/*
   * I2C slave mode EEPROM simulator
   *
   * Copyright (C) 2014 by Wolfram Sang, Sang Engineering <wsa@sang-engineering.com>
   * Copyright (C) 2014 by Renesas Electronics Corporation
   *
   * 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.
   *
   * Because most IP blocks can only detect one I2C slave address anyhow, this
   * driver does not support simulating EEPROM types which take more than one
   * address. It is prepared to simulate bigger EEPROMs with an internal 16 bit
   * pointer, yet implementation is deferred until the need actually arises.
   */
  
  #include <linux/i2c.h>
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/of.h>
  #include <linux/slab.h>
  #include <linux/spinlock.h>
  #include <linux/sysfs.h>
  
  struct eeprom_data {
  	struct bin_attribute bin;
  	bool first_write;
  	spinlock_t buffer_lock;
  	u8 buffer_idx;
  	u8 buffer[];
  };
  
  static int i2c_slave_eeprom_slave_cb(struct i2c_client *client,
  				     enum i2c_slave_event event, u8 *val)
  {
  	struct eeprom_data *eeprom = i2c_get_clientdata(client);
  
  	switch (event) {

  	case I2C_SLAVE_WRITE_RECEIVED:

  		if (eeprom->first_write) {
  			eeprom->buffer_idx = *val;
  			eeprom->first_write = false;
  		} else {
  			spin_lock(&eeprom->buffer_lock);
  			eeprom->buffer[eeprom->buffer_idx++] = *val;
  			spin_unlock(&eeprom->buffer_lock);
  		}
  		break;

  	case I2C_SLAVE_READ_PROCESSED:

  		/* The previous byte made it to the bus, get next one */

  		eeprom->buffer_idx++;
  		/* fallthrough */
  	case I2C_SLAVE_READ_REQUESTED:

  		spin_lock(&eeprom->buffer_lock);
  		*val = eeprom->buffer[eeprom->buffer_idx];
  		spin_unlock(&eeprom->buffer_lock);

  		/*
  		 * Do not increment buffer_idx here, because we don't know if
  		 * this byte will be actually used. Read Linux I2C slave docs
  		 * for details.
  		 */

  		break;

  	case I2C_SLAVE_STOP:

  	case I2C_SLAVE_WRITE_REQUESTED:

  		eeprom->first_write = true;
  		break;
  
  	default:
  		break;
  	}
  
  	return 0;
  }
  
  static ssize_t i2c_slave_eeprom_bin_read(struct file *filp, struct kobject *kobj,
  		struct bin_attribute *attr, char *buf, loff_t off, size_t count)
  {
  	struct eeprom_data *eeprom;
  	unsigned long flags;

  	eeprom = dev_get_drvdata(container_of(kobj, struct device, kobj));
  
  	spin_lock_irqsave(&eeprom->buffer_lock, flags);
  	memcpy(buf, &eeprom->buffer[off], count);
  	spin_unlock_irqrestore(&eeprom->buffer_lock, flags);
  
  	return count;
  }
  
  static ssize_t i2c_slave_eeprom_bin_write(struct file *filp, struct kobject *kobj,
  		struct bin_attribute *attr, char *buf, loff_t off, size_t count)
  {
  	struct eeprom_data *eeprom;
  	unsigned long flags;

  	eeprom = dev_get_drvdata(container_of(kobj, struct device, kobj));
  
  	spin_lock_irqsave(&eeprom->buffer_lock, flags);
  	memcpy(&eeprom->buffer[off], buf, count);
  	spin_unlock_irqrestore(&eeprom->buffer_lock, flags);
  
  	return count;
  }
  
  static int i2c_slave_eeprom_probe(struct i2c_client *client, const struct i2c_device_id *id)
  {
  	struct eeprom_data *eeprom;
  	int ret;
  	unsigned size = id->driver_data;
  
  	eeprom = devm_kzalloc(&client->dev, sizeof(struct eeprom_data) + size, GFP_KERNEL);
  	if (!eeprom)
  		return -ENOMEM;
  
  	eeprom->first_write = true;
  	spin_lock_init(&eeprom->buffer_lock);
  	i2c_set_clientdata(client, eeprom);
  
  	sysfs_bin_attr_init(&eeprom->bin);
  	eeprom->bin.attr.name = "slave-eeprom";
  	eeprom->bin.attr.mode = S_IRUSR | S_IWUSR;
  	eeprom->bin.read = i2c_slave_eeprom_bin_read;
  	eeprom->bin.write = i2c_slave_eeprom_bin_write;
  	eeprom->bin.size = size;
  
  	ret = sysfs_create_bin_file(&client->dev.kobj, &eeprom->bin);
  	if (ret)
  		return ret;
  
  	ret = i2c_slave_register(client, i2c_slave_eeprom_slave_cb);
  	if (ret) {
  		sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
  		return ret;
  	}
  
  	return 0;
  };
  
  static int i2c_slave_eeprom_remove(struct i2c_client *client)
  {
  	struct eeprom_data *eeprom = i2c_get_clientdata(client);
  
  	i2c_slave_unregister(client);
  	sysfs_remove_bin_file(&client->dev.kobj, &eeprom->bin);
  
  	return 0;
  }
  
  static const struct i2c_device_id i2c_slave_eeprom_id[] = {
  	{ "slave-24c02", 2048 / 8 },
  	{ }
  };
  MODULE_DEVICE_TABLE(i2c, i2c_slave_eeprom_id);
  
  static struct i2c_driver i2c_slave_eeprom_driver = {
  	.driver = {
  		.name = "i2c-slave-eeprom",

  	},
  	.probe = i2c_slave_eeprom_probe,
  	.remove = i2c_slave_eeprom_remove,
  	.id_table = i2c_slave_eeprom_id,
  };
  module_i2c_driver(i2c_slave_eeprom_driver);
  
  MODULE_AUTHOR("Wolfram Sang <wsa@sang-engineering.com>");
  MODULE_DESCRIPTION("I2C slave mode EEPROM simulator");
  MODULE_LICENSE("GPL v2");