pec_len, addr, len;
+	u8 pec = 0;
+
+	pec_len = ssif_bmc->pec_support ? 1 : 0;
+	/* PEC - Start Read Address */
+	addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
+	pec = i2c_smbus_pec(pec, &addr, 1);
+	/* PEC - SSIF Command */
+	pec = i2c_smbus_pec(pec, &ssif_bmc->smbus_cmd, 1);
+	/* PEC - Restart Write Address */
+	addr = addr | 0x01;
+	pec = i2c_smbus_pec(pec, &addr, 1);
+
+	if (ssif_bmc->is_singlepart_read) {
+		/* Single-part Read processing */
+		buf = (u8 *)&ssif_bmc->response;
+
+		if (ssif_bmc->response.len && ssif_bmc->msg_idx < ssif_bmc->response.len) {
+			ssif_bmc->msg_idx++;
+			*val = buf[ssif_bmc->msg_idx];
+		} else if (ssif_bmc->response.len && ssif_bmc->msg_idx == ssif_bmc->response.len) {
+			ssif_bmc->msg_idx++;
+			*val = i2c_smbus_pec(pec, buf, ssif_msg_len(&ssif_bmc->response));
+		} else {
+			*val = 0;
+		}
+		/* Invalidate response buffer to denote it is sent */
+		if (ssif_bmc->msg_idx + 1 >= (ssif_msg_len(&ssif_bmc->response) + pec_len))
+			complete_response(ssif_bmc);
+	} else {
+		/* Multi-part Read processing */
+		switch (ssif_bmc->smbus_cmd) {
+		case SSIF_IPMI_MULTIPART_READ_START:
+		case SSIF_IPMI_MULTIPART_READ_MIDDLE:
+			buf = (u8 *)&ssif_bmc->response_buf;
+			*val = buf[ssif_bmc->msg_idx];
+			ssif_bmc->msg_idx++;
+			break;
+		default:
+			/* Do not expect to go to this case */
+			dev_err(&ssif_bmc->client->dev,
+				"%s: Unexpected SMBus command 0x%x\n",
+				__func__, ssif_bmc->smbus_cmd);
+			break;
+		}
+
+		len = (ssif_bmc->block_num == 0xFF) ?
+		       ssif_bmc->remain_len + 1 : MAX_PAYLOAD_PER_TRANSACTION;
+		if (ssif_bmc->msg_idx == (len + 1)) {
+			pec = i2c_smbus_pec(pec, &len, 1);
+			*val = i2c_smbus_pec(pec, ssif_bmc->response_buf, len);
+		}
+		/* Invalidate response buffer to denote last response is sent */
+		if (ssif_bmc->block_num == 0xFF &&
+		    ssif_bmc->msg_idx > (ssif_bmc->remain_len + pec_len)) {
+			complete_response(ssif_bmc);
+		}
+	}
+}
+
+static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	u8 *buf = (u8 *)&ssif_bmc->request;
+
+	if (ssif_bmc->msg_idx >= sizeof(struct ssif_msg))
+		return;
+
+	switch (ssif_bmc->smbus_cmd) {
+	case SSIF_IPMI_SINGLEPART_WRITE:
+		buf[ssif_bmc->msg_idx - 1] = *val;
+		ssif_bmc->msg_idx++;
+
+		break;
+	case SSIF_IPMI_MULTIPART_WRITE_START:
+		if (ssif_bmc->msg_idx == 1)
+			ssif_bmc->request.len = 0;
+
+		fallthrough;
+	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
+		/* The len should always be 32 */
+		if (ssif_bmc->msg_idx == 1 && *val != MAX_PAYLOAD_PER_TRANSACTION)
+			dev_warn(&ssif_bmc->client->dev,
+				 "Warn: Invalid Multipart Write len");
+
+		fallthrough;
+	case SSIF_IPMI_MULTIPART_WRITE_END:
+		/* Multi-part write, 2nd byte received is length */
+		if (ssif_bmc->msg_idx == 1) {
+			if (*val > MAX_PAYLOAD_PER_TRANSACTION)
+				dev_warn(&ssif_bmc->client->dev,
+					 "Warn: Invalid Multipart Write End len");
+
+			ssif_bmc->request.len += *val;
