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Date:   Mon, 10 Oct 2022 08:28:24 +0700
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Subject: Re: [PATCH v10 1/3] ipmi: ssif_bmc: Add SSIF BMC driver
Content-Language: en-CA
To:     Graeme Gregory <quic_ggregory@quicinc.com>
Cc:     thang@os.amperecomputing.com,
        Phong Vo <phong@os.amperecomputing.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Wolfram Sang <wsa@kernel.org>, Corey Minyard <minyard@acm.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Brendan Higgins <brendan.higgins@linux.dev>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Joel Stanley <joel@jms.id.au>,
        Andrew Jeffery <andrew@aj.id.au>,
        openipmi-developer@lists.sourceforge.net,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-i2c@vger.kernel.org, openbmc@lists.ozlabs.org,
        linux-arm-kernel@lists.infradead.org,
        linux-aspeed@lists.ozlabs.org,
        Open Source Submission <patches@amperecomputing.com>
References: <20221004093106.1653317-1-quan@os.amperecomputing.com>
 <20221004093106.1653317-2-quan@os.amperecomputing.com>
 <5fbc5a54-60f2-fc0d-a4a1-839f28a4d8ba@quicinc.com>
From:   Quan Nguyen <quan@os.amperecomputing.com>
In-Reply-To: <5fbc5a54-60f2-fc0d-a4a1-839f28a4d8ba@quicinc.com>
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On 07/10/2022 20:26, Graeme Gregory wrote:
> 
> On 04/10/2022 10:31, 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 Dan for the copy_from_user() fix in the link below.
>>
>> Link: 
>> https://lore.kernel.org/linux-arm-kernel/20220310114119.13736-4-quan@os.amperecomputing.com/
>> Signed-off-by: Quan Nguyen <quan@os.amperecomputing.com>
> 
> I have been testing this on our hardware and I don't seem to be able to 
> get this driver working. I was using an older version.
> 
> I have hacked ssifbridged to deal with the change in len from u8 to 
> unsigned int.
> 
> It works as long as I only ever send SSIF commands, any attempt to read 
> a response crashes the state machine and the driver never recovers. No 
> further SSIF comms is possible! (slave doesnt even ACK writes).
> 
> A couple of comments below on possible state machine errors.
> 
> Its possible I am doing something wrong!
> 

Thanks Graeme for the test and the comments.

What's your testing hardware?

This was tested with Aspeed ast2500 and ast2600 with the patch series 
[1] below applied.

If you use the same hw, could you pick the series and see if any thing 
improve ?

[1] 
https://lore.kernel.org/all/20210616031046.2317-1-quan@os.amperecomputing.com/

>> ---
>> v10:
>>    + None
>>
>> v9:
>>    + Fix dependence with I2C subsystem                            [Randy]
>>    + Remove useless error handling path                              [CJ]
>>    + Update comment for SSIF_ABORTING state                          [CJ]
>>    + Fix "unknown type name --u8"                     [kernel test robot]
>>    + Fix ssif_bmc_remove() to return void to align with recent kernel
>>      change                                                        [Quan]
>>
>> v8:
>>    + Dropped ssif_bmc.h file and move its content to ssif_bmc.c   [Corey]
>>    + Add struct ipmi_ssif_msg to include/uapi/linux/ipmi_ssif_bmc.h
>>    header file                                                    [Corey]
>>    + Use unsigned int for len field in struct ipmi_ssif_msg       [Corey]
>>    + Avoid using packed structure                                 [Corey]
>>    + Add comment to clarify the logic flow                        [Corey]
>>    + Fix multipart read end with len=0 issue                      [Corey]
>>    + Refactor code handle the too big request message             [Corey]
>>    + Fix code indentation issue                                   [Corey]
>>    + Clean buffer before receiving request to avoid garbage        [Quan]
>>    + Fix the license to SPDX-License-Identifier: GPL-2.0-only      [Quan]
>>
>> v7:
>>    + Remove unneccessary del_timer() in response_timeout()        [Corey]
>>    + Change compatible string from "ampere,ssif-bmc" to "ssif-bmc"  [Jae]
