// SPDX-License-Identifier: GPL-2.0+
/*
 * at24.c - handle most I2C EEPROMs
 *
 * Copyright (C) 2005-2007 David Brownell
 * Copyright (C) 2008 Wolfram Sang, Pengutronix
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/of_device.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/property.h>
#include <linux/acpi.h>
#include <linux/i2c.h>
#include <linux/nvmem-provider.h>
#include <linux/regmap.h>
#include <linux/platform_data/at24.h>
#include <linux/pm_runtime.h>
#include <linux/gpio/consumer.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_client {
        struct i2c_client *client;
        struct regmap *regmap;
};

struct at24_data {
        /*
         * Lock protects against activities from other Linux tasks,
         * but not from changes by other I2C masters.
         */
        struct mutex lock;

        unsigned int write_max;
        unsigned int num_addresses;
        unsigned int offset_adj;

        u32 byte_len;
        u16 page_size;
        u8 flags;

        struct nvmem_device *nvmem;

        struct gpio_desc *wp_gpio;

        /*
         * Some chips tie up multiple I2C addresses; dummy devices reserve
         * them for us, and we'll use them with SMBus calls.
         */
        struct at24_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 int at24_io_limit = 128;
module_param_named(io_limit, at24_io_limit, uint, 0);
MODULE_PARM_DESC(at24_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 int at24_write_timeout = 25;
module_param_named(write_timeout, at24_write_timeout, uint, 0);
MODULE_PARM_DESC(at24_write_timeout, "Time (in ms) to try writes (default 25)");

/*
 * 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 at24_loop_until_timeout(tout, op_time)                          \
        for (tout = jiffies + msecs_to_jiffies(at24_write_timeout),     \
             op_time = 0;                                               \
             op_time ? time_before(op_time, tout) : true;               \
             usleep_range(1000, 1500), op_time = jiffies)

struct at24_chip_data {
        /*
         * these fields mirror their equivalents in
         * struct at24_platform_data
         */
        u32 byte_len;
        u8 flags;
};

#define AT24_CHIP_DATA(_name, _len, _flags)                             \
        static const struct at24_chip_data _name = {                    \
                .byte_len = _len, .flags = _flags,                      \
        }

/* needs 8 addresses as A0-A2 are ignored */
AT24_CHIP_DATA(at24_data_24c00, 128 / 8, AT24_FLAG_TAKE8ADDR);
/* old variants can't be handled with this generic entry! */
AT24_CHIP_DATA(at24_data_24c01, 1024 / 8, 0);
AT24_CHIP_DATA(at24_data_24cs01, 16,
        AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
AT24_CHIP_DATA(at24_data_24c02, 2048 / 8, 0);
AT24_CHIP_DATA(at24_data_24cs02, 16,
        AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
AT24_CHIP_DATA(at24_data_24mac402, 48 / 8,
        AT24_FLAG_MAC | AT24_FLAG_READONLY);
AT24_CHIP_DATA(at24_data_24mac602, 64 / 8,
        AT24_FLAG_MAC | AT24_FLAG_READONLY);
/* spd is a 24c02 in memory DIMMs */
AT24_CHIP_DATA(at24_data_spd, 2048 / 8,
        AT24_FLAG_READONLY | AT24_FLAG_IRUGO);
AT24_CHIP_DATA(at24_data_24c04, 4096 / 8, 0);
AT24_CHIP_DATA(at24_data_24cs04, 16,
        AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
/* 24rf08 quirk is handled at i2c-core */
AT24_CHIP_DATA(at24_data_24c08, 8192 / 8, 0);
AT24_CHIP_DATA(at24_data_24cs08, 16,
        AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
AT24_CHIP_DATA(at24_data_24c16, 16384 / 8, 0);
AT24_CHIP_DATA(at24_data_24cs16, 16,
        AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
AT24_CHIP_DATA(at24_data_24c32, 32768 / 8, AT24_FLAG_ADDR16);
AT24_CHIP_DATA(at24_data_24cs32, 16,
        AT24_FLAG_ADDR16 | AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
AT24_CHIP_DATA(at24_data_24c64, 65536 / 8, AT24_FLAG_ADDR16);
AT24_CHIP_DATA(at24_data_24cs64, 16,
        AT24_FLAG_ADDR16 | AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
AT24_CHIP_DATA(at24_data_24c128, 131072 / 8, AT24_FLAG_ADDR16);
AT24_CHIP_DATA(at24_data_24c256, 262144 / 8, AT24_FLAG_ADDR16);
AT24_CHIP_DATA(at24_data_24c512, 524288 / 8, AT24_FLAG_ADDR16);
AT24_CHIP_DATA(at24_data_24c1024, 1048576 / 8, AT24_FLAG_ADDR16);
/* identical to 24c08 ? */
AT24_CHIP_DATA(at24_data_INT3499, 8192 / 8, 0);

