/*
   * Driver for Linear Technology LTC4215 I2C Hot Swap Controller
   *
   * Copyright (C) 2009 Ira W. Snyder <iws@ovro.caltech.edu>
   *
   * 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.
   *
   * Datasheet:
   * http://www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1006,C1163,P17572,D12697
   */
  
  #include <linux/kernel.h>
  #include <linux/module.h>
  #include <linux/init.h>
  #include <linux/err.h>
  #include <linux/slab.h>
  #include <linux/i2c.h>
  #include <linux/hwmon.h>
  #include <linux/hwmon-sysfs.h>
  #include <linux/jiffies.h>
  
  /* Here are names of the chip's registers (a.k.a. commands) */
  enum ltc4215_cmd {
  	LTC4215_CONTROL			= 0x00, /* rw */
  	LTC4215_ALERT			= 0x01, /* rw */
  	LTC4215_STATUS			= 0x02, /* ro */
  	LTC4215_FAULT			= 0x03, /* rw */
  	LTC4215_SENSE			= 0x04, /* rw */
  	LTC4215_SOURCE			= 0x05, /* rw */
  	LTC4215_ADIN			= 0x06, /* rw */
  };
  
  struct ltc4215_data {
  	struct device *hwmon_dev;
  
  	struct mutex update_lock;
  	bool valid;
  	unsigned long last_updated; /* in jiffies */
  
  	/* Registers */
  	u8 regs[7];
  };
  
  static struct ltc4215_data *ltc4215_update_device(struct device *dev)
  {
  	struct i2c_client *client = to_i2c_client(dev);
  	struct ltc4215_data *data = i2c_get_clientdata(client);
  	s32 val;
  	int i;
  
  	mutex_lock(&data->update_lock);
  
  	/* The chip's A/D updates 10 times per second */
  	if (time_after(jiffies, data->last_updated + HZ / 10) || !data->valid) {
  
  		dev_dbg(&client->dev, "Starting ltc4215 update
  ");
  
  		/* Read all registers */
  		for (i = 0; i < ARRAY_SIZE(data->regs); i++) {
  			val = i2c_smbus_read_byte_data(client, i);
  			if (unlikely(val < 0))
  				data->regs[i] = 0;
  			else
  				data->regs[i] = val;
  		}
  
  		data->last_updated = jiffies;
  		data->valid = 1;
  	}
  
  	mutex_unlock(&data->update_lock);
  
  	return data;
  }
  
  /* Return the voltage from the given register in millivolts */
  static int ltc4215_get_voltage(struct device *dev, u8 reg)
  {
  	struct ltc4215_data *data = ltc4215_update_device(dev);
  	const u8 regval = data->regs[reg];
  	u32 voltage = 0;
  
  	switch (reg) {
  	case LTC4215_SENSE:
  		/* 151 uV per increment */
  		voltage = regval * 151 / 1000;
  		break;
  	case LTC4215_SOURCE:
  		/* 60.5 mV per increment */
  		voltage = regval * 605 / 10;
  		break;
  	case LTC4215_ADIN:
  		/*
  		 * The ADIN input is divided by 12.5, and has 4.82 mV
  		 * per increment, so we have the additional multiply
  		 */
  		voltage = regval * 482 * 125 / 1000;
  		break;
  	default:
  		/* If we get here, the developer messed up */
  		WARN_ON_ONCE(1);
  		break;
  	}
  
  	return voltage;
  }
  
  /* Return the current from the sense resistor in mA */
  static unsigned int ltc4215_get_current(struct device *dev)
  {
  	struct ltc4215_data *data = ltc4215_update_device(dev);
  
  	/*
  	 * The strange looking conversions that follow are fixed-point
  	 * math, since we cannot do floating point in the kernel.
  	 *
  	 * Step 1: convert sense register to microVolts
  	 * Step 2: convert voltage to milliAmperes
  	 *
  	 * If you play around with the V=IR equation, you come up with
  	 * the following: X uV / Y mOhm == Z mA
  	 *
  	 * With the resistors that are fractions of a milliOhm, we multiply
  	 * the voltage and resistance by 10, to shift the decimal point.
  	 * Now we can use the normal division operator again.
  	 */
  
  	/* Calculate voltage in microVolts (151 uV per increment) */
  	const unsigned int voltage = data->regs[LTC4215_SENSE] * 151;
  
  	/* Calculate current in milliAmperes (4 milliOhm sense resistor) */
  	const unsigned int curr = voltage / 4;
  
  	return curr;
  }
  
  static ssize_t ltc4215_show_voltage(struct device *dev,
  				    struct device_attribute *da,
  				    char *buf)
  {
  	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
  	const int voltage = ltc4215_get_voltage(dev, attr->index);
  
  	return snprintf(buf, PAGE_SIZE, "%d
  ", voltage);
  }
  
  static ssize_t ltc4215_show_current(struct device *dev,
  				    struct device_attribute *da,
  				    char *buf)
  {
  	const unsigned int curr = ltc4215_get_current(dev);
  
  	return snprintf(buf, PAGE_SIZE, "%u
  ", curr);
  }
  
  static ssize_t ltc4215_show_power(struct device *dev,
  				  struct device_attribute *da,
  				  char *buf)
  {
  	const unsigned int curr = ltc4215_get_current(dev);
  	const int output_voltage = ltc4215_get_voltage(dev, LTC4215_ADIN);
  
