/*
 * at24.c - handle most I2C EEPROMs
 *
 * Copyright (C) 2005-2007 David Brownell
 * Copyright (C) 2008 Wolfram Sang, Pengutronix
 *
 * 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.
 */
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/mutex.h>
#include <linux/mod_devicetable.h>
#include <linux/log2.h>
#include <linux/bitops.h>
#include <linux/jiffies.h>
#include <linux/of.h>
#include <linux/acpi.h>
#include <linux/i2c.h>
#include <linux/nvmem-provider.h>
#include <linux/platform_data/at24.h>

/*
 * I2C EEPROMs from most vendors are inexpensive and mostly interchangeable.
 * Differences between different vendor product lines (like Atmel AT24C or
 * MicroChip 24LC, etc) won't much matter for typical read/write access.
 * There are also I2C RAM chips, likewise interchangeable. One example
 * would be the PCF8570, which acts like a 24c02 EEPROM (256 bytes).
 *
 * However, misconfiguration can lose data. "Set 16-bit memory address"
 * to a part with 8-bit addressing will overwrite data. Writing with too
 * big a page size also loses data. And it's not safe to assume that the
 * conventional addresses 0x50..0x57 only hold eeproms; a PCF8563 RTC
 * uses 0x51, for just one example.
 *
 * Accordingly, explicit board-specific configuration data should be used
 * in almost all cases. (One partial exception is an SMBus used to access
 * "SPD" data for DRAM sticks. Those only use 24c02 EEPROMs.)
 *
 * So this driver uses "new style" I2C driver binding, expecting to be
 * told what devices exist. That may be in arch/X/mach-Y/board-Z.c or
 * similar kernel-resident tables; or, configuration data coming from
 * a bootloader.
 *
 * Other than binding model, current differences from "eeprom" driver are
 * that this one handles write access and isn't restricted to 24c02 devices.
 * It also handles larger devices (32 kbit and up) with two-byte addresses,
 * which won't work on pure SMBus systems.
 */

struct at24_data {
        struct at24_platform_data chip;
        int use_smbus;
        int use_smbus_write;

        ssize_t (*read_func)(struct at24_data *, char *, unsigned int, size_t);
        ssize_t (*write_func)(struct at24_data *,
                              const char *, unsigned int, size_t);

        /*
         * Lock protects against activities from other Linux tasks,
         * but not from changes by other I2C masters.
         */
        struct mutex lock;

        u8 *writebuf;
        unsigned write_max;
        unsigned num_addresses;

        struct nvmem_config nvmem_config;
        struct nvmem_device *nvmem;

        /*
         * Some chips tie up multiple I2C addresses; dummy devices reserve
         * them for us, and we'll use them with SMBus calls.
         */
        struct i2c_client *client[];
};

/*
 * This parameter is to help this driver avoid blocking other drivers out
 * of I2C for potentially troublesome amounts of time. With a 100 kHz I2C
 * clock, one 256 byte read takes about 1/43 second which is excessive;
 * but the 1/170 second it takes at 400 kHz may be quite reasonable; and
 * at 1 MHz (Fm+) a 1/430 second delay could easily be invisible.
 *
 * This value is forced to be a power of two so that writes align on pages.
 */
static unsigned io_limit = 128;
module_param(io_limit, uint, 0);
MODULE_PARM_DESC(io_limit, "Maximum bytes per I/O (default 128)");

/*
 * Specs often allow 5 msec for a page write, sometimes 20 msec;
 * it's important to recover from write timeouts.
 */
static unsigned write_timeout = 25;
module_param(write_timeout, uint, 0);
MODULE_PARM_DESC(write_timeout, "Time (in ms) to try writes (default 25)");

#define AT24_SIZE_BYTELEN 5
#define AT24_SIZE_FLAGS 8

#define AT24_BITMASK(x) (BIT(x) - 1)

/* create non-zero magic value for given eeprom parameters */
#define AT24_DEVICE_MAGIC(_len, _flags)                 \
        ((1 << AT24_SIZE_FLAGS | (_flags))              \
            << AT24_SIZE_BYTELEN | ilog2(_len))

