// 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(msg.len) ||
            count > sizeof(struct ipmi_ssif_msg))
                return -EINVAL;

        if (copy_from_user(&msg, buf, count))
                return -EFAULT;

        if (!msg.len || msg.len > IPMI_SSIF_PAYLOAD_MAX ||
            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;

        timer_delete(&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 |= EPOLLIN;

        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;
        wake_up_all(&ssif_bmc->wait_queue);
}

static void response_timeout(struct timer_list *t)
{
        struct ssif_bmc_ctx *ssif_bmc = timer_container_of(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 ||
            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 ||
            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) {
                        memset(&ssif_bmc->part_buf, 0, sizeof(struct ssif_part_buffer));
                        /* 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 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->aborting && ssif_bmc->busy)
                ret = -EBUSY;

        spin_unlock_irqrestore(&ssif_bmc->lock, flags);

        return ret;
}

static int ssif_bmc_probe(struct i2c_client *client)
{
        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 },
        { }
};
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");