+			ssif_bmc->recv_len = *val;
+
+			/* request len should never exceeded 255 bytes */
+			if (ssif_bmc->request.len > 255)
+				dev_warn(&ssif_bmc->client->dev,
+					 "Warn: Invalid request len");
+
+		} else {
+			buf[ssif_bmc->msg_idx - 1 +
+			    ssif_bmc->request.len - ssif_bmc->recv_len]	= *val;
+		}
+
+		ssif_bmc->msg_idx++;
+
+		break;
+	default:
+		/* Do not expect to go to this case */
+		dev_err(&ssif_bmc->client->dev,
+			"%s: Unexpected SMBus command 0x%x\n",
+			__func__, ssif_bmc->smbus_cmd);
+		break;
+	}
+}
+
+static bool validate_request(struct ssif_bmc_ctx *ssif_bmc)
+{
+	u8 rpec = 0, cpec = 0;
+	bool ret = true;
+	u8 addr, index;
+	u8 *buf;
+
+	buf = (u8 *)&ssif_bmc->request;
+	switch (ssif_bmc->smbus_cmd) {
+	case SSIF_IPMI_SINGLEPART_WRITE:
+		if ((ssif_bmc->msg_idx - 1) == ssif_msg_len(&ssif_bmc->request)) {
+			/* PEC is not included */
+			ssif_bmc->pec_support = false;
+			ret = true;
+			goto exit;
+		}
+
+		if ((ssif_bmc->msg_idx - 1) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
+			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
+				ssif_msg_len(&ssif_bmc->request));
+			ret = false;
+			goto exit;
+		}
+
+		/* PEC is included */
+		ssif_bmc->pec_support = true;
+		rpec = buf[ssif_bmc->msg_idx - 2];
+		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
+		cpec = i2c_smbus_pec(cpec, &addr, 1);
+		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
+		cpec = i2c_smbus_pec(cpec, buf, ssif_msg_len(&ssif_bmc->request));
+		if (rpec != cpec) {
+			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
+			ret = false;
+		}
+
+		break;
+	case SSIF_IPMI_MULTIPART_WRITE_START:
+	case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
+	case SSIF_IPMI_MULTIPART_WRITE_END:
+		index = ssif_bmc->request.len - ssif_bmc->recv_len;
+		if ((ssif_bmc->msg_idx - 1 + index) == ssif_msg_len(&ssif_bmc->request)) {
+			/* PEC is not included */
+			ssif_bmc->pec_support = false;
+			ret = true;
+			goto exit;
+		}
+
+		if ((ssif_bmc->msg_idx - 1 + index) != (ssif_msg_len(&ssif_bmc->request) + 1)) {
+			dev_err(&ssif_bmc->client->dev, "Error: Unexpected length received %d\n",
+				ssif_msg_len(&ssif_bmc->request));
+			ret = false;
+			goto exit;
+		}
+
+		/* PEC is included */
+		ssif_bmc->pec_support = true;
+		rpec = buf[ssif_bmc->msg_idx - 2 + index];
+		addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
+		cpec = i2c_smbus_pec(cpec, &addr, 1);
+		cpec = i2c_smbus_pec(cpec, &ssif_bmc->smbus_cmd, 1);
+		cpec = i2c_smbus_pec(cpec, &ssif_bmc->recv_len, 1);
+		/* As SMBus specification does not allow the length
+		 * (byte count) in the Write-Block protocol to be zero.
+		 * Therefore, it is illegal to have the last Middle
+		 * transaction in the sequence carry 32-byte and have
+		 * a length of ‘0’ in the End transaction.
+		 * But some users may try to use this way and we should
+		 * prevent ssif_bmc driver broken in this case.