  	/* current in mA * voltage in mV == power in uW */
  	const unsigned int power = abs(output_voltage * curr);
  
  	return snprintf(buf, PAGE_SIZE, "%u
  ", power);
  }
  
  static ssize_t ltc4215_show_alarm(struct device *dev,
  					  struct device_attribute *da,
  					  char *buf)
  {
  	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
  	struct ltc4215_data *data = ltc4215_update_device(dev);
  	const u8 reg = data->regs[LTC4215_STATUS];
  	const u32 mask = attr->index;
  
  	return snprintf(buf, PAGE_SIZE, "%u
  ", !!(reg & mask));
  }
  
  /*
   * These macros are used below in constructing device attribute objects
   * for use with sysfs_create_group() to make a sysfs device file
   * for each register.
   */
  
  /* Construct a sensor_device_attribute structure for each register */
  
  /* Current */
  static SENSOR_DEVICE_ATTR(curr1_input, S_IRUGO, ltc4215_show_current, NULL, 0);
  static SENSOR_DEVICE_ATTR(curr1_max_alarm, S_IRUGO, ltc4215_show_alarm, NULL,
  			  1 << 2);
  
  /* Power (virtual) */
  static SENSOR_DEVICE_ATTR(power1_input, S_IRUGO, ltc4215_show_power, NULL, 0);
  
  /* Input Voltage */
  static SENSOR_DEVICE_ATTR(in1_input, S_IRUGO, ltc4215_show_voltage, NULL,
  			  LTC4215_ADIN);
  static SENSOR_DEVICE_ATTR(in1_max_alarm, S_IRUGO, ltc4215_show_alarm, NULL,
  			  1 << 0);
  static SENSOR_DEVICE_ATTR(in1_min_alarm, S_IRUGO, ltc4215_show_alarm, NULL,
  			  1 << 1);
  
  /* Output Voltage */
  static SENSOR_DEVICE_ATTR(in2_input, S_IRUGO, ltc4215_show_voltage, NULL,
  			  LTC4215_SOURCE);
  static SENSOR_DEVICE_ATTR(in2_min_alarm, S_IRUGO, ltc4215_show_alarm, NULL,
  			  1 << 3);
  
  /*
   * Finally, construct an array of pointers to members of the above objects,
   * as required for sysfs_create_group()
   */
  static struct attribute *ltc4215_attributes[] = {
  	&sensor_dev_attr_curr1_input.dev_attr.attr,
  	&sensor_dev_attr_curr1_max_alarm.dev_attr.attr,
  
  	&sensor_dev_attr_power1_input.dev_attr.attr,
  
  	&sensor_dev_attr_in1_input.dev_attr.attr,
  	&sensor_dev_attr_in1_max_alarm.dev_attr.attr,
  	&sensor_dev_attr_in1_min_alarm.dev_attr.attr,
  
  	&sensor_dev_attr_in2_input.dev_attr.attr,
  	&sensor_dev_attr_in2_min_alarm.dev_attr.attr,
  
  	NULL,
  };
  
  static const struct attribute_group ltc4215_group = {
  	.attrs = ltc4215_attributes,
  };
  
  static int ltc4215_probe(struct i2c_client *client,
  			 const struct i2c_device_id *id)
  {
  	struct i2c_adapter *adapter = client->adapter;
  	struct ltc4215_data *data;
  	int ret;
  
  	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA))
  		return -ENODEV;
  
  	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
  	if (!data)
  		return -ENOMEM;
  
  	i2c_set_clientdata(client, data);
  	mutex_init(&data->update_lock);
  
  	/* Initialize the LTC4215 chip */
  	i2c_smbus_write_byte_data(client, LTC4215_FAULT, 0x00);
  
  	/* Register sysfs hooks */
  	ret = sysfs_create_group(&client->dev.kobj, &ltc4215_group);
  	if (ret)
  		return ret;
  
  	data->hwmon_dev = hwmon_device_register(&client->dev);
  	if (IS_ERR(data->hwmon_dev)) {
  		ret = PTR_ERR(data->hwmon_dev);
  		goto out_hwmon_device_register;
  	}
  
  	return 0;
  
  out_hwmon_device_register:
  	sysfs_remove_group(&client->dev.kobj, &ltc4215_group);
  	return ret;
  }
  
  static int ltc4215_remove(struct i2c_client *client)
  {
  	struct ltc4215_data *data = i2c_get_clientdata(client);
  
  	hwmon_device_unregister(data->hwmon_dev);
  	sysfs_remove_group(&client->dev.kobj, &ltc4215_group);
  
  	return 0;
  }
  
  static const struct i2c_device_id ltc4215_id[] = {
  	{ "ltc4215", 0 },
  	{ }
  };
  MODULE_DEVICE_TABLE(i2c, ltc4215_id);
  
  /* This is the driver that will be inserted */
  static struct i2c_driver ltc4215_driver = {
  	.driver = {
  		.name	= "ltc4215",
  	},
  	.probe		= ltc4215_probe,
  	.remove		= ltc4215_remove,
  	.id_table	= ltc4215_id,
  };
  
  module_i2c_driver(ltc4215_driver);
  
  MODULE_AUTHOR("Ira W. Snyder <iws@ovro.caltech.edu>");
  MODULE_DESCRIPTION("LTC4215 driver");
  MODULE_LICENSE("GPL");