// SPDX-License-Identifier: GPL-2.0
/*
 * IIO DAC emulation driver using a digital potentiometer
 *
 * Copyright (C) 2016 Axentia Technologies AB
 *
 * Author: Peter Rosin <peda@axentia.se>
 */

/*
 * 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/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. Say it again for GCC. */
                        fallthrough;
                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,
};

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->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))
                return dev_err_probe(&pdev->dev, PTR_ERR(dac->vref),
                                     "failed to get vref regulator\n");

        dac->dpot = devm_iio_channel_get(dev, "dpot");
        if (IS_ERR(dac->dpot))
                return dev_err_probe(&pdev->dev, PTR_ERR(dac->dpot),
                                     "failed to get dpot input channel\n");

        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 void 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);
}

static const struct of_device_id dpot_dac_match[] = {
        { .compatible = "dpot-dac" },
        { }
};
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");