static const struct i2c_device_id at24_ids[] = {
        { "24c00",      (kernel_ulong_t)&at24_data_24c00 },
        { "24c01",      (kernel_ulong_t)&at24_data_24c01 },
        { "24cs01",     (kernel_ulong_t)&at24_data_24cs01 },
        { "24c02",      (kernel_ulong_t)&at24_data_24c02 },
        { "24cs02",     (kernel_ulong_t)&at24_data_24cs02 },
        { "24mac402",   (kernel_ulong_t)&at24_data_24mac402 },
        { "24mac602",   (kernel_ulong_t)&at24_data_24mac602 },
        { "spd",        (kernel_ulong_t)&at24_data_spd },
        { "24c04",      (kernel_ulong_t)&at24_data_24c04 },
        { "24cs04",     (kernel_ulong_t)&at24_data_24cs04 },
        { "24c08",      (kernel_ulong_t)&at24_data_24c08 },
        { "24cs08",     (kernel_ulong_t)&at24_data_24cs08 },
        { "24c16",      (kernel_ulong_t)&at24_data_24c16 },
        { "24cs16",     (kernel_ulong_t)&at24_data_24cs16 },
        { "24c32",      (kernel_ulong_t)&at24_data_24c32 },
        { "24cs32",     (kernel_ulong_t)&at24_data_24cs32 },
        { "24c64",      (kernel_ulong_t)&at24_data_24c64 },
        { "24cs64",     (kernel_ulong_t)&at24_data_24cs64 },
        { "24c128",     (kernel_ulong_t)&at24_data_24c128 },
        { "24c256",     (kernel_ulong_t)&at24_data_24c256 },
        { "24c512",     (kernel_ulong_t)&at24_data_24c512 },
        { "24c1024",    (kernel_ulong_t)&at24_data_24c1024 },
        { "at24",       0 },
        { /* END OF LIST */ }
};
MODULE_DEVICE_TABLE(i2c, at24_ids);

static const struct of_device_id at24_of_match[] = {
        { .compatible = "atmel,24c00",          .data = &at24_data_24c00 },
        { .compatible = "atmel,24c01",          .data = &at24_data_24c01 },
        { .compatible = "atmel,24cs01",         .data = &at24_data_24cs01 },
        { .compatible = "atmel,24c02",          .data = &at24_data_24c02 },
        { .compatible = "atmel,24cs02",         .data = &at24_data_24cs02 },
        { .compatible = "atmel,24mac402",       .data = &at24_data_24mac402 },
        { .compatible = "atmel,24mac602",       .data = &at24_data_24mac602 },
        { .compatible = "atmel,spd",            .data = &at24_data_spd },
        { .compatible = "atmel,24c04",          .data = &at24_data_24c04 },
        { .compatible = "atmel,24cs04",         .data = &at24_data_24cs04 },
        { .compatible = "atmel,24c08",          .data = &at24_data_24c08 },
        { .compatible = "atmel,24cs08",         .data = &at24_data_24cs08 },
        { .compatible = "atmel,24c16",          .data = &at24_data_24c16 },
        { .compatible = "atmel,24cs16",         .data = &at24_data_24cs16 },
        { .compatible = "atmel,24c32",          .data = &at24_data_24c32 },
        { .compatible = "atmel,24cs32",         .data = &at24_data_24cs32 },
        { .compatible = "atmel,24c64",          .data = &at24_data_24c64 },
        { .compatible = "atmel,24cs64",         .data = &at24_data_24cs64 },
        { .compatible = "atmel,24c128",         .data = &at24_data_24c128 },
        { .compatible = "atmel,24c256",         .data = &at24_data_24c256 },
        { .compatible = "atmel,24c512",         .data = &at24_data_24c512 },
        { .compatible = "atmel,24c1024",        .data = &at24_data_24c1024 },
        { /* END OF LIST */ },
};
MODULE_DEVICE_TABLE(of, at24_of_match);