/*
 * Both reads and writes fail if the previous write didn't complete yet. This
 * macro loops a few times waiting at least long enough for one entire page
 * write to work while making sure that at least one iteration is run before
 * checking the break condition.
 *
 * It takes two parameters: a variable in which the future timeout in jiffies
 * will be stored and a temporary variable holding the time of the last
 * iteration of processing the request. Both should be unsigned integers
 * holding at least 32 bits.
 */
#define loop_until_timeout(tout, op_time)                               \
        for (tout = jiffies + msecs_to_jiffies(write_timeout), op_time = 0; \
             op_time ? time_before(op_time, tout) : true;               \
             usleep_range(1000, 1500), op_time = jiffies)

static const struct i2c_device_id at24_ids[] = {
        /* needs 8 addresses as A0-A2 are ignored */
        { "24c00",      AT24_DEVICE_MAGIC(128 / 8,      AT24_FLAG_TAKE8ADDR) },
        /* old variants can't be handled with this generic entry! */
        { "24c01",      AT24_DEVICE_MAGIC(1024 / 8,     0) },
        { "24cs01",     AT24_DEVICE_MAGIC(16,
                                AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
        { "24c02",      AT24_DEVICE_MAGIC(2048 / 8,     0) },
        { "24cs02",     AT24_DEVICE_MAGIC(16,
                                AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
        { "24mac402",   AT24_DEVICE_MAGIC(48 / 8,
                                AT24_FLAG_MAC | AT24_FLAG_READONLY) },
        { "24mac602",   AT24_DEVICE_MAGIC(64 / 8,
                                AT24_FLAG_MAC | AT24_FLAG_READONLY) },
        /* spd is a 24c02 in memory DIMMs */
        { "spd",        AT24_DEVICE_MAGIC(2048 / 8,
                                AT24_FLAG_READONLY | AT24_FLAG_IRUGO) },
        { "24c04",      AT24_DEVICE_MAGIC(4096 / 8,     0) },
        { "24cs04",     AT24_DEVICE_MAGIC(16,
                                AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
        /* 24rf08 quirk is handled at i2c-core */
        { "24c08",      AT24_DEVICE_MAGIC(8192 / 8,     0) },
        { "24cs08",     AT24_DEVICE_MAGIC(16,
                                AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
        { "24c16",      AT24_DEVICE_MAGIC(16384 / 8,    0) },
        { "24cs16",     AT24_DEVICE_MAGIC(16,
                                AT24_FLAG_SERIAL | AT24_FLAG_READONLY) },
        { "24c32",      AT24_DEVICE_MAGIC(32768 / 8,    AT24_FLAG_ADDR16) },
        { "24cs32",     AT24_DEVICE_MAGIC(16,
                                AT24_FLAG_ADDR16 |
                                AT24_FLAG_SERIAL |
                                AT24_FLAG_READONLY) },
        { "24c64",      AT24_DEVICE_MAGIC(65536 / 8,    AT24_FLAG_ADDR16) },
        { "24cs64",     AT24_DEVICE_MAGIC(16,
                                AT24_FLAG_ADDR16 |
                                AT24_FLAG_SERIAL |
                                AT24_FLAG_READONLY) },
        { "24c128",     AT24_DEVICE_MAGIC(131072 / 8,   AT24_FLAG_ADDR16) },
        { "24c256",     AT24_DEVICE_MAGIC(262144 / 8,   AT24_FLAG_ADDR16) },
        { "24c512",     AT24_DEVICE_MAGIC(524288 / 8,   AT24_FLAG_ADDR16) },
        { "24c1024",    AT24_DEVICE_MAGIC(1048576 / 8,  AT24_FLAG_ADDR16) },
        { "at24", 0 },
        { /* END OF LIST */ }
};
MODULE_DEVICE_TABLE(i2c, at24_ids);

static const struct acpi_device_id at24_acpi_ids[] = {
        { "INT3499", AT24_DEVICE_MAGIC(8192 / 8, 0) },
        { }
};
MODULE_DEVICE_TABLE(acpi, at24_acpi_ids);

