// SPDX-License-Identifier: GPL-2.0-or-later
/*
    i2c-stub.c - I2C/SMBus chip emulator

    Copyright (c) 2004 Mark M. Hoffman <mhoffman@lightlink.com>
    Copyright (C) 2007-2014 Jean Delvare <jdelvare@suse.de>

*/

#define DEBUG 1
#define pr_fmt(fmt) "i2c-stub: " fmt

#include <linux/errno.h>
#include <linux/i2c.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/slab.h>

#define MAX_CHIPS 10

/*
 * Support for I2C_FUNC_SMBUS_BLOCK_DATA is disabled by default and must
 * be enabled explicitly by setting the I2C_FUNC_SMBUS_BLOCK_DATA bits
 * in the 'functionality' module parameter.
 */
#define STUB_FUNC_DEFAULT \
                (I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE | \
                 I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA | \
                 I2C_FUNC_SMBUS_I2C_BLOCK)

#define STUB_FUNC_ALL \
                (STUB_FUNC_DEFAULT | I2C_FUNC_SMBUS_BLOCK_DATA)

static unsigned short chip_addr[MAX_CHIPS];
module_param_array(chip_addr, ushort, NULL, S_IRUGO);
MODULE_PARM_DESC(chip_addr,
                 "Chip addresses (up to 10, between 0x03 and 0x77)");

static unsigned long functionality = STUB_FUNC_DEFAULT;
module_param(functionality, ulong, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(functionality, "Override functionality bitfield");

/* Some chips have banked register ranges */

static u8 bank_reg[MAX_CHIPS];
module_param_array(bank_reg, byte, NULL, S_IRUGO);
MODULE_PARM_DESC(bank_reg, "Bank register");

static u8 bank_mask[MAX_CHIPS];
module_param_array(bank_mask, byte, NULL, S_IRUGO);
MODULE_PARM_DESC(bank_mask, "Bank value mask");

static u8 bank_start[MAX_CHIPS];
module_param_array(bank_start, byte, NULL, S_IRUGO);
MODULE_PARM_DESC(bank_start, "First banked register");

static u8 bank_end[MAX_CHIPS];
module_param_array(bank_end, byte, NULL, S_IRUGO);
MODULE_PARM_DESC(bank_end, "Last banked register");

struct smbus_block_data {
        struct list_head node;
        u8 command;
        u8 len;
        u8 block[I2C_SMBUS_BLOCK_MAX];
};

struct stub_chip {
        u8 pointer;
        u16 words[256];         /* Byte operations use the LSB as per SMBus
                                   specification */
        struct list_head smbus_blocks;

        /* For chips with banks, extra registers are allocated dynamically */
        u8 bank_reg;
        u8 bank_shift;
        u8 bank_mask;
        u8 bank_sel;            /* Currently selected bank */
        u8 bank_start;
        u8 bank_end;
        u16 bank_size;
        u16 *bank_words;        /* Room for bank_mask * bank_size registers */
};

static struct stub_chip *stub_chips;
static int stub_chips_nr;

static struct smbus_block_data *stub_find_block(struct device *dev,
                                                struct stub_chip *chip,
                                                u8 command, bool create)
{
        struct smbus_block_data *b, *rb = NULL;

        list_for_each_entry(b, &chip->smbus_blocks, node) {
                if (b->command == command) {
                        rb = b;
                        break;
                }
        }
        if (rb == NULL && create) {
                rb = devm_kzalloc(dev, sizeof(*rb), GFP_KERNEL);
                if (rb == NULL)
                        return rb;
                rb->command = command;
                list_add(&rb->node, &chip->smbus_blocks);
        }
        return rb;
}

static u16 *stub_get_wordp(struct stub_chip *chip, u8 offset)
{
        if (chip->bank_sel &&
            offset >= chip->bank_start && offset <= chip->bank_end)
                return chip->bank_words +
                       (chip->bank_sel - 1) * chip->bank_size +
                       offset - chip->bank_start;
        else
                return chip->words + offset;
}

/* Return negative errno on error. */
static s32 stub_xfer(struct i2c_adapter *adap, u16 addr, unsigned short flags,
        char read_write, u8 command, int size, union i2c_smbus_data *data)
{
        s32 ret;
        int i, len;
        struct stub_chip *chip = NULL;
        struct smbus_block_data *b;
        u16 *wordp;