static const struct acpi_device_id at24_acpi_ids[] = {
        { "INT3499",    (kernel_ulong_t)&at24_data_INT3499 },
        { /* END OF LIST */ }
};
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.
 */
static struct at24_client *at24_translate_offset(struct at24_data *at24,
                                                 unsigned int *offset)
{
        unsigned int i;

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

        return &at24->client[i];
}

static struct device *at24_base_client_dev(struct at24_data *at24)
{
        return &at24->client[0].client->dev;
}

static size_t at24_adjust_read_count(struct at24_data *at24,
                                      unsigned int offset, size_t count)
{
        unsigned int bits;
        size_t remainder;

        /*
         * In case of multi-address chips that don't rollover reads to
         * the next slave address: truncate the count to the slave boundary,
         * so that the read never straddles slaves.
         */
        if (at24->flags & AT24_FLAG_NO_RDROL) {
                bits = (at24->flags & AT24_FLAG_ADDR16) ? 16 : 8;
                remainder = BIT(bits) - offset;
                if (count > remainder)
                        count = remainder;
        }

        if (count > at24_io_limit)
                count = at24_io_limit;

        return count;
}

static ssize_t at24_regmap_read(struct at24_data *at24, char *buf,
                                unsigned int offset, size_t count)
{
        unsigned long timeout, read_time;
        struct at24_client *at24_client;
        struct i2c_client *client;
        struct regmap *regmap;
        int ret;

        at24_client = at24_translate_offset(at24, &offset);
        regmap = at24_client->regmap;
        client = at24_client->client;
        count = at24_adjust_read_count(at24, offset, count);

        /* adjust offset for mac and serial read ops */
        offset += at24->offset_adj;

        at24_loop_until_timeout(timeout, read_time) {
                ret = regmap_bulk_read(regmap, offset, buf, count);
                dev_dbg(&client->dev, "read %zu@%d --> %d (%ld)\n",
                        count, offset, ret, jiffies);
                if (!ret)
                        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 int 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->page_size);
        if (offset + count > next_page)
                count = next_page - offset;

        return count;
}

static ssize_t at24_regmap_write(struct at24_data *at24, const char *buf,
                                 unsigned int offset, size_t count)
{
        unsigned long timeout, write_time;
        struct at24_client *at24_client;
        struct i2c_client *client;
        struct regmap *regmap;
        int ret;

        at24_client = at24_translate_offset(at24, &offset);
        regmap = at24_client->regmap;
        client = at24_client->client;
        count = at24_adjust_write_count(at24, offset, count);

        at24_loop_until_timeout(timeout, write_time) {
                ret = regmap_bulk_write(regmap, offset, buf, count);
                dev_dbg(&client->dev, "write %zu@%d --> %d (%ld)\n",
                        count, offset, ret, jiffies);
                if (!ret)
                        return count;
        }

        return -ETIMEDOUT;
}

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

        at24 = priv;
        dev = at24_base_client_dev(at24);

        if (unlikely(!count))
                return count;

        if (off + count > at24->byte_len)
                return -EINVAL;

        ret = pm_runtime_get_sync(dev);
        if (ret < 0) {
                pm_runtime_put_noidle(dev);
                return ret;
        }