/*-------------------------------------------------------------------------*/

/*
 * This routine supports chips which consume multiple I2C addresses. It
 * computes the addressing information to be used for a given r/w request.
 * Assumes that sanity checks for offset happened at sysfs-layer.
 *
 * Slave address and byte offset derive from the offset. Always
 * set the byte address; on a multi-master board, another master
 * may have changed the chip's "current" address pointer.
 *
 * REVISIT some multi-address chips don't rollover page reads to
 * the next slave address, so we may need to truncate the count.
 * Those chips might need another quirk flag.
 *
 * If the real hardware used four adjacent 24c02 chips and that
 * were misconfigured as one 24c08, that would be a similar effect:
 * one "eeprom" file not four, but larger reads would fail when
 * they crossed certain pages.
 */
static struct i2c_client *at24_translate_offset(struct at24_data *at24,
                                                unsigned int *offset)
{
        unsigned i;

        if (at24->chip.flags & AT24_FLAG_ADDR16) {
                i = *offset >> 16;
                *offset &= 0xffff;
        } else {
                i = *offset >> 8;
                *offset &= 0xff;
        }

        return at24->client[i];
}

static ssize_t at24_eeprom_read_smbus(struct at24_data *at24, char *buf,
                                      unsigned int offset, size_t count)
{
        unsigned long timeout, read_time;
        struct i2c_client *client;
        int status;

        client = at24_translate_offset(at24, &offset);

        if (count > io_limit)
                count = io_limit;

        /* Smaller eeproms can work given some SMBus extension calls */
        if (count > I2C_SMBUS_BLOCK_MAX)
                count = I2C_SMBUS_BLOCK_MAX;

        loop_until_timeout(timeout, read_time) {
                status = i2c_smbus_read_i2c_block_data_or_emulated(client,
                                                                   offset,
                                                                   count, buf);

                dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n",
                                count, offset, status, jiffies);

                if (status == count)
                        return count;
        }

        return -ETIMEDOUT;
}

static ssize_t at24_eeprom_read_i2c(struct at24_data *at24, char *buf,
                                    unsigned int offset, size_t count)
{
        unsigned long timeout, read_time;
        struct i2c_client *client;
        struct i2c_msg msg[2];
        int status, i;
        u8 msgbuf[2];

        memset(msg, 0, sizeof(msg));
        client = at24_translate_offset(at24, &offset);

        if (count > io_limit)
                count = io_limit;

        /*
         * When we have a better choice than SMBus calls, use a combined I2C
         * message. Write address; then read up to io_limit data bytes. Note
         * that read page rollover helps us here (unlike writes). msgbuf is
         * u8 and will cast to our needs.
         */
        i = 0;
        if (at24->chip.flags & AT24_FLAG_ADDR16)
                msgbuf[i++] = offset >> 8;
        msgbuf[i++] = offset;

        msg[0].addr = client->addr;
        msg[0].buf = msgbuf;
        msg[0].len = i;

        msg[1].addr = client->addr;
        msg[1].flags = I2C_M_RD;
        msg[1].buf = buf;
        msg[1].len = count;

        loop_until_timeout(timeout, read_time) {
                status = i2c_transfer(client->adapter, msg, 2);
                if (status == 2)
                        status = count;

                dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n",
                                count, offset, status, jiffies);

                if (status == count)
                        return count;
        }

        return -ETIMEDOUT;
}

static ssize_t at24_eeprom_read_serial(struct at24_data *at24, char *buf,
                                       unsigned int offset, size_t count)
{
        unsigned long timeout, read_time;
        struct i2c_client *client;
        struct i2c_msg msg[2];
        u8 addrbuf[2];
        int status;

        client = at24_translate_offset(at24, &offset);

        memset(msg, 0, sizeof(msg));
        msg[0].addr = client->addr;
        msg[0].buf = addrbuf;

