/*
 * ltc2485.c - Driver for Linear Technology LTC2485 ADC
 *
 * Copyright (C) 2016 Alison Schofield <amsfield22@gmail.com>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Datasheet: http://cds.linear.com/docs/en/datasheet/2485fd.pdf
 */

#include <linux/delay.h>
#include <linux/i2c.h>
#include <linux/module.h>

#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>

/* Power-on configuration: rejects both 50/60Hz, operates at 1x speed */
#define LTC2485_CONFIG_DEFAULT		0

struct ltc2485_data {
	struct i2c_client	*client;
	ktime_t			time_prev;	/* last conversion */
};

static void ltc2485_wait_conv(struct ltc2485_data *data)
{
	const unsigned int conv_time = 147;	/* conversion time ms */
	unsigned int time_elapsed;

	/* delay if conversion time not passed since last read or write */
	time_elapsed = ktime_ms_delta(ktime_get(), data->time_prev);

	if (time_elapsed < conv_time)
		msleep(conv_time - time_elapsed);
}

static int ltc2485_read(struct ltc2485_data *data, int *val)
{
	struct i2c_client *client = data->client;
	__be32 buf = 0;
	int ret;

	ltc2485_wait_conv(data);

	ret = i2c_master_recv(client, (char *)&buf, 4);
	if (ret < 0)  {
		dev_err(&client->dev, "i2c_master_recv failed\n");
		return ret;
	}
	data->time_prev = ktime_get();
	*val = sign_extend32(be32_to_cpu(buf) >> 6, 24);

	return ret;
}

static int ltc2485_read_raw(struct iio_dev *indio_dev,
			    struct iio_chan_spec const *chan,
			    int *val, int *val2, long mask)
{
	struct ltc2485_data *data = iio_priv(indio_dev);
	int ret;

	if (mask == IIO_CHAN_INFO_RAW) {
		ret = ltc2485_read(data, val);
		if (ret < 0)
			return ret;

		return IIO_VAL_INT;

	} else if (mask == IIO_CHAN_INFO_SCALE) {
		*val = 5000;			/* on board vref millivolts */
		*val2 = 25;			/* 25 (24 + sign) data bits */
		return IIO_VAL_FRACTIONAL_LOG2;

	} else {
		return -EINVAL;
	}
}

static const struct iio_chan_spec ltc2485_channel[] = {
	{
		.type = IIO_VOLTAGE,
		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
		.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE)
	},
};

static const struct iio_info ltc2485_info = {
	.read_raw = ltc2485_read_raw,
	.driver_module = THIS_MODULE,
};

static int ltc2485_probe(struct i2c_client *client,
			 const struct i2c_device_id *id)
{
	struct iio_dev *indio_dev;
	struct ltc2485_data *data;
	int ret;

	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C |
				     I2C_FUNC_SMBUS_WRITE_BYTE))
		return -EOPNOTSUPP;

	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
	if (!indio_dev)
		return -ENOMEM;

	data = iio_priv(indio_dev);
	i2c_set_clientdata(client, indio_dev);
	data->client = client;

	indio_dev->dev.parent = &client->dev;
	indio_dev->name = id->name;
	indio_dev->info = &ltc2485_info;
	indio_dev->modes = INDIO_DIRECT_MODE;
	indio_dev->channels = ltc2485_channel;
	indio_dev->num_channels = ARRAY_SIZE(ltc2485_channel);

	ret = i2c_smbus_write_byte(data->client, LTC2485_CONFIG_DEFAULT);
	if (ret < 0)
		return ret;

	data->time_prev = ktime_get();

	return devm_iio_device_register(&client->dev, indio_dev);
}

static const struct i2c_device_id ltc2485_id[] = {
	{ "ltc2485", 0 },
	{ }
};
MODULE_DEVICE_TABLE(i2c, ltc2485_id);

static struct i2c_driver ltc2485_driver = {
	.driver = {
		.name = "ltc2485",
	},
	.probe = ltc2485_probe,
	.id_table = ltc2485_id,
};
module_i2c_driver(ltc2485_driver);

MODULE_AUTHOR("Alison Schofield <amsfield22@gmail.com>");
MODULE_DESCRIPTION("Linear Technology LTC2485 ADC driver");
MODULE_LICENSE("GPL v2");