/*
 * IIO DAC emulation driver using a digital potentiometer
 *
 * Copyright (C) 2016 Axentia Technologies AB
 *
 * Author: Peter Rosin <peda@axentia.se>
 *
 * 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.
 */

/*
 * It is assumed that the dpot is used as a voltage divider between the
 * current dpot wiper setting and the maximum resistance of the dpot. The
 * divided voltage is provided by a vref regulator.
 *
 *                   .------.
 *    .-----------.  |      |
 *    | vref      |--'    .---.
 *    | regulator |--.    |   |
 *    '-----------'  |    | d |
 *                   |    | p |
 *                   |    | o |  wiper
 *                   |    | t |<---------+
 *                   |    |   |
 *                   |    '---'       dac output voltage
 *                   |      |
 *                   '------+------------+
 */

#include <linux/err.h>
#include <linux/iio/consumer.h>
#include <linux/iio/iio.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/regulator/consumer.h>

struct dpot_dac {
	struct regulator *vref;
	struct iio_channel *dpot;
	u32 max_ohms;
};

static const struct iio_chan_spec dpot_dac_iio_channel = {
	.type = IIO_VOLTAGE,
	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW)
			    | BIT(IIO_CHAN_INFO_SCALE),
	.info_mask_separate_available = BIT(IIO_CHAN_INFO_RAW),
	.output = 1,
	.indexed = 1,
};

static int dpot_dac_read_raw(struct iio_dev *indio_dev,
			     struct iio_chan_spec const *chan,
			     int *val, int *val2, long mask)
{
	struct dpot_dac *dac = iio_priv(indio_dev);
	int ret;
	unsigned long long tmp;

	switch (mask) {
	case IIO_CHAN_INFO_RAW:
		return iio_read_channel_raw(dac->dpot, val);

	case IIO_CHAN_INFO_SCALE:
		ret = iio_read_channel_scale(dac->dpot, val, val2);
		switch (ret) {
		case IIO_VAL_FRACTIONAL_LOG2:
			tmp = *val * 1000000000LL;
			do_div(tmp, dac->max_ohms);
			tmp *= regulator_get_voltage(dac->vref) / 1000;
			do_div(tmp, 1000000000LL);
			*val = tmp;
			return ret;
		case IIO_VAL_INT:
			/*
			 * Convert integer scale to fractional scale by
			 * setting the denominator (val2) to one...
			 */
			*val2 = 1;
			ret = IIO_VAL_FRACTIONAL;
			/* ...and fall through. */
		case IIO_VAL_FRACTIONAL:
			*val *= regulator_get_voltage(dac->vref) / 1000;
			*val2 *= dac->max_ohms;
			break;
		}

		return ret;
	}

	return -EINVAL;
}

static int dpot_dac_read_avail(struct iio_dev *indio_dev,
			       struct iio_chan_spec const *chan,
			       const int **vals, int *type, int *length,
			       long mask)
{
	struct dpot_dac *dac = iio_priv(indio_dev);

	switch (mask) {
	case IIO_CHAN_INFO_RAW:
		*type = IIO_VAL_INT;
		return iio_read_avail_channel_raw(dac->dpot, vals, length);
	}

	return -EINVAL;
}

static int dpot_dac_write_raw(struct iio_dev *indio_dev,
			      struct iio_chan_spec const *chan,
			      int val, int val2, long mask)
{
	struct dpot_dac *dac = iio_priv(indio_dev);

	switch (mask) {
	case IIO_CHAN_INFO_RAW:
		return iio_write_channel_raw(dac->dpot, val);
	}

	return -EINVAL;
}

static const struct iio_info dpot_dac_info = {
	.read_raw = dpot_dac_read_raw,
	.read_avail = dpot_dac_read_avail,
	.write_raw = dpot_dac_write_raw,
	.driver_module = THIS_MODULE,
};