+		 */
+		if (ssif_bmc->recv_len != 0)
+			cpec = i2c_smbus_pec(cpec, buf + 1 + index, ssif_bmc->recv_len);
+
+		if (rpec != cpec) {
+			dev_err(&ssif_bmc->client->dev, "Bad PEC 0x%02x vs. 0x%02x\n", rpec, cpec);
+			ret = false;
+		}
+
+		break;
+	default:
+		/* Do not expect to go to this case */
+		dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 0x%x\n",
+			__func__, ssif_bmc->smbus_cmd);
+		ret = false;
+		break;
+	}
+
+exit:
+	return ret;
+}
+
+static bool unsupported_smbus_cmd(u8 cmd)
+{
+	if (cmd == SSIF_IPMI_SINGLEPART_READ ||
+	    cmd == SSIF_IPMI_SINGLEPART_WRITE ||
+	    cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
+	    cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
+	    cmd == SSIF_IPMI_MULTIPART_WRITE_END ||
+	    cmd == SSIF_IPMI_MULTIPART_READ_START ||
+	    cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
+		return false;
+
+	return true;
+}
+
+static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	/* SMBUS command can vary (single or multi-part) */
+	ssif_bmc->smbus_cmd = *val;
+	ssif_bmc->msg_idx++;
+
+	if (unsupported_smbus_cmd(*val))
+		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus command");
+
+	if (*val == SSIF_IPMI_SINGLEPART_WRITE ||
+	    *val == SSIF_IPMI_MULTIPART_WRITE_START) {
+		/*
+		 * The response maybe not come in-time, causing host SSIF driver
+		 * to timeout and resend a new request. In such case check for
+		 * pending response and clear it
+		 */
+		if (ssif_bmc->response_in_progress)
+			complete_response(ssif_bmc);
+	}
+}
+
+static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	if (ssif_bmc->state == SSIF_READY ||
+	    ssif_bmc->state == SSIF_START ||
+	    ssif_bmc->state == SSIF_REQ_RECVING ||
+	    ssif_bmc->state == SSIF_RES_SENDING) {
+		ssif_bmc->state = SSIF_BAD_SMBUS;
+		dev_warn(&ssif_bmc->client->dev,
+			 "Warn: %s unexpected READ REQUESTED in state=%s\n",
+			 __func__, state_to_string(ssif_bmc->state));
+
+	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
+		ssif_bmc->state = SSIF_RES_SENDING;
+	}
+
+	ssif_bmc->msg_idx = 0;
+	if (ssif_bmc->is_singlepart_read)
+		*val = ssif_bmc->response.len;
+	else
+		set_multipart_response_buffer(ssif_bmc, val);
+}
+
+static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	if (ssif_bmc->state == SSIF_READY ||
+	    ssif_bmc->state == SSIF_START ||
+	    ssif_bmc->state == SSIF_REQ_RECVING ||
+	    ssif_bmc->state == SSIF_SMBUS_CMD) {
+		dev_warn(&ssif_bmc->client->dev,
+			 "Warn: %s unexpected READ PROCESSED in state=%s\n",
+			 __func__, state_to_string(ssif_bmc->state));
+		ssif_bmc->state = SSIF_BAD_SMBUS;
+	}
+
+	handle_read_processed(ssif_bmc, val);
+}
+
+static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	ssif_bmc->msg_idx = 0;
+
+	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_SMBUS_CMD) {
+		ssif_bmc->state = SSIF_START;
+
+	} else if (ssif_bmc->state == SSIF_START ||
+		   ssif_bmc->state == SSIF_REQ_RECVING ||
+		   ssif_bmc->state == SSIF_RES_SENDING) {
+		dev_warn(&ssif_bmc->client->dev,
+			 "Warn: %s unexpected WRITE REQUEST in state=%s\n",
+			 __func__, state_to_string(ssif_bmc->state));
+		ssif_bmc->state = SSIF_BAD_SMBUS;
+	}
+}
+
+static void on_write_received_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	if (ssif_bmc->state == SSIF_READY || ssif_bmc->state == SSIF_RES_SENDING) {
+		dev_warn(&ssif_bmc->client->dev,
+			 "Warn: %s unexpected WRITE RECEIVED in state=%s\n",
+			 __func__, state_to_string(ssif_bmc->state));
+		ssif_bmc->state = SSIF_BAD_SMBUS;
+	} else if (ssif_bmc->state == SSIF_START) {
+		ssif_bmc->state = SSIF_SMBUS_CMD;
+	} else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
+		ssif_bmc->state = SSIF_REQ_RECVING;