>>    + Add MODULE_DEVICE_TABLE(of, ssif_bmc_match), fix blank line    [Jae]
>>    + Dropped the use of ssif_msg_len() macro, use the len directly [Quan]
>>    + Solve possible issue if both response timer and ssif_bmc_write()
>>    occurred at the same time                                      [Corey]
>>    + Fix wrong return type of ssif_bmc_poll()         [kernel robot test]
>>    + Refactor and introduce ssif_part_buffer struct to replace the
>>    response_buf to manage each send/receive part of ssif           [Quan]
>>    + Change SSIF_BAD_SMBUS state to SSIF_ABORTING state           [Corey]
>>    + Support abort feature to skip the current bad request/response and
>>    wait until next new request                                    [Corey]
>>    + Refactor the PEC calculation to avoid the re-calculate the PEC on
>>    each I2C_SLAVE_WRITE_RECEIVED event                             [Quan]
>>    + Fix the use of error-proned idx                              [Corey]
>>    + Defer the test for valid SMBus command until the read/write part
>>    is determined                                                   [Quan]
>>    + Change/split unsupported_smbus_cmd() to
>>    supported_[write|read]_cmd()                                   [Corey]
>>    + Abort the request if somehow its size exceeded 255 bytes      [Quan]
>>
>> 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          |  10 +
>>   drivers/char/ipmi/Makefile         |   1 +
>>   drivers/char/ipmi/ssif_bmc.c       | 873 +++++++++++++++++++++++++++++
>>   include/uapi/linux/ipmi_ssif_bmc.h |  18 +
>>   4 files changed, 902 insertions(+)
>>   create mode 100644 drivers/char/ipmi/ssif_bmc.c
>>   create mode 100644 include/uapi/linux/ipmi_ssif_bmc.h
>>
>> diff --git a/drivers/char/ipmi/Kconfig b/drivers/char/ipmi/Kconfig
>> index 39565cf74b2c..b6c0d35fc1a5 100644
>> --- a/drivers/char/ipmi/Kconfig
>> +++ b/drivers/char/ipmi/Kconfig
>> @@ -169,6 +169,16 @@ 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"
>> +    depends on I2C && 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..a7bb4b99000e
>> --- /dev/null
>> +++ b/drivers/char/ipmi/ssif_bmc.c
>> @@ -0,0 +1,873 @@
>> +// SPDX-License-Identifier: GPL-2.0-only
>> +/*
>> + * 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 <linux/ipmi_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
>> +/* Transaction includes the address, the command, the length and the 
>> PEC byte */
>> +#define MAX_TRANSACTION                         
>> (MAX_PAYLOAD_PER_TRANSACTION + 4)
>> +
>> +#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
>> +
>> +/*
>> + * 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 up to 500ms
>> + */
>> +#define RESPONSE_TIMEOUT                        500 /* ms */
>> +
>> +struct ssif_part_buffer {
>> +    u8 address;
>> +    u8 smbus_cmd;
>> +    u8 length;
>> +    u8 payload[MAX_PAYLOAD_PER_TRANSACTION];
>> +    u8 pec;
>> +    u8 index;
>> +};
>> +
>> +/*
>> + * 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_ABORTING      0x05 : Aborting state
>> + */
>> +enum ssif_state {
>> +    SSIF_READY,
>> +    SSIF_START,
>> +    SSIF_SMBUS_CMD,
>> +    SSIF_REQ_RECVING,
>> +    SSIF_RES_SENDING,
>> +    SSIF_ABORTING,
>> +    SSIF_STATE_MAX
>> +};
>> +
>> +struct ssif_bmc_ctx {
>> +    struct i2c_client       *client;
>> +    struct miscdevice       miscdev;
>> +    int                     msg_idx;
>> +    bool                    pec_support;
>> +    /* ssif bmc spinlock */
>> +    spinlock_t              lock;
>> +    wait_queue_head_t       wait_queue;
>> +    u8                      running;
>> +    enum ssif_state         state;
>> +    /* 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;
>> +    bool                    aborting;
>> +    /* Buffer for SSIF Transaction part*/
>> +    struct ssif_part_buffer part_buf;
>> +    struct ipmi_ssif_msg    response;
>> +    struct ipmi_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);
>> +}
>> +
>> +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_ABORTING:
>> +        return "SSIF_ABORTING";