        /*
         * The address pointer of the device is shared between the regular
         * EEPROM array and the serial number block. The dummy write (part of
         * the sequential read protocol) ensures the address pointer is reset
         * to the desired position.
         */
        if (at24->chip.flags & AT24_FLAG_ADDR16) {
                /*
                 * For 16 bit address pointers, the word address must contain
                 * a '10' sequence in bits 11 and 10 regardless of the
                 * intended position of the address pointer.
                 */
                addrbuf[0] = 0x08;
                addrbuf[1] = offset;
                msg[0].len = 2;
        } else {
                /*
                 * Otherwise the word address must begin with a '10' sequence,
                 * regardless of the intended address.
                 */
                addrbuf[0] = 0x80 + offset;
                msg[0].len = 1;
        }

        msg[1].addr = client->addr;
        msg[1].flags = I2C_M_RD;
        msg[1].buf = buf;
        msg[1].len = count;

        loop_until_timeout(timeout, read_time) {
                status = i2c_transfer(client->adapter, msg, 2);
                if (status == 2)
                        return count;
        }

        return -ETIMEDOUT;
}

static ssize_t at24_eeprom_read_mac(struct at24_data *at24, char *buf,
                                    unsigned int offset, size_t count)
{
        unsigned long timeout, read_time;
        struct i2c_client *client;
        struct i2c_msg msg[2];
        u8 addrbuf[2];
        int status;

        client = at24_translate_offset(at24, &offset);

        memset(msg, 0, sizeof(msg));
        msg[0].addr = client->addr;
        msg[0].buf = addrbuf;
        addrbuf[0] = 0x90 + offset;
        msg[0].len = 1;
        msg[1].addr = client->addr;
        msg[1].flags = I2C_M_RD;
        msg[1].buf = buf;
        msg[1].len = count;

        loop_until_timeout(timeout, read_time) {
                status = i2c_transfer(client->adapter, msg, 2);
                if (status == 2)
                        return count;
        }

        return -ETIMEDOUT;
}

/*
 * Note that if the hardware write-protect pin is pulled high, the whole
 * chip is normally write protected. But there are plenty of product
 * variants here, including OTP fuses and partial chip protect.
 *
 * We only use page mode writes; the alternative is sloooow. These routines
 * write at most one page.
 */

static size_t at24_adjust_write_count(struct at24_data *at24,
                                      unsigned int offset, size_t count)
{
        unsigned next_page;

        /* write_max is at most a page */
        if (count > at24->write_max)
                count = at24->write_max;

        /* Never roll over backwards, to the start of this page */
        next_page = roundup(offset + 1, at24->chip.page_size);
        if (offset + count > next_page)
                count = next_page - offset;

        return count;
}

static ssize_t at24_eeprom_write_smbus_block(struct at24_data *at24,
                                             const char *buf,
                                             unsigned int offset, size_t count)
{
        unsigned long timeout, write_time;
        struct i2c_client *client;
        ssize_t status = 0;

        client = at24_translate_offset(at24, &offset);
        count = at24_adjust_write_count(at24, offset, count);

        loop_until_timeout(timeout, write_time) {
                status = i2c_smbus_write_i2c_block_data(client,
                                                        offset, count, buf);
                if (status == 0)
                        status = count;

                dev_dbg(&client->dev, "write %zu@%d --> %zd (%ld)\n",
                                count, offset, status, jiffies);

                if (status == count)
                        return count;
        }

        return -ETIMEDOUT;
}

static ssize_t at24_eeprom_write_smbus_byte(struct at24_data *at24,
                                            const char *buf,
                                            unsigned int offset, size_t count)
{
        unsigned long timeout, write_time;
        struct i2c_client *client;
        ssize_t status = 0;

        client = at24_translate_offset(at24, &offset);

        loop_until_timeout(timeout, write_time) {
                status = i2c_smbus_write_byte_data(client, offset, buf[0]);
                if (status == 0)
                        status = count;

                dev_dbg(&client->dev, "write %zu@%d --> %zd (%ld)\n",
                                count, offset, status, jiffies);

                if (status == count)
                        return count;
        }

        return -ETIMEDOUT;
}

static ssize_t at24_eeprom_write_i2c(struct at24_data *at24, const char *buf,
                                     unsigned int offset, size_t count)
{
        unsigned long timeout, write_time;
        struct i2c_client *client;
        struct i2c_msg msg;
        ssize_t status = 0;
        int i = 0;

        client = at24_translate_offset(at24, &offset);
        count = at24_adjust_write_count(at24, offset, count);

        msg.addr = client->addr;
        msg.flags = 0;