+	}
+
+	/* This is response sending state */
+	if (ssif_bmc->state == SSIF_REQ_RECVING)
+		handle_write_received(ssif_bmc, val);
+	else if (ssif_bmc->state == SSIF_SMBUS_CMD)
+		process_smbus_cmd(ssif_bmc, val);
+}
+
+static void on_stop_event(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
+{
+	if (ssif_bmc->state == SSIF_READY ||
+	    ssif_bmc->state == SSIF_START ||
+	    ssif_bmc->state == SSIF_SMBUS_CMD) {
+		dev_warn(&ssif_bmc->client->dev,
+			 "Warn: %s unexpected SLAVE STOP in state=%s\n",
+			 __func__, state_to_string(ssif_bmc->state));
+
+	} else if (ssif_bmc->state == SSIF_BAD_SMBUS) {
+		dev_warn(&ssif_bmc->client->dev,
+			 "Warn: %s received SLAVE STOP from bad state=%s\n",
+			 __func__, state_to_string(ssif_bmc->state));
+
+	} else if (ssif_bmc->state == SSIF_REQ_RECVING) {
+		/* A BMC that receives an invalid request drop the data for the write
+		 * transaction and any further transactions (read or write) until
+		 * the next valid read or write Start transaction is received
+		 */
+		if (!validate_request(ssif_bmc))
+			dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
+		else if (ssif_bmc->smbus_cmd == SSIF_IPMI_SINGLEPART_WRITE ||
+			 ssif_bmc->smbus_cmd == SSIF_IPMI_MULTIPART_WRITE_END)
+			handle_request(ssif_bmc);
+	}
+
+	ssif_bmc->state = SSIF_READY;
+	/* Reset message index */
+	ssif_bmc->msg_idx = 0;
+}
+
+/*
+ * Callback function to handle I2C slave events
+ */
+static int ssif_bmc_cb(struct i2c_client *client, enum i2c_slave_event event, u8 *val)
+{
+	unsigned long flags;
+	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
+	int ret = 0;
+
+	spin_lock_irqsave(&ssif_bmc->lock, flags);
+
+	switch (event) {
+	case I2C_SLAVE_READ_REQUESTED:
+		on_read_requested_event(ssif_bmc, val);
+		break;
+
+	case I2C_SLAVE_WRITE_REQUESTED:
+		on_write_requested_event(ssif_bmc, val);
+		break;
+
+	case I2C_SLAVE_READ_PROCESSED:
+		on_read_processed_event(ssif_bmc, val);
+		break;
+
+	case I2C_SLAVE_WRITE_RECEIVED:
+		on_write_received_event(ssif_bmc, val);
+		break;
+
+	case I2C_SLAVE_STOP:
+		on_stop_event(ssif_bmc, val);
+		break;
+
+	default:
+		dev_warn(&ssif_bmc->client->dev, "Warn: Unknown i2c slave event\n");
+		break;
+	}
+
+	if (ssif_bmc->busy)
+		ret = -EBUSY;
+
+	spin_unlock_irqrestore(&ssif_bmc->lock, flags);
+
+	return ret;
+}
+
+static int ssif_bmc_probe(struct i2c_client *client, const struct i2c_device_id *id)
+{
+	struct ssif_bmc_ctx *ssif_bmc;
+	int ret;
+
+	ssif_bmc = devm_kzalloc(&client->dev, sizeof(*ssif_bmc), GFP_KERNEL);
+	if (!ssif_bmc)
+		return -ENOMEM;
+
+	spin_lock_init(&ssif_bmc->lock);
+
+	init_waitqueue_head(&ssif_bmc->wait_queue);
+	ssif_bmc->request_available = false;
+	ssif_bmc->response_in_progress = false;
+	ssif_bmc->busy = false;
+	ssif_bmc->response_timer_inited = false;
+
+	/* Register misc device interface */
+	ssif_bmc->miscdev.minor = MISC_DYNAMIC_MINOR;
+	ssif_bmc->miscdev.name = DEVICE_NAME;
+	ssif_bmc->miscdev.fops = &ssif_bmc_fops;
+	ssif_bmc->miscdev.parent = &client->dev;
+	ret = misc_register(&ssif_bmc->miscdev);
+	if (ret)
+		goto out;
+
+	ssif_bmc->client = client;
+	ssif_bmc->client->flags |= I2C_CLIENT_SLAVE;
+
+	/* Register I2C slave */
+	i2c_set_clientdata(client, ssif_bmc);
+	ret = i2c_slave_register(client, ssif_bmc_cb);
+	if (ret) {
+		misc_deregister(&ssif_bmc->miscdev);
+		goto out;
+	}
+
+	return 0;
+out:
+	devm_kfree(&client->dev, ssif_bmc);
+	return ret;
+}
+
+static int ssif_bmc_remove(struct i2c_client *client)
+{
+	struct ssif_bmc_ctx *ssif_bmc = i2c_get_clientdata(client);
+
+	i2c_slave_unregister(client);
+	misc_deregister(&ssif_bmc->miscdev);
+
+	return 0;
+}
+
+static const struct of_device_id ssif_bmc_match[] = {