>> +    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 ipmi_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,
>> +              sizeof_field(struct ipmi_ssif_msg, len) + 
>> ssif_bmc->request.len,
>> +              sizeof(struct ipmi_ssif_msg))) {
>> +        spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +        ret = -EINVAL;
>> +    } else {
>> +        count = min_t(ssize_t,
>> +                  sizeof_field(struct ipmi_ssif_msg, len) + 
>> ssif_bmc->request.len,
>> +                  sizeof(struct ipmi_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 ipmi_ssif_msg msg;
>> +    unsigned long flags;
>> +    ssize_t ret;
>> +
>> +    if (count > sizeof(struct ipmi_ssif_msg))
>> +        return -EINVAL;
>> +
>> +    if (copy_from_user(&msg, buf, count))
>> +        return -EFAULT;
>> +
>> +    if (!msg.len || count < sizeof_field(struct ipmi_ssif_msg, len) + 
>> msg.len)
>> +        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);
>> +    }
>> +
>> +    /*
>> +     * The write must complete before the response timeout fired, 
>> otherwise
>> +     * the response is aborted and wait for next request
>> +     * Return -EINVAL if the response is aborted
>> +     */
>> +    ret = (ssif_bmc->response_timer_inited) ? 0 : -EINVAL;
>> +    if (ret)
>> +        goto exit;
>> +
>> +    del_timer(&ssif_bmc->response_timer);
>> +    ssif_bmc->response_timer_inited = false;
>> +
>> +    memcpy(&ssif_bmc->response, &msg, count);
>> +    ssif_bmc->is_singlepart_read = (msg.len <= 
>> MAX_PAYLOAD_PER_TRANSACTION);
>> +
>> +    ssif_bmc->response_in_progress = true;
>> +
>> +    /* ssif_bmc not busy */
>> +    ssif_bmc->busy = false;
>> +
>> +    /* Clean old request buffer */
>> +    memset(&ssif_bmc->request, 0, sizeof(struct ipmi_ssif_msg));
>> +exit:
>> +    spin_unlock_irqrestore(&ssif_bmc->lock, flags);
>> +
>> +    return (ret < 0) ? ret : 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 __poll_t ssif_bmc_poll(struct file *file, poll_table *wait)
>> +{
>> +    struct ssif_bmc_ctx *ssif_bmc = to_ssif_bmc(file);
>> +    __poll_t 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->part_buf, 0, sizeof(struct ssif_part_buffer));
>> +    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);
>> +
>> +    /* Do nothing if the response is in progress */
>> +    if (!ssif_bmc->response_in_progress) {
>> +        /* Recover ssif_bmc from busy */
>> +        ssif_bmc->busy = false;
>> +        ssif_bmc->response_timer_inited = false;
>> +        /* Set aborting flag */
>> +        ssif_bmc->aborting = true;
>> +    }
>> +
>> +    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 ipmi_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 calculate_response_part_pec(struct ssif_part_buffer *part)
>> +{
>> +    u8 addr = part->address;
>> +
>> +    /* PEC - Start Read Address */
>> +    part->pec = i2c_smbus_pec(0, &addr, 1);
>> +    /* PEC - SSIF Command */
>> +    part->pec = i2c_smbus_pec(part->pec, &part->smbus_cmd, 1);
>> +    /* PEC - Restart Write Address */
>> +    addr = addr | 0x01;
>> +    part->pec = i2c_smbus_pec(part->pec, &addr, 1);
>> +    part->pec = i2c_smbus_pec(part->pec, &part->length, 1);
>> +    if (part->length)
>> +        part->pec = i2c_smbus_pec(part->pec, part->payload, 
>> part->length);
>> +}
>> +
>> +static void set_singlepart_response_buffer(struct ssif_bmc_ctx 
>> *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +
>> +    part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +    part->length = (u8)ssif_bmc->response.len;
>> +
>> +    /* Clear the rest to 0 */
>> +    memset(part->payload + part->length, 0, 
>> MAX_PAYLOAD_PER_TRANSACTION - part->length);
>> +    memcpy(&part->payload[0], &ssif_bmc->response.payload[0], 
>> part->length);
>> +}
>> +
>> +static void set_multipart_response_buffer(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +    u8 part_len = 0;
>> +
>> +    part->address = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +    switch (part->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.