        /* msg.buf is u8 and casts will mask the values */
        msg.buf = at24->writebuf;
        if (at24->chip.flags & AT24_FLAG_ADDR16)
                msg.buf[i++] = offset >> 8;

        msg.buf[i++] = offset;
        memcpy(&msg.buf[i], buf, count);
        msg.len = i + count;

        loop_until_timeout(timeout, write_time) {
                status = i2c_transfer(client->adapter, &msg, 1);
                if (status == 1)
                        status = count;

                dev_dbg(&client->dev, "write %zu@%d --> %zd (%ld)\n",
                                count, offset, status, jiffies);

                if (status == count)
                        return count;
        }

        return -ETIMEDOUT;
}

static int at24_read(void *priv, unsigned int off, void *val, size_t count)
{
        struct at24_data *at24 = priv;
        char *buf = val;

        if (unlikely(!count))
                return count;

        /*
         * Read data from chip, protecting against concurrent updates
         * from this host, but not from other I2C masters.
         */
        mutex_lock(&at24->lock);

        while (count) {
                int     status;

                status = at24->read_func(at24, buf, off, count);
                if (status < 0) {
                        mutex_unlock(&at24->lock);
                        return status;
                }
                buf += status;
                off += status;
                count -= status;
        }

        mutex_unlock(&at24->lock);

        return 0;
}

static int at24_write(void *priv, unsigned int off, void *val, size_t count)
{
        struct at24_data *at24 = priv;
        char *buf = val;

        if (unlikely(!count))
                return -EINVAL;

        /*
         * Write data to chip, protecting against concurrent updates
         * from this host, but not from other I2C masters.
         */
        mutex_lock(&at24->lock);

        while (count) {
                int status;

                status = at24->write_func(at24, buf, off, count);
                if (status < 0) {
                        mutex_unlock(&at24->lock);
                        return status;
                }
                buf += status;
                off += status;
                count -= status;
        }

        mutex_unlock(&at24->lock);

        return 0;
}

#ifdef CONFIG_OF
static void at24_get_ofdata(struct i2c_client *client,
                            struct at24_platform_data *chip)
{
        const __be32 *val;
        struct device_node *node = client->dev.of_node;

        if (node) {
                if (of_get_property(node, "read-only", NULL))
                        chip->flags |= AT24_FLAG_READONLY;
                val = of_get_property(node, "pagesize", NULL);
                if (val)
                        chip->page_size = be32_to_cpup(val);
        }
}
#else
static void at24_get_ofdata(struct i2c_client *client,
                            struct at24_platform_data *chip)
{ }
#endif /* CONFIG_OF */

static int at24_probe(struct i2c_client *client, const struct i2c_device_id *id)
{
        struct at24_platform_data chip;
        kernel_ulong_t magic = 0;
        bool writable;
        int use_smbus = 0;
        int use_smbus_write = 0;
        struct at24_data *at24;
        int err;
        unsigned i, num_addresses;
        u8 test_byte;

        if (client->dev.platform_data) {
                chip = *(struct at24_platform_data *)client->dev.platform_data;
        } else {
                if (id) {
                        magic = id->driver_data;
                } else {
                        const struct acpi_device_id *aid;

                        aid = acpi_match_device(at24_acpi_ids, &client->dev);
                        if (aid)
                                magic = aid->driver_data;
                }
                if (!magic)
                        return -ENODEV;

                chip.byte_len = BIT(magic & AT24_BITMASK(AT24_SIZE_BYTELEN));
                magic >>= AT24_SIZE_BYTELEN;
                chip.flags = magic & AT24_BITMASK(AT24_SIZE_FLAGS);
                /*
                 * This is slow, but we can't know all eeproms, so we better
                 * play safe. Specifying custom eeprom-types via platform_data
                 * is recommended anyhow.
                 */
                chip.page_size = 1;

