max6875.c

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/*
 * max6875.c - driver for MAX6874/MAX6875
 *
 * Copyright (C) 2005 Ben Gardner <[email protected]>
 *
 * 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.
 *
 * 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; version 2 of the License.
 */

#include <linux/kernel.h>
#include <linux/init.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,
                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;

    if (off > USER_EEPROM_SIZE)
        return 0;

    if (off + count > USER_EEPROM_SIZE)
        count = USER_EEPROM_SIZE - off;

    /* 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 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,
             const struct i2c_device_id *id)
{
    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;

    if (!(data = kzalloc(sizeof(struct max6875_data), GFP_KERNEL)))
        return -ENOMEM;

    /* A fake client is created on the odd address */
    data->fake_client = i2c_new_dummy(client->adapter, client->addr + 1);
    if (!data->fake_client) {
        err = -ENOMEM;
        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 int 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);

    return 0;
}

static const struct i2c_device_id max6875_id[] = {
    { "max6875", 0 },
    { }
};

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 <[email protected]>");
MODULE_DESCRIPTION("MAX6875 driver");
MODULE_LICENSE("GPL");