>> +         */
>> +        ssif_bmc->nbytes_processed = 0;
>> +        ssif_bmc->block_num = 0;
>> +        part->length = MAX_PAYLOAD_PER_TRANSACTION;
>> +        part_len = MAX_IPMI_DATA_PER_START_TRANSACTION;
>> +        ssif_bmc->remain_len = ssif_bmc->response.len - part_len;
>> +
>> +        part->payload[0] = 0x00; /* Start Flag */
>> +        part->payload[1] = 0x01; /* Start Flag */
>> +
>> +        memcpy(&part->payload[2], &ssif_bmc->response.payload[0], 
>> part_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
>> +             *
>> +             */
>> +            /* Clean the buffer */
>> +            memset(&part->payload[0], 0, MAX_PAYLOAD_PER_TRANSACTION);
>> +            part->length = ssif_bmc->remain_len + 1;
>> +            part_len = ssif_bmc->remain_len;
>> +            ssif_bmc->block_num = 0xFF;
>> +            part->payload[0] = ssif_bmc->block_num;
>> +        } 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
>> +             */
>> +            part->length = MAX_PAYLOAD_PER_TRANSACTION;
>> +            part_len = MAX_IPMI_DATA_PER_MIDDLE_TRANSACTION;
>> +            part->payload[0] = ssif_bmc->block_num;
>> +            ssif_bmc->block_num++;
>> +        }
>> +
>> +        ssif_bmc->remain_len -= part_len;
>> +        memcpy(&part->payload[1], ssif_bmc->response.payload + 
>> ssif_bmc->nbytes_processed,
>> +               part_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__, part->smbus_cmd);
>> +        break;
>> +    }
>> +
>> +    ssif_bmc->nbytes_processed += part_len;
>> +}
>> +
>> +static bool supported_read_cmd(u8 cmd)
>> +{
>> +    if (cmd == SSIF_IPMI_SINGLEPART_READ ||
>> +        cmd == SSIF_IPMI_MULTIPART_READ_START ||
>> +        cmd == SSIF_IPMI_MULTIPART_READ_MIDDLE)
>> +        return true;
>> +
>> +    return false;
>> +}
>> +
>> +static bool supported_write_cmd(u8 cmd)
>> +{
>> +    if (cmd == SSIF_IPMI_SINGLEPART_WRITE ||
>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_START ||
>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_MIDDLE ||
>> +        cmd == SSIF_IPMI_MULTIPART_WRITE_END)
>> +        return true;
>> +
>> +    return false;
>> +}
>> +
>> +/* Process the IPMI response that will be read by master */
>> +static void handle_read_processed(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +
>> +    /* msg_idx start from 0 */
>> +    if (part->index < part->length)
>> +        *val = part->payload[part->index];
>> +    else if (part->index == part->length && ssif_bmc->pec_support)
>> +        *val = part->pec;
>> +    else
>> +        *val = 0;
>> +
>> +    part->index++;
>> +}
>> +
>> +static void handle_write_received(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    /*
>> +     * The msg_idx must be 1 when first enter SSIF_REQ_RECVING state
>> +     * And it would never exceeded 36 bytes included the 32 bytes max 
>> payload +
>> +     * the address + the command + the len and the PEC.