                /* update chipdata if OF is present */
                at24_get_ofdata(client, &chip);

                chip.setup = NULL;
                chip.context = NULL;
        }

        if (!is_power_of_2(chip.byte_len))
                dev_warn(&client->dev,
                        "byte_len looks suspicious (no power of 2)!\n");
        if (!chip.page_size) {
                dev_err(&client->dev, "page_size must not be 0!\n");
                return -EINVAL;
        }
        if (!is_power_of_2(chip.page_size))
                dev_warn(&client->dev,
                        "page_size looks suspicious (no power of 2)!\n");

        /* Use I2C operations unless we're stuck with SMBus extensions. */
        if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
                if (chip.flags & AT24_FLAG_ADDR16)
                        return -EPFNOSUPPORT;

                if (i2c_check_functionality(client->adapter,
                                I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
                        use_smbus = I2C_SMBUS_I2C_BLOCK_DATA;
                } else if (i2c_check_functionality(client->adapter,
                                I2C_FUNC_SMBUS_READ_WORD_DATA)) {
                        use_smbus = I2C_SMBUS_WORD_DATA;
                } else if (i2c_check_functionality(client->adapter,
                                I2C_FUNC_SMBUS_READ_BYTE_DATA)) {
                        use_smbus = I2C_SMBUS_BYTE_DATA;
                } else {
                        return -EPFNOSUPPORT;
                }

                if (i2c_check_functionality(client->adapter,
                                I2C_FUNC_SMBUS_WRITE_I2C_BLOCK)) {
                        use_smbus_write = I2C_SMBUS_I2C_BLOCK_DATA;
                } else if (i2c_check_functionality(client->adapter,
                                I2C_FUNC_SMBUS_WRITE_BYTE_DATA)) {
                        use_smbus_write = I2C_SMBUS_BYTE_DATA;
                        chip.page_size = 1;
                }
        }

        if (chip.flags & AT24_FLAG_TAKE8ADDR)
                num_addresses = 8;
        else
                num_addresses = DIV_ROUND_UP(chip.byte_len,
                        (chip.flags & AT24_FLAG_ADDR16) ? 65536 : 256);

        at24 = devm_kzalloc(&client->dev, sizeof(struct at24_data) +
                num_addresses * sizeof(struct i2c_client *), GFP_KERNEL);
        if (!at24)
                return -ENOMEM;

        mutex_init(&at24->lock);
        at24->use_smbus = use_smbus;
        at24->use_smbus_write = use_smbus_write;
        at24->chip = chip;
        at24->num_addresses = num_addresses;

        if ((chip.flags & AT24_FLAG_SERIAL) && (chip.flags & AT24_FLAG_MAC)) {
                dev_err(&client->dev,
                        "invalid device data - cannot have both AT24_FLAG_SERIAL & AT24_FLAG_MAC.");
                return -EINVAL;
        }

        if (chip.flags & AT24_FLAG_SERIAL) {
                at24->read_func = at24_eeprom_read_serial;
        } else if (chip.flags & AT24_FLAG_MAC) {
                at24->read_func = at24_eeprom_read_mac;
        } else {
                at24->read_func = at24->use_smbus ? at24_eeprom_read_smbus
                                                  : at24_eeprom_read_i2c;
        }

        if (at24->use_smbus) {
                if (at24->use_smbus_write == I2C_SMBUS_I2C_BLOCK_DATA)
                        at24->write_func = at24_eeprom_write_smbus_block;
                else
                        at24->write_func = at24_eeprom_write_smbus_byte;
        } else {
                at24->write_func = at24_eeprom_write_i2c;
        }

        writable = !(chip.flags & AT24_FLAG_READONLY);
        if (writable) {
                if (!use_smbus || use_smbus_write) {

                        unsigned write_max = chip.page_size;

                        if (write_max > io_limit)
                                write_max = io_limit;
                        if (use_smbus && write_max > I2C_SMBUS_BLOCK_MAX)
                                write_max = I2C_SMBUS_BLOCK_MAX;
                        at24->write_max = write_max;