static int dpot_dac_channel_max_ohms(struct iio_dev *indio_dev)
{
	struct device *dev = &indio_dev->dev;
	struct dpot_dac *dac = iio_priv(indio_dev);
	unsigned long long tmp;
	int ret;
	int val;
	int val2;
	int max;

	ret = iio_read_max_channel_raw(dac->dpot, &max);
	if (ret < 0) {
		dev_err(dev, "dpot does not indicate its raw maximum value\n");
		return ret;
	}

	switch (iio_read_channel_scale(dac->dpot, &val, &val2)) {
	case IIO_VAL_INT:
		return max * val;
	case IIO_VAL_FRACTIONAL:
		tmp = (unsigned long long)max * val;
		do_div(tmp, val2);
		return tmp;
	case IIO_VAL_FRACTIONAL_LOG2:
		tmp = val * 1000000000LL * max >> val2;
		do_div(tmp, 1000000000LL);
		return tmp;
	default:
		dev_err(dev, "dpot has a scale that is too weird\n");
	}

	return -EINVAL;
}

static int dpot_dac_probe(struct platform_device *pdev)
{
	struct device *dev = &pdev->dev;
	struct iio_dev *indio_dev;
	struct dpot_dac *dac;
	enum iio_chan_type type;
	int ret;

	indio_dev = devm_iio_device_alloc(dev, sizeof(*dac));
	if (!indio_dev)
		return -ENOMEM;

	platform_set_drvdata(pdev, indio_dev);
	dac = iio_priv(indio_dev);

	indio_dev->name = dev_name(dev);
	indio_dev->dev.parent = dev;
	indio_dev->info = &dpot_dac_info;
	indio_dev->modes = INDIO_DIRECT_MODE;
	indio_dev->channels = &dpot_dac_iio_channel;
	indio_dev->num_channels = 1;

	dac->vref = devm_regulator_get(dev, "vref");
	if (IS_ERR(dac->vref)) {
		if (PTR_ERR(dac->vref) != -EPROBE_DEFER)
			dev_err(&pdev->dev, "failed to get vref regulator\n");
		return PTR_ERR(dac->vref);
	}

	dac->dpot = devm_iio_channel_get(dev, "dpot");
	if (IS_ERR(dac->dpot)) {
		if (PTR_ERR(dac->dpot) != -EPROBE_DEFER)
			dev_err(dev, "failed to get dpot input channel\n");
		return PTR_ERR(dac->dpot);
	}

	ret = iio_get_channel_type(dac->dpot, &type);
	if (ret < 0)
		return ret;

	if (type != IIO_RESISTANCE) {
		dev_err(dev, "dpot is of the wrong type\n");
		return -EINVAL;
	}

	ret = dpot_dac_channel_max_ohms(indio_dev);
	if (ret < 0)
		return ret;
	dac->max_ohms = ret;

	ret = regulator_enable(dac->vref);
	if (ret) {
		dev_err(dev, "failed to enable the vref regulator\n");
		return ret;
	}

	ret = iio_device_register(indio_dev);
	if (ret) {
		dev_err(dev, "failed to register iio device\n");
		goto disable_reg;
	}

	return 0;

disable_reg:
	regulator_disable(dac->vref);
	return ret;
}

static int dpot_dac_remove(struct platform_device *pdev)
{
	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
	struct dpot_dac *dac = iio_priv(indio_dev);

	iio_device_unregister(indio_dev);
	regulator_disable(dac->vref);

	return 0;
}

static const struct of_device_id dpot_dac_match[] = {
	{ .compatible = "dpot-dac" },
	{ /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, dpot_dac_match);

static struct platform_driver dpot_dac_driver = {
	.probe = dpot_dac_probe,
	.remove = dpot_dac_remove,
	.driver = {
		.name = "iio-dpot-dac",
		.of_match_table = dpot_dac_match,
	},
};
module_platform_driver(dpot_dac_driver);

MODULE_DESCRIPTION("DAC emulation driver using a digital potentiometer");
MODULE_AUTHOR("Peter Rosin <peda@axentia.se>");
MODULE_LICENSE("GPL v2");