ltc4215.c

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/*
 * Driver for Linear Technology LTC4215 I2C Hot Swap Controller
 *
 * Copyright (C) 2009 Ira W. Snyder <[email protected]>
 *
 * 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\n");

        /* 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\n", 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\n", 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\n", power);
}

static ssize_t ltc4215_show_alarm(struct device *dev,
                      struct device_attribute *da,
                      char *buf)
{
    struct sensor_device_attribute_2 *attr = to_sensor_dev_attr_2(da);
    struct ltc4215_data *data = ltc4215_update_device(dev);
    const u8 reg = data->regs[attr->index];
    const u32 mask = attr->nr;

    return snprintf(buf, PAGE_SIZE, "%u\n", (reg & mask) ? 1 : 0);
}

/*
 * 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.
 */

#define LTC4215_VOLTAGE(name, ltc4215_cmd_idx) \
    static SENSOR_DEVICE_ATTR(name, S_IRUGO, \
    ltc4215_show_voltage, NULL, ltc4215_cmd_idx)

#define LTC4215_CURRENT(name) \
    static SENSOR_DEVICE_ATTR(name, S_IRUGO, \
    ltc4215_show_current, NULL, 0);

#define LTC4215_POWER(name) \
    static SENSOR_DEVICE_ATTR(name, S_IRUGO, \
    ltc4215_show_power, NULL, 0);

#define LTC4215_ALARM(name, mask, reg) \
    static SENSOR_DEVICE_ATTR_2(name, S_IRUGO, \
    ltc4215_show_alarm, NULL, (mask), reg)

/* Construct a sensor_device_attribute structure for each register */

/* Current */
LTC4215_CURRENT(curr1_input);
LTC4215_ALARM(curr1_max_alarm,  (1 << 2),   LTC4215_STATUS);

/* Power (virtual) */
LTC4215_POWER(power1_input);

/* Input Voltage */
LTC4215_VOLTAGE(in1_input,          LTC4215_ADIN);
LTC4215_ALARM(in1_max_alarm,    (1 << 0),   LTC4215_STATUS);
LTC4215_ALARM(in1_min_alarm,    (1 << 1),   LTC4215_STATUS);

/* Output Voltage */
LTC4215_VOLTAGE(in2_input,          LTC4215_SOURCE);
LTC4215_ALARM(in2_min_alarm,    (1 << 3),   LTC4215_STATUS);

/*
 * 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 <[email protected]>");
MODULE_DESCRIPTION("LTC4215 driver");
MODULE_LICENSE("GPL");