                        /* buffer (data + address at the beginning) */
                        at24->writebuf = devm_kzalloc(&client->dev,
                                write_max + 2, GFP_KERNEL);
                        if (!at24->writebuf)
                                return -ENOMEM;
                } else {
                        dev_warn(&client->dev,
                                "cannot write due to controller restrictions.");
                }
        }

        at24->client[0] = client;

        /* use dummy devices for multiple-address chips */
        for (i = 1; i < num_addresses; i++) {
                at24->client[i] = i2c_new_dummy(client->adapter,
                                        client->addr + i);
                if (!at24->client[i]) {
                        dev_err(&client->dev, "address 0x%02x unavailable\n",
                                        client->addr + i);
                        err = -EADDRINUSE;
                        goto err_clients;
                }
        }

        i2c_set_clientdata(client, at24);

        /*
         * Perform a one-byte test read to verify that the
         * chip is functional.
         */
        err = at24_read(at24, 0, &test_byte, 1);
        if (err) {
                err = -ENODEV;
                goto err_clients;
        }

        at24->nvmem_config.name = dev_name(&client->dev);
        at24->nvmem_config.dev = &client->dev;
        at24->nvmem_config.read_only = !writable;
        at24->nvmem_config.root_only = true;
        at24->nvmem_config.owner = THIS_MODULE;
        at24->nvmem_config.compat = true;
        at24->nvmem_config.base_dev = &client->dev;
        at24->nvmem_config.reg_read = at24_read;
        at24->nvmem_config.reg_write = at24_write;
        at24->nvmem_config.priv = at24;
        at24->nvmem_config.stride = 4;
        at24->nvmem_config.word_size = 1;
        at24->nvmem_config.size = chip.byte_len;

        at24->nvmem = nvmem_register(&at24->nvmem_config);

        if (IS_ERR(at24->nvmem)) {
                err = PTR_ERR(at24->nvmem);
                goto err_clients;
        }

        dev_info(&client->dev, "%u byte %s EEPROM, %s, %u bytes/write\n",
                chip.byte_len, client->name,
                writable ? "writable" : "read-only", at24->write_max);
        if (use_smbus == I2C_SMBUS_WORD_DATA ||
            use_smbus == I2C_SMBUS_BYTE_DATA) {
                dev_notice(&client->dev, "Falling back to %s reads, "
                           "performance will suffer\n", use_smbus ==
                           I2C_SMBUS_WORD_DATA ? "word" : "byte");
        }

        /* export data to kernel code */
        if (chip.setup)
                chip.setup(at24->nvmem, chip.context);

        return 0;

err_clients:
        for (i = 1; i < num_addresses; i++)
                if (at24->client[i])
                        i2c_unregister_device(at24->client[i]);

        return err;
}

static int at24_remove(struct i2c_client *client)
{
        struct at24_data *at24;
        int i;

        at24 = i2c_get_clientdata(client);

        nvmem_unregister(at24->nvmem);

        for (i = 1; i < at24->num_addresses; i++)
                i2c_unregister_device(at24->client[i]);

        return 0;
}

/*-------------------------------------------------------------------------*/

static struct i2c_driver at24_driver = {
        .driver = {
                .name = "at24",
                .acpi_match_table = ACPI_PTR(at24_acpi_ids),
        },
        .probe = at24_probe,
        .remove = at24_remove,
        .id_table = at24_ids,
};

static int __init at24_init(void)
{
        if (!io_limit) {
                pr_err("at24: io_limit must not be 0!\n");
                return -EINVAL;
        }

        io_limit = rounddown_pow_of_two(io_limit);
        return i2c_add_driver(&at24_driver);
}
module_init(at24_init);

static void __exit at24_exit(void)
{
        i2c_del_driver(&at24_driver);
}
module_exit(at24_exit);

MODULE_DESCRIPTION("Driver for most I2C EEPROMs");
MODULE_AUTHOR("David Brownell and Wolfram Sang");
MODULE_LICENSE("GPL");