/*
    i2c-stub.c - I2C/SMBus chip emulator

    Copyright (c) 2004 Mark M. Hoffman <mhoffman@lightlink.com>
    Copyright (C) 2007, 2012 Jean Delvare <jdelvare@suse.de>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#define DEBUG 1

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

#define MAX_CHIPS 10
#define STUB_FUNC (I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE | \
                   I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA | \
                   I2C_FUNC_SMBUS_I2C_BLOCK)

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;
module_param(functionality, ulong, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(functionality, "Override functionality bitfield");

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

static struct stub_chip *stub_chips;

/* 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;

        /* Search for the right chip */
        for (i = 0; i < MAX_CHIPS && chip_addr[i]; 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 {
                        data->byte = chip->words[chip->pointer++] & 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:
                if (read_write == I2C_SMBUS_WRITE) {
                        chip->words[command] &= 0xff00;
                        chip->words[command] |= data->byte;
                        dev_dbg(&adap->dev,
                                "smbus byte data - addr 0x%02x, wrote 0x%02x at 0x%02x.\n",
                                addr, data->byte, command);
                } else {
                        data->byte = chip->words[command] & 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:
                if (read_write == I2C_SMBUS_WRITE) {
                        chip->words[command] = 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 = chip->words[command];
                        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:
                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;

        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 & 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_init(void)
{
        int i, ret;

        if (!chip_addr[0]) {
                pr_err("i2c-stub: 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("i2c-stub: Invalid chip address 0x%02x\n",
                               chip_addr[i]);
                        return -EINVAL;
                }

                pr_info("i2c-stub: Virtual chip at 0x%02x\n", chip_addr[i]);
        }

        /* Allocate memory for all chips at once */
        stub_chips = kzalloc(i * sizeof(struct stub_chip), GFP_KERNEL);
        if (!stub_chips) {
                pr_err("i2c-stub: Out of memory\n");
                return -ENOMEM;
        }

        ret = i2c_add_adapter(&stub_adapter);
        if (ret)
                kfree(stub_chips);
        return ret;
}

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

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);