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max6875.c

/*
    max6875.c - driver for MAX6874/MAX6875

    Copyright (C) 2005 Ben Gardner <bgardner@wabtec.com>

    Based on i2c/chips/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>

/* Do not scan - the MAX6875 access method will write to some EEPROM chips */
static unsigned short normal_i2c[] = {I2C_CLIENT_END};

/* Insmod parameters */
I2C_CLIENT_INSMOD_1(max6875);

/* 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 client;
      struct mutex            update_lock;

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

static int max6875_attach_adapter(struct i2c_adapter *adapter);
static int max6875_detect(struct i2c_adapter *adapter, int address, int kind);
static int max6875_detach_client(struct i2c_client *client);

/* This is the driver that will be inserted */
static struct i2c_driver max6875_driver = {
      .driver = {
            .name = "max6875",
      },
      .attach_adapter   = max6875_attach_adapter,
      .detach_client    = max6875_detach_client,
};

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 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_attach_adapter(struct i2c_adapter *adapter)
{
      return i2c_probe(adapter, &addr_data, max6875_detect);
}

/* This function is called by i2c_probe */
static int max6875_detect(struct i2c_adapter *adapter, int address, int kind)
{
      struct i2c_client *real_client;
      struct i2c_client *fake_client;
      struct max6875_data *data;
      int err = 0;

      if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_WRITE_BYTE_DATA
                             | I2C_FUNC_SMBUS_READ_BYTE))
            return 0;

      /* Only check even addresses */
      if (address & 1)
            return 0;

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

      /* A fake client is created on the odd address */
      if (!(fake_client = kzalloc(sizeof(struct i2c_client), GFP_KERNEL))) {
            err = -ENOMEM;
            goto exit_kfree1;
      }

      /* Init real i2c_client */
      real_client = &data->client;
      i2c_set_clientdata(real_client, data);
      real_client->addr = address;
      real_client->adapter = adapter;
      real_client->driver = &max6875_driver;
      real_client->flags = 0;
      strlcpy(real_client->name, "max6875", I2C_NAME_SIZE);
      mutex_init(&data->update_lock);

      /* Init fake client data */
      i2c_set_clientdata(fake_client, NULL);
      fake_client->addr = address | 1;
      fake_client->adapter = adapter;
      fake_client->driver = &max6875_driver;
      fake_client->flags = 0;
      strlcpy(fake_client->name, "max6875 subclient", I2C_NAME_SIZE);

      /* Prevent 24RF08 corruption (in case of user error) */
      i2c_smbus_write_quick(real_client, 0);

      if ((err = i2c_attach_client(real_client)) != 0)
            goto exit_kfree2;

      if ((err = i2c_attach_client(fake_client)) != 0)
            goto exit_detach1;

      err = sysfs_create_bin_file(&real_client->dev.kobj, &user_eeprom_attr);
      if (err)
            goto exit_detach2;

      return 0;

exit_detach2:
      i2c_detach_client(fake_client);
exit_detach1:
      i2c_detach_client(real_client);
exit_kfree2:
      kfree(fake_client);
exit_kfree1:
      kfree(data);
      return err;
}

/* Will be called for both the real client and the fake client */
static int max6875_detach_client(struct i2c_client *client)
{
      int err;
      struct max6875_data *data = i2c_get_clientdata(client);

      /* data is NULL for the fake client */
      if (data)
            sysfs_remove_bin_file(&client->dev.kobj, &user_eeprom_attr);

      err = i2c_detach_client(client);
      if (err)
            return err;

      if (data)         /* real client */
            kfree(data);
      else              /* fake client */
            kfree(client);
      return 0;
}

static int __init max6875_init(void)
{
      return i2c_add_driver(&max6875_driver);
}

static void __exit max6875_exit(void)
{
      i2c_del_driver(&max6875_driver);
}


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

module_init(max6875_init);
module_exit(max6875_exit);

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