Re: [PATCH v10 1/3] ipmi: ssif_bmc: Add SSIF BMC driver

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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@xxxxxxxxxxxxxxxxxxxxxx/
Signed-off-by: Quan Nguyen <quan@xxxxxxxxxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxxxx/

---
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@xxxxxxxxxxxxxxxxxxxxxx>");
+MODULE_AUTHOR("Chuong Tran <chuong@xxxxxxxxxxxxxxxxxxxxxx>");
+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 */



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