+	{ .compatible = "ampere,ssif-bmc" },
+	{ },
+};
+
+static const struct i2c_device_id ssif_bmc_id[] = {
+	{ DEVICE_NAME, 0 },
+	{ },
+};
+
+MODULE_DEVICE_TABLE(i2c, ssif_bmc_id);
+
+static struct i2c_driver ssif_bmc_driver = {
+	.driver         = {
+		.name           = DEVICE_NAME,
+		.of_match_table = ssif_bmc_match,
+	},
+	.probe          = ssif_bmc_probe,
+	.remove         = ssif_bmc_remove,
+	.id_table       = ssif_bmc_id,
+};
+
+module_i2c_driver(ssif_bmc_driver);
+
+MODULE_AUTHOR("Quan Nguyen <[e-mail]>");
+MODULE_AUTHOR("Chuong Tran <[e-mail]>");
+MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF interface.");
+MODULE_LICENSE("GPL");
diff --git a/drivers/char/ipmi/ssif_bmc.h b/drivers/char/ipmi/ssif_bmc.h
new file mode 100644
index 000000000000..9a26f3c252cc
--- /dev/null
+++ b/drivers/char/ipmi/ssif_bmc.h
@@ -0,0 +1,102 @@ 
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * The driver for BMC side of SSIF interface
+ *
+ * Copyright (c) 2022, Ampere Computing LLC
+ *
+ */
+#ifndef __SSIF_BMC_H__
+#define __SSIF_BMC_H__
+
+#define DEVICE_NAME				"ipmi-ssif-host"
+
+#define GET_8BIT_ADDR(addr_7bit)		(((addr_7bit) << 1) & 0xff)
+
+/* A standard SMBus Transaction is limited to 32 data bytes */
+#define MAX_PAYLOAD_PER_TRANSACTION		32
+
+#define MAX_IPMI_DATA_PER_START_TRANSACTION	30
+#define MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION	31
+
+#define SSIF_IPMI_SINGLEPART_WRITE		0x2
+#define SSIF_IPMI_SINGLEPART_READ		0x3
+#define SSIF_IPMI_MULTIPART_WRITE_START		0x6
+#define SSIF_IPMI_MULTIPART_WRITE_MIDDLE	0x7
+#define SSIF_IPMI_MULTIPART_WRITE_END		0x8
+#define SSIF_IPMI_MULTIPART_READ_START		0x3
+#define SSIF_IPMI_MULTIPART_READ_MIDDLE		0x9
+
+#define MSG_PAYLOAD_LEN_MAX			252
+/*
+ * IPMI 2.0 Spec, section 12.7 SSIF Timing,
+ * Request-to-Response Time is T6max(250ms) - T1max(20ms) - 3ms = 227ms
+ * Recover ssif_bmc from busy state if it takes upto 500ms
+ */
+#define RESPONSE_TIMEOUT			500 /* ms */
+
+struct ssif_msg {
+	u8 len;
+	u8 netfn_lun;
+	u8 cmd;
+	u8 payload[MSG_PAYLOAD_LEN_MAX];
+} __packed;
+
+static inline u32 ssif_msg_len(struct ssif_msg *ssif_msg)
+{
+	return ssif_msg->len + 1;
+}
+
+/*
+ * SSIF internal states:
+ *   SSIF_READY         0x00 : Ready state
+ *   SSIF_START         0x01 : Start smbus transaction
+ *   SSIF_SMBUS_CMD     0x02 : Received SMBus command
+ *   SSIF_REQ_RECVING   0x03 : Receiving request
+ *   SSIF_RES_SENDING   0x04 : Sending response
+ *   SSIF_BAD_SMBUS     0x05 : Bad SMbus transaction
+ */
+enum ssif_state {
+	SSIF_READY,
+	SSIF_START,
+	SSIF_SMBUS_CMD,
+	SSIF_REQ_RECVING,
+	SSIF_RES_SENDING,
+	SSIF_BAD_SMBUS,
+	SSIF_STATE_MAX
+};
+
+struct ssif_bmc_ctx {
+	struct i2c_client	*client;
+	struct miscdevice	miscdev;
+	size_t			msg_idx;
+	bool			pec_support;
+	/* ssif bmc spinlock */
+	spinlock_t		lock;
+	wait_queue_head_t	wait_queue;
+	u8			running;
+	enum ssif_state		state;
+	u8			smbus_cmd;
+	/* Timeout waiting for response */
+	struct timer_list	response_timer;
+	bool                    response_timer_inited;
+	/* Flag to identify a Multi-part Read Transaction */
+	bool			is_singlepart_read;
+	u8			nbytes_processed;
+	u8			remain_len;
+	u8			recv_len;
+	/* Block Number of a Multi-part Read Transaction */
+	u8			block_num;
+	bool			request_available;
+	bool			response_in_progress;
+	bool			busy;
+	/* Response buffer for Multi-part Read Transaction */
+	u8			response_buf[MAX_PAYLOAD_PER_TRANSACTION];
+	struct ssif_msg		response;
+	struct ssif_msg		request;
+};
+
+static inline struct ssif_bmc_ctx *to_ssif_bmc(struct file *file)
+{
+	return container_of(file->private_data, struct ssif_bmc_ctx, miscdev);
+}
+#endif /* __SSIF_BMC_H__ */