// SPDX-License-Identifier: GPL-2.0-only
/*
 * max6875.c - driver for MAX6874/MAX6875
 *
 * Copyright (C) 2005 Ben Gardner <bgardner@wabtec.com>
 *
 * Based on eeprom.c
 *
 * The MAX6875 has a bank of registers and two banks of EEPROM.
 * Address ranges are defined as follows:
 *  * 0x0000 - 0x0046 = configuration registers
 *  * 0x8000 - 0x8046 = configuration EEPROM
 *  * 0x8100 - 0x82FF = user EEPROM
 *
 * This driver makes the user EEPROM available for read.
 *
 * The registers & config EEPROM should be accessed via i2c-dev.
 *
 * The MAX6875 ignores the lowest address bit, so each chip responds to
 * two addresses - 0x50/0x51 and 0x52/0x53.
 *
 * Note that the MAX6875 uses i2c_smbus_write_byte_data() to set the read
 * address, so this driver is destructive if loaded for the wrong EEPROM chip.
 */

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

/* The MAX6875 can only read/write 16 bytes at a time */
#define SLICE_SIZE                      16
#define SLICE_BITS                      4

/* USER EEPROM is at addresses 0x8100 - 0x82FF */
#define USER_EEPROM_BASE                0x8100
#define USER_EEPROM_SIZE                0x0200
#define USER_EEPROM_SLICES              32

/* MAX6875 commands */
#define MAX6875_CMD_BLK_READ            0x84

/* Each client has this additional data */
struct max6875_data {
        struct i2c_client       *fake_client;
        struct mutex            update_lock;

        u32                     valid;
        u8                      data[USER_EEPROM_SIZE];
        unsigned long           last_updated[USER_EEPROM_SLICES];
};

static void max6875_update_slice(struct i2c_client *client, int slice)
{
        struct max6875_data *data = i2c_get_clientdata(client);
        int i, j, addr;
        u8 *buf;

        if (slice >= USER_EEPROM_SLICES)
                return;

        mutex_lock(&data->update_lock);

        buf = &data->data[slice << SLICE_BITS];

        if (!(data->valid & (1 << slice)) ||
            time_after(jiffies, data->last_updated[slice])) {

                dev_dbg(&client->dev, "Starting update of slice %u\n", slice);

                data->valid &= ~(1 << slice);

                addr = USER_EEPROM_BASE + (slice << SLICE_BITS);

                /* select the eeprom address */
                if (i2c_smbus_write_byte_data(client, addr >> 8, addr & 0xFF)) {
                        dev_err(&client->dev, "address set failed\n");
                        goto exit_up;
                }

                if (i2c_check_functionality(client->adapter,
                                            I2C_FUNC_SMBUS_READ_I2C_BLOCK)) {
                        if (i2c_smbus_read_i2c_block_data(client,
                                                          MAX6875_CMD_BLK_READ,
                                                          SLICE_SIZE,
                                                          buf) != SLICE_SIZE) {
                                goto exit_up;
                        }
                } else {
                        for (i = 0; i < SLICE_SIZE; i++) {
                                j = i2c_smbus_read_byte(client);
                                if (j < 0) {
                                        goto exit_up;
                                }
                                buf[i] = j;
                        }
                }
                data->last_updated[slice] = jiffies;
                data->valid |= (1 << slice);
        }
exit_up:
        mutex_unlock(&data->update_lock);
}

static ssize_t max6875_read(struct file *filp, struct kobject *kobj,
                            const struct bin_attribute *bin_attr,
                            char *buf, loff_t off, size_t count)
{
        struct i2c_client *client = kobj_to_i2c_client(kobj);
        struct max6875_data *data = i2c_get_clientdata(client);
        int slice, max_slice;

        /* refresh slices which contain requested bytes */
        max_slice = (off + count - 1) >> SLICE_BITS;
        for (slice = (off >> SLICE_BITS); slice <= max_slice; slice++)
                max6875_update_slice(client, slice);

        memcpy(buf, &data->data[off], count);

        return count;
}

static const struct bin_attribute user_eeprom_attr = {
        .attr = {
                .name = "eeprom",
                .mode = S_IRUGO,
        },
        .size = USER_EEPROM_SIZE,
        .read = max6875_read,
};

static int max6875_probe(struct i2c_client *client)
{
        struct i2c_adapter *adapter = client->adapter;
        struct max6875_data *data;
        int err;

        if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_BYTE_DATA
                                     | I2C_FUNC_SMBUS_READ_BYTE))
                return -ENODEV;

        /* Only bind to even addresses */
        if (client->addr & 1)
                return -ENODEV;

        data = kzalloc_obj(struct max6875_data);
        if (!data)
                return -ENOMEM;

        /* A fake client is created on the odd address */
        data->fake_client = i2c_new_dummy_device(client->adapter, client->addr + 1);
        if (IS_ERR(data->fake_client)) {
                err = PTR_ERR(data->fake_client);
                goto exit_kfree;
        }

        /* Init real i2c_client */
        i2c_set_clientdata(client, data);
        mutex_init(&data->update_lock);

        err = sysfs_create_bin_file(&client->dev.kobj, &user_eeprom_attr);
        if (err)
                goto exit_remove_fake;

        return 0;

exit_remove_fake:
        i2c_unregister_device(data->fake_client);
exit_kfree:
        kfree(data);
        return err;
}

static void max6875_remove(struct i2c_client *client)
{
        struct max6875_data *data = i2c_get_clientdata(client);

        i2c_unregister_device(data->fake_client);

        sysfs_remove_bin_file(&client->dev.kobj, &user_eeprom_attr);
        kfree(data);
}

static const struct i2c_device_id max6875_id[] = {
        { "max6875" },
        { }
};
MODULE_DEVICE_TABLE(i2c, max6875_id);

static struct i2c_driver max6875_driver = {
        .driver = {
                .name   = "max6875",
        },
        .probe          = max6875_probe,
        .remove         = max6875_remove,
        .id_table       = max6875_id,
};

module_i2c_driver(max6875_driver);

MODULE_AUTHOR("Ben Gardner <bgardner@wabtec.com>");
MODULE_DESCRIPTION("MAX6875 driver");
MODULE_LICENSE("GPL");