>> +     */
>> +    if (ssif_bmc->msg_idx < 1  || ssif_bmc->msg_idx > MAX_TRANSACTION)
>> +        return;
>> +
>> +    if (ssif_bmc->msg_idx == 1) {
>> +        ssif_bmc->part_buf.length = *val;
>> +        ssif_bmc->part_buf.index = 0;
>> +    } else {
>> +        ssif_bmc->part_buf.payload[ssif_bmc->part_buf.index++] = *val;
>> +    }
>> +
>> +    ssif_bmc->msg_idx++;
>> +}
>> +
>> +static bool validate_request_part(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +    bool ret = true;
>> +    u8 cpec;
>> +    u8 addr;
>> +
>> +    if (part->index == part->length) {
>> +        /* PEC is not included */
>> +        ssif_bmc->pec_support = false;
>> +        ret = true;
>> +        goto exit;
>> +    }
>> +
>> +    if (part->index != part->length + 1) {
>> +        ret = false;
>> +        goto exit;
>> +    }
>> +
>> +    /* PEC is included */
>> +    ssif_bmc->pec_support = true;
>> +    part->pec = part->payload[part->length];
>> +    addr = GET_8BIT_ADDR(ssif_bmc->client->addr);
>> +    cpec = i2c_smbus_pec(0, &addr, 1);
>> +    cpec = i2c_smbus_pec(cpec, &part->smbus_cmd, 1);
>> +    cpec = i2c_smbus_pec(cpec, &part->length, 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 (part->length)
>> +        cpec = i2c_smbus_pec(cpec, part->payload, part->length);
>> +
>> +    if (cpec != part->pec)
>> +        ret = false;
>> +
>> +exit:
>> +    return ret;
>> +}
>> +
>> +static void process_request_part(struct ssif_bmc_ctx *ssif_bmc)
>> +{
>> +    struct ssif_part_buffer *part = &ssif_bmc->part_buf;
>> +    unsigned int len;
>> +
>> +    switch (part->smbus_cmd) {
>> +    case SSIF_IPMI_SINGLEPART_WRITE:
>> +        /* save the whole part to request*/
>> +        ssif_bmc->request.len = part->length;
>> +        memcpy(ssif_bmc->request.payload, part->payload, part->length);
>> +
>> +        break;
>> +    case SSIF_IPMI_MULTIPART_WRITE_START:
>> +        ssif_bmc->request.len = 0;
>> +
>> +        fallthrough;
>> +    case SSIF_IPMI_MULTIPART_WRITE_MIDDLE:
>> +    case SSIF_IPMI_MULTIPART_WRITE_END:
>> +        len = ssif_bmc->request.len + part->length;
>> +        /* Do the bound check here, not allow the request len exceed 
>> 254 bytes */
>> +        if (len > IPMI_SSIF_PAYLOAD_MAX) {
>> +            dev_warn(&ssif_bmc->client->dev,
>> +                 "Warn: Request exceeded 254 bytes, aborting");
>> +            /* Request too long, aborting */
>> +            ssif_bmc->aborting =  true;
>> +        } else {
>> +            memcpy(ssif_bmc->request.payload + ssif_bmc->request.len,
>> +                   part->payload, part->length);
>> +            ssif_bmc->request.len += part->length;
>> +        }
>> +        break;
>> +    default:
>> +        /* Do not expect to go to this case */
>> +        dev_err(&ssif_bmc->client->dev, "%s: Unexpected SMBus command 
>> 0x%x\n",
>> +            __func__, part->smbus_cmd);
>> +        break;
>> +    }
>> +}
>> +
>> +static void process_smbus_cmd(struct ssif_bmc_ctx *ssif_bmc, u8 *val)
>> +{
>> +    /* SMBUS command can vary (single or multi-part) */
>> +    ssif_bmc->part_buf.smbus_cmd = *val;
>> +    ssif_bmc->msg_idx = 1;
>> +    memset(&ssif_bmc->part_buf.payload[0], 0, 
>> MAX_PAYLOAD_PER_TRANSACTION);
>> +
>> +    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);
>> +
>> +        /* This is new request, flip aborting flag if set */
>> +        if (ssif_bmc->aborting)
>> +            ssif_bmc->aborting = false;
>> +    }
>> +}
>> +
>> +static void on_read_requested_event(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY ||
> Is this actually correct? The state machine seems to set this as the 
> default state and in my testing we seem to always reach here with the 
> state == SSIF_READY?