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

        while (count) {
                ret = at24_regmap_read(at24, buf, off, count);
                if (ret < 0) {
                        mutex_unlock(&at24->lock);
                        pm_runtime_put(dev);
                        return ret;
                }
                buf += ret;
                off += ret;
                count -= ret;
        }

        mutex_unlock(&at24->lock);

        pm_runtime_put(dev);

        return 0;
}

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

        at24 = priv;
        dev = at24_base_client_dev(at24);

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

        if (off + count > at24->byte_len)
                return -EINVAL;

        ret = pm_runtime_get_sync(dev);
        if (ret < 0) {
                pm_runtime_put_noidle(dev);
                return ret;
        }

        /*
         * Write data to chip, protecting against concurrent updates
         * from this host, but not from other I2C masters.
         */
        mutex_lock(&at24->lock);
        gpiod_set_value_cansleep(at24->wp_gpio, 0);

        while (count) {
                ret = at24_regmap_write(at24, buf, off, count);
                if (ret < 0) {
                        gpiod_set_value_cansleep(at24->wp_gpio, 1);
                        mutex_unlock(&at24->lock);
                        pm_runtime_put(dev);
                        return ret;
                }
                buf += ret;
                off += ret;
                count -= ret;
        }

        gpiod_set_value_cansleep(at24->wp_gpio, 1);
        mutex_unlock(&at24->lock);

        pm_runtime_put(dev);

        return 0;
}

static void at24_properties_to_pdata(struct device *dev,
                                     struct at24_platform_data *chip)
{
        int err;
        u32 val;

        if (device_property_present(dev, "read-only"))
                chip->flags |= AT24_FLAG_READONLY;
        if (device_property_present(dev, "no-read-rollover"))
                chip->flags |= AT24_FLAG_NO_RDROL;

        err = device_property_read_u32(dev, "size", &val);
        if (!err)
                chip->byte_len = val;

        err = device_property_read_u32(dev, "pagesize", &val);
        if (!err) {
                chip->page_size = val;
        } else {
                /*
                 * 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;
        }
}

static int at24_get_pdata(struct device *dev, struct at24_platform_data *pdata)
{
        struct device_node *of_node = dev->of_node;
        const struct at24_chip_data *cdata;
        const struct i2c_device_id *id;
        struct at24_platform_data *pd;

        pd = dev_get_platdata(dev);
        if (pd) {
                memcpy(pdata, pd, sizeof(*pdata));
                return 0;
        }

        id = i2c_match_id(at24_ids, to_i2c_client(dev));

        /*
         * The I2C core allows OF nodes compatibles to match against the
         * I2C device ID table as a fallback, so check not only if an OF
         * node is present but also if it matches an OF device ID entry.
         */
        if (of_node && of_match_device(at24_of_match, dev))
                cdata = of_device_get_match_data(dev);
        else if (id)
                cdata = (void *)id->driver_data;
        else
                cdata = acpi_device_get_match_data(dev);

        if (!cdata)
                return -ENODEV;

        pdata->byte_len = cdata->byte_len;
        pdata->flags = cdata->flags;
        at24_properties_to_pdata(dev, pdata);

        return 0;
}

static unsigned int at24_get_offset_adj(u8 flags, unsigned int byte_len)
{
        if (flags & AT24_FLAG_MAC) {
                /* EUI-48 starts from 0x9a, EUI-64 from 0x98 */
                return 0xa0 - byte_len;
        } else if (flags & AT24_FLAG_SERIAL && 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.
                 */
                return 0x0800;
        } else if (flags & AT24_FLAG_SERIAL) {
                /*
                 * Otherwise the word address must begin with a '10' sequence,
                 * regardless of the intended address.
                 */
                return 0x0080;
        } else {
                return 0;
        }
}

static int at24_probe(struct i2c_client *client)
{
        struct regmap_config regmap_config = { };
        struct nvmem_config nvmem_config = { };
        struct at24_platform_data pdata = { };
        struct device *dev = &client->dev;
        bool i2c_fn_i2c, i2c_fn_block;
        unsigned int i, num_addresses;
        struct at24_data *at24;
        struct regmap *regmap;
        size_t at24_size;
        bool writable;
        u8 test_byte;
        int err;