        /* Search for the right chip */
        for (i = 0; i < stub_chips_nr; i++) {
                if (addr == chip_addr[i]) {
                        chip = stub_chips + i;
                        break;
                }
        }
        if (!chip)
                return -ENODEV;

        switch (size) {

        case I2C_SMBUS_QUICK:
                dev_dbg(&adap->dev, "smbus quick - addr 0x%02x\n", addr);
                ret = 0;
                break;

        case I2C_SMBUS_BYTE:
                if (read_write == I2C_SMBUS_WRITE) {
                        chip->pointer = command;
                        dev_dbg(&adap->dev,
                                "smbus byte - addr 0x%02x, wrote 0x%02x.\n",
                                addr, command);
                } else {
                        wordp = stub_get_wordp(chip, chip->pointer++);
                        data->byte = *wordp & 0xff;
                        dev_dbg(&adap->dev,
                                "smbus byte - addr 0x%02x, read  0x%02x.\n",
                                addr, data->byte);
                }

                ret = 0;
                break;

        case I2C_SMBUS_BYTE_DATA:
                wordp = stub_get_wordp(chip, command);
                if (read_write == I2C_SMBUS_WRITE) {
                        *wordp &= 0xff00;
                        *wordp |= data->byte;
                        dev_dbg(&adap->dev,
                                "smbus byte data - addr 0x%02x, wrote 0x%02x at 0x%02x.\n",
                                addr, data->byte, command);

                        /* Set the bank as needed */
                        if (chip->bank_words && command == chip->bank_reg) {
                                chip->bank_sel =
                                        (data->byte >> chip->bank_shift)
                                        & chip->bank_mask;
                                dev_dbg(&adap->dev,
                                        "switching to bank %u.\n",
                                        chip->bank_sel);
                        }
                } else {
                        data->byte = *wordp & 0xff;
                        dev_dbg(&adap->dev,
                                "smbus byte data - addr 0x%02x, read  0x%02x at 0x%02x.\n",
                                addr, data->byte, command);
                }
                chip->pointer = command + 1;

                ret = 0;
                break;

        case I2C_SMBUS_WORD_DATA:
                wordp = stub_get_wordp(chip, command);
                if (read_write == I2C_SMBUS_WRITE) {
                        *wordp = data->word;
                        dev_dbg(&adap->dev,
                                "smbus word data - addr 0x%02x, wrote 0x%04x at 0x%02x.\n",
                                addr, data->word, command);
                } else {
                        data->word = *wordp;
                        dev_dbg(&adap->dev,
                                "smbus word data - addr 0x%02x, read  0x%04x at 0x%02x.\n",
                                addr, data->word, command);
                }

                ret = 0;
                break;

        case I2C_SMBUS_I2C_BLOCK_DATA:
                /*
                 * We ignore banks here, because banked chips don't use I2C
                 * block transfers
                 */
                if (data->block[0] > 256 - command)     /* Avoid overrun */
                        data->block[0] = 256 - command;
                len = data->block[0];
                if (read_write == I2C_SMBUS_WRITE) {
                        for (i = 0; i < len; i++) {
                                chip->words[command + i] &= 0xff00;
                                chip->words[command + i] |= data->block[1 + i];
                        }
                        dev_dbg(&adap->dev,
                                "i2c block data - addr 0x%02x, wrote %d bytes at 0x%02x.\n",
                                addr, len, command);
                } else {
                        for (i = 0; i < len; i++) {
                                data->block[1 + i] =
                                        chip->words[command + i] & 0xff;
                        }
                        dev_dbg(&adap->dev,
                                "i2c block data - addr 0x%02x, read  %d bytes at 0x%02x.\n",
                                addr, len, command);
                }

                ret = 0;
                break;

        case I2C_SMBUS_BLOCK_DATA:
                /*
                 * We ignore banks here, because chips typically don't use both
                 * banks and SMBus block transfers
                 */
                b = stub_find_block(&adap->dev, chip, command, false);
                if (read_write == I2C_SMBUS_WRITE) {
                        len = data->block[0];
                        if (len == 0 || len > I2C_SMBUS_BLOCK_MAX) {
                                ret = -EINVAL;
                                break;
                        }
                        if (b == NULL) {
                                b = stub_find_block(&adap->dev, chip, command,
                                                    true);
                                if (b == NULL) {
                                        ret = -ENOMEM;
                                        break;
                                }
                        }
                        /* Largest write sets read block length */
                        if (len > b->len)
                                b->len = len;
                        for (i = 0; i < len; i++)
                                b->block[i] = data->block[i + 1];
                        /* update for byte and word commands */
                        chip->words[command] = (b->block[0] << 8) | b->len;
                        dev_dbg(&adap->dev,
                                "smbus block data - addr 0x%02x, wrote %d bytes at 0x%02x.\n",
                                addr, len, command);
                } else {
                        if (b == NULL) {
                                dev_dbg(&adap->dev,
                                        "SMBus block read command without prior block write not supported\n");
                                ret = -EOPNOTSUPP;
                                break;
                        }
                        len = b->len;
                        data->block[0] = len;
                        for (i = 0; i < len; i++)
                                data->block[i + 1] = b->block[i];
                        dev_dbg(&adap->dev,
                                "smbus block data - addr 0x%02x, read  %d bytes at 0x%02x.\n",
                                addr, len, command);
                }