The I2C_SLAVE_READ_REQUESTED event is expected to come on SSIF_SMBUS_CMD 
state where Slave has already received and validated the SMBus command, 
in this case is the I2C_SLAVE_READ_REQUESTED event if the SMBus command 
indeed is the READ command. You can see the check supported_read_cmd() 
below.

If Slave see the I2C_SLAVE_READ_REQUESTED event on other states, it will 
transition to SSIF_ABORTING state that discard everything until there is 
a new transaction come.

On READ, the sequence of Slave event should be as below:
I2C_SLAVE_WRITE_REQUESTED (addr) => I2C_SLAVE_WRITE_RECEIVED (SMBus cmd) 
=> I2C_SLAVE_READ_REQUESTED (Slave feed the first byte) => 
I2C_SLAVE_READ_PROCESSED (Slave 2nd byte) => .... => I2C_SLAVE_STOP

>> +        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 READ REQUESTED in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
>> +        ssif_bmc->state = SSIF_ABORTING;
>> +        *val = 0;
>> +        return;
>> +
>> +    } else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +        if (!supported_read_cmd(ssif_bmc->part_buf.smbus_cmd)) {
>> +            dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus 
>> read command=0x%x",
>> +                 ssif_bmc->part_buf.smbus_cmd);
>> +            ssif_bmc->aborting = true;
>> +        }
>> +
>> +        if (ssif_bmc->aborting)
>> +            ssif_bmc->state = SSIF_ABORTING;
>> +        else
>> +            ssif_bmc->state = SSIF_RES_SENDING;
>> +    }
>> +
>> +    ssif_bmc->msg_idx = 0;
>> +
>> +    /* Send 0 if there is nothing to send */
>> +    if (!ssif_bmc->response_in_progress || ssif_bmc->state == 
>> SSIF_ABORTING) {
>> +        *val = 0;
>> +        return;
>> +    }
>> +
>> +    if (ssif_bmc->is_singlepart_read)
>> +        set_singlepart_response_buffer(ssif_bmc);
>> +    else
>> +        set_multipart_response_buffer(ssif_bmc);
>> +
>> +    calculate_response_part_pec(&ssif_bmc->part_buf);
>> +    ssif_bmc->part_buf.index = 0;
>> +    *val = ssif_bmc->part_buf.length;
>> +}
>> +
>> +static void on_read_processed_event(struct ssif_bmc_ctx *ssif_bmc, u8 
>> *val)
>> +{
>> +    if (ssif_bmc->state == SSIF_READY ||
> Same comment as above?

Same here, I2C_SLAVE_READ_PROCESSED is expected to come after the 
I2C_SLAVE_READ_REQUESTED or other I2C_SLAVE_READ_PROCESSED. ie: when the 
state is SSIF_RES_SENDING.
If it comes when Slave in states other than SSIF_RES_SENDING, the Slave 
will transition to SSIF_ABORTING state.