        i2c_fn_i2c = i2c_check_functionality(client->adapter, I2C_FUNC_I2C);
        i2c_fn_block = i2c_check_functionality(client->adapter,
                                               I2C_FUNC_SMBUS_WRITE_I2C_BLOCK);

        err = at24_get_pdata(dev, &pdata);
        if (err)
                return err;

        if (!i2c_fn_i2c && !i2c_fn_block)
                pdata.page_size = 1;

        if (!pdata.page_size) {
                dev_err(dev, "page_size must not be 0!\n");
                return -EINVAL;
        }

        if (!is_power_of_2(pdata.page_size))
                dev_warn(dev, "page_size looks suspicious (no power of 2)!\n");

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

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

        regmap_config.val_bits = 8;
        regmap_config.reg_bits = (pdata.flags & AT24_FLAG_ADDR16) ? 16 : 8;
        regmap_config.disable_locking = true;

        regmap = devm_regmap_init_i2c(client, &regmap_config);
        if (IS_ERR(regmap))
                return PTR_ERR(regmap);

        at24_size = sizeof(*at24) + num_addresses * sizeof(struct at24_client);
        at24 = devm_kzalloc(dev, at24_size, GFP_KERNEL);
        if (!at24)
                return -ENOMEM;

        mutex_init(&at24->lock);
        at24->byte_len = pdata.byte_len;
        at24->page_size = pdata.page_size;
        at24->flags = pdata.flags;
        at24->num_addresses = num_addresses;
        at24->offset_adj = at24_get_offset_adj(pdata.flags, pdata.byte_len);
        at24->client[0].client = client;
        at24->client[0].regmap = regmap;

        at24->wp_gpio = devm_gpiod_get_optional(dev, "wp", GPIOD_OUT_HIGH);
        if (IS_ERR(at24->wp_gpio))
                return PTR_ERR(at24->wp_gpio);

        writable = !(pdata.flags & AT24_FLAG_READONLY);
        if (writable) {
                at24->write_max = min_t(unsigned int,
                                        pdata.page_size, at24_io_limit);
                if (!i2c_fn_i2c && at24->write_max > I2C_SMBUS_BLOCK_MAX)
                        at24->write_max = I2C_SMBUS_BLOCK_MAX;
        }

        /* use dummy devices for multiple-address chips */
        for (i = 1; i < num_addresses; i++) {
                at24->client[i].client = i2c_new_dummy(client->adapter,
                                                       client->addr + i);
                if (!at24->client[i].client) {
                        dev_err(dev, "address 0x%02x unavailable\n",
                                client->addr + i);
                        err = -EADDRINUSE;
                        goto err_clients;
                }
                at24->client[i].regmap = devm_regmap_init_i2c(
                                                at24->client[i].client,
                                                &regmap_config);
                if (IS_ERR(at24->client[i].regmap)) {
                        err = PTR_ERR(at24->client[i].regmap);
                        goto err_clients;
                }
        }

        i2c_set_clientdata(client, at24);

        /* enable runtime pm */
        pm_runtime_set_active(dev);
        pm_runtime_enable(dev);

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

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

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

        dev_info(dev, "%u byte %s EEPROM, %s, %u bytes/write\n",
                 pdata.byte_len, client->name,
                 writable ? "writable" : "read-only", at24->write_max);

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

        return 0;

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

        pm_runtime_disable(dev);

        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].client);

        pm_runtime_disable(&client->dev);
        pm_runtime_set_suspended(&client->dev);

        return 0;
}

static struct i2c_driver at24_driver = {
        .driver = {
                .name = "at24",
                .of_match_table = at24_of_match,
                .acpi_match_table = ACPI_PTR(at24_acpi_ids),
        },
        .probe_new = at24_probe,
        .remove = at24_remove,
        .id_table = at24_ids,
};

static int __init at24_init(void)
{
        if (!at24_io_limit) {
                pr_err("at24: at24_io_limit must not be 0!\n");
                return -EINVAL;
        }

        at24_io_limit = rounddown_pow_of_two(at24_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");