                ret = 0;
                break;

        default:
                dev_dbg(&adap->dev, "Unsupported I2C/SMBus command\n");
                ret = -EOPNOTSUPP;
                break;
        } /* switch (size) */

        return ret;
}

static u32 stub_func(struct i2c_adapter *adapter)
{
        return STUB_FUNC_ALL & functionality;
}

static const struct i2c_algorithm smbus_algorithm = {
        .functionality  = stub_func,
        .smbus_xfer     = stub_xfer,
};

static struct i2c_adapter stub_adapter = {
        .owner          = THIS_MODULE,
        .class          = I2C_CLASS_HWMON | I2C_CLASS_SPD,
        .algo           = &smbus_algorithm,
        .name           = "SMBus stub driver",
};

static int __init i2c_stub_allocate_banks(int i)
{
        struct stub_chip *chip = stub_chips + i;

        chip->bank_reg = bank_reg[i];
        chip->bank_start = bank_start[i];
        chip->bank_end = bank_end[i];
        chip->bank_size = bank_end[i] - bank_start[i] + 1;

        /* We assume that all bits in the mask are contiguous */
        chip->bank_mask = bank_mask[i];
        while (!(chip->bank_mask & 1)) {
                chip->bank_shift++;
                chip->bank_mask >>= 1;
        }

        chip->bank_words = kcalloc(chip->bank_mask * chip->bank_size,
                                   sizeof(u16),
                                   GFP_KERNEL);
        if (!chip->bank_words)
                return -ENOMEM;

        pr_debug("Allocated %u banks of %u words each (registers 0x%02x to 0x%02x)\n",
                 chip->bank_mask, chip->bank_size, chip->bank_start,
                 chip->bank_end);

        return 0;
}

static void i2c_stub_free(void)
{
        int i;

        for (i = 0; i < stub_chips_nr; i++)
                kfree(stub_chips[i].bank_words);
        kfree(stub_chips);
}

static int __init i2c_stub_init(void)
{
        int i, ret;

        if (!chip_addr[0]) {
                pr_err("Please specify a chip address\n");
                return -ENODEV;
        }

        for (i = 0; i < MAX_CHIPS && chip_addr[i]; i++) {
                if (chip_addr[i] < 0x03 || chip_addr[i] > 0x77) {
                        pr_err("Invalid chip address 0x%02x\n",
                               chip_addr[i]);
                        return -EINVAL;
                }

                pr_info("Virtual chip at 0x%02x\n", chip_addr[i]);
        }

        /* Allocate memory for all chips at once */
        stub_chips_nr = i;
        stub_chips = kcalloc(stub_chips_nr, sizeof(struct stub_chip),
                             GFP_KERNEL);
        if (!stub_chips)
                return -ENOMEM;

        for (i = 0; i < stub_chips_nr; i++) {
                INIT_LIST_HEAD(&stub_chips[i].smbus_blocks);

                /* Allocate extra memory for banked register ranges */
                if (bank_mask[i]) {
                        ret = i2c_stub_allocate_banks(i);
                        if (ret)
                                goto fail_free;
                }
        }

        ret = i2c_add_adapter(&stub_adapter);
        if (ret)
                goto fail_free;

        return 0;

 fail_free:
        i2c_stub_free();
        return ret;
}

static void __exit i2c_stub_exit(void)
{
        i2c_del_adapter(&stub_adapter);
        i2c_stub_free();
}

MODULE_AUTHOR("Mark M. Hoffman <mhoffman@lightlink.com>");
MODULE_DESCRIPTION("I2C stub driver");
MODULE_LICENSE("GPL");

module_init(i2c_stub_init);
module_exit(i2c_stub_exit);