>> +        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_ABORTING;
>> +        *val = 0;
>> +        return;
>> +    }
>> +
>> +    /* Send 0 if there is nothing to send */
>> +    if (!ssif_bmc->response_in_progress || ssif_bmc->state == 
>> SSIF_ABORTING) {
>> +        *val = 0;
>> +        return;
>> +    }
>> +
>> +    handle_read_processed(ssif_bmc, val);
>> +}
>> +
>> +static void on_write_requested_event(struct ssif_bmc_ctx *ssif_bmc, 
>> u8 *val)
>> +{
>> +    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_ABORTING;
>> +        return;
>> +    }
>> +
>> +    ssif_bmc->msg_idx = 0;
>> +    ssif_bmc->part_buf.address = *val;
>> +}
>> +
>> +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_ABORTING;
>> +
>> +    } else if (ssif_bmc->state == SSIF_START) {
>> +        ssif_bmc->state = SSIF_SMBUS_CMD;
>> +
>> +    } else if (ssif_bmc->state == SSIF_SMBUS_CMD) {
>> +        if (!supported_write_cmd(ssif_bmc->part_buf.smbus_cmd)) {
>> +            dev_warn(&ssif_bmc->client->dev, "Warn: Unknown SMBus 
>> write command=0x%x",
>> +                 ssif_bmc->part_buf.smbus_cmd);
>> +            ssif_bmc->aborting = true;
>> +        }
>> +
>> +        if (ssif_bmc->aborting)
>> +            ssif_bmc->state = SSIF_ABORTING;
>> +        else
>> +            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 ||
>> +        ssif_bmc->state == SSIF_ABORTING) {
>> +        dev_warn(&ssif_bmc->client->dev,
>> +             "Warn: %s unexpected SLAVE STOP in state=%s\n",
>> +             __func__, state_to_string(ssif_bmc->state));
>> +        ssif_bmc->state = SSIF_READY;
>> +
>> +    } else if (ssif_bmc->state == SSIF_REQ_RECVING) {
>> +        if (validate_request_part(ssif_bmc)) {
>> +            process_request_part(ssif_bmc);
>> +            if (ssif_bmc->part_buf.smbus_cmd == 
>> SSIF_IPMI_SINGLEPART_WRITE ||
>> +                ssif_bmc->part_buf.smbus_cmd == 
>> SSIF_IPMI_MULTIPART_WRITE_END)
>> +                handle_request(ssif_bmc);
>> +            ssif_bmc->state = SSIF_READY;
>> +        } else {
>> +            /*
>> +             * 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
>> +             */
>> +            dev_err(&ssif_bmc->client->dev, "Error: invalid pec\n");
>> +            ssif_bmc->aborting = true;
>> +        }
>> +    } else if (ssif_bmc->state == SSIF_RES_SENDING) {
>> +        if (ssif_bmc->is_singlepart_read || ssif_bmc->block_num == 0xFF)
>> +            /* Invalidate response buffer to denote it is sent */
>> +            complete_response(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 :
>> +        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->aborting && 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)
>> +        return ret;
>> +
>> +    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);
>> +
>> +    return ret;
>> +}
>> +
>> +static void 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);
>> +}
>> +
>> +static const struct of_device_id ssif_bmc_match[] = {
>> +    { .compatible = "ssif-bmc" },
>> +    { },
>> +};
>> +MODULE_DEVICE_TABLE(of, ssif_bmc_match);
>> +
>> +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 <quan@os.amperecomputing.com>");
>> +MODULE_AUTHOR("Chuong Tran <chuong@os.amperecomputing.com>");
>> +MODULE_DESCRIPTION("Linux device driver of the BMC IPMI SSIF 
>> interface.");
>> +MODULE_LICENSE("GPL");
>> diff --git a/include/uapi/linux/ipmi_ssif_bmc.h 
>> b/include/uapi/linux/ipmi_ssif_bmc.h
>> new file mode 100644
>> index 000000000000..1c6a753dad08
>> --- /dev/null
>> +++ b/include/uapi/linux/ipmi_ssif_bmc.h
>> @@ -0,0 +1,18 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only WITH Linux-syscall-note*/
>> +/*
>> + * Copyright (c) 2022, Ampere Computing LLC.
>> + */
>> +
>> +#ifndef _UAPI_LINUX_IPMI_SSIF_BMC_H
>> +#define _UAPI_LINUX_IPMI_SSIF_BMC_H
>> +
>> +#include <linux/types.h>
>> +
>> +/* Max length of ipmi ssif message included netfn and cmd field */
>> +#define IPMI_SSIF_PAYLOAD_MAX         254
>> +struct ipmi_ssif_msg {
>> +    unsigned int len;
>> +    __u8    payload[IPMI_SSIF_PAYLOAD_MAX];
>> +};
>> +
>> +#endif /* _UAPI_LINUX_IPMI_SSIF_BMC_H */