// SPDX-License-Identifier: GPL-2.0
/*
 * The LTC2309 is an 8-Channel, 12-Bit SAR ADC with an I2C Interface.
 *
 * Datasheet:
 * https://www.analog.com/media/en/technical-documentation/data-sheets/2309fd.pdf
 *
 * Copyright (c) 2023, Liam Beguin <liambeguin@gmail.com>
 */
#include <linux/bitfield.h>
#include <linux/i2c.h>
#include <linux/iio/iio.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/regulator/consumer.h>

#define LTC2309_ADC_RESOLUTION  12
#define LTC2309_INTERNAL_REF_MV 4096

#define LTC2309_DIN_CH_MASK     GENMASK(7, 4)
#define LTC2309_DIN_SDN         BIT(7)
#define LTC2309_DIN_OSN         BIT(6)
#define LTC2309_DIN_S1          BIT(5)
#define LTC2309_DIN_S0          BIT(4)
#define LTC2309_DIN_UNI         BIT(3)
#define LTC2309_DIN_SLEEP       BIT(2)

/**
 * struct ltc2309 - internal device data structure
 * @dev:        Device reference
 * @client:     I2C reference
 * @lock:       Lock to serialize data access
 * @vref_mv:    Internal voltage reference
 */
struct ltc2309 {
        struct device           *dev;
        struct i2c_client       *client;
        struct mutex            lock; /* serialize data access */
        int                     vref_mv;
};

/* Order matches expected channel address, See datasheet Table 1. */
enum ltc2309_channels {
        LTC2309_CH0_CH1 = 0,
        LTC2309_CH2_CH3,
        LTC2309_CH4_CH5,
        LTC2309_CH6_CH7,
        LTC2309_CH1_CH0,
        LTC2309_CH3_CH2,
        LTC2309_CH5_CH4,
        LTC2309_CH7_CH6,
        LTC2309_CH0,
        LTC2309_CH2,
        LTC2309_CH4,
        LTC2309_CH6,
        LTC2309_CH1,
        LTC2309_CH3,
        LTC2309_CH5,
        LTC2309_CH7,
};

#define LTC2309_CHAN(_chan, _addr) {                            \
        .type = IIO_VOLTAGE,                                    \
        .indexed = 1,                                           \
        .address = _addr,                                       \
        .channel = _chan,                                       \
        .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),           \
        .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),   \
}

#define LTC2309_DIFF_CHAN(_chan, _chan2, _addr) {               \
        .type = IIO_VOLTAGE,                                    \
        .differential = 1,                                      \
        .indexed = 1,                                           \
        .address = _addr,                                       \
        .channel = _chan,                                       \
        .channel2 = _chan2,                                     \
        .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),           \
        .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),   \
}

static const struct iio_chan_spec ltc2309_channels[] = {
        LTC2309_CHAN(0, LTC2309_CH0),
        LTC2309_CHAN(1, LTC2309_CH1),
        LTC2309_CHAN(2, LTC2309_CH2),
        LTC2309_CHAN(3, LTC2309_CH3),
        LTC2309_CHAN(4, LTC2309_CH4),
        LTC2309_CHAN(5, LTC2309_CH5),
        LTC2309_CHAN(6, LTC2309_CH6),
        LTC2309_CHAN(7, LTC2309_CH7),
        LTC2309_DIFF_CHAN(0, 1, LTC2309_CH0_CH1),
        LTC2309_DIFF_CHAN(2, 3, LTC2309_CH2_CH3),
        LTC2309_DIFF_CHAN(4, 5, LTC2309_CH4_CH5),
        LTC2309_DIFF_CHAN(6, 7, LTC2309_CH6_CH7),
        LTC2309_DIFF_CHAN(1, 0, LTC2309_CH1_CH0),
        LTC2309_DIFF_CHAN(3, 2, LTC2309_CH3_CH2),
        LTC2309_DIFF_CHAN(5, 4, LTC2309_CH5_CH4),
        LTC2309_DIFF_CHAN(7, 6, LTC2309_CH7_CH6),
};

static int ltc2309_read_raw_channel(struct ltc2309 *ltc2309,
                                    unsigned long address, int *val)
{
        int ret;
        __be16 buf;
        u8 din;

        din = FIELD_PREP(LTC2309_DIN_CH_MASK, address & 0x0f) |
                FIELD_PREP(LTC2309_DIN_UNI, 1) |
                FIELD_PREP(LTC2309_DIN_SLEEP, 0);

        ret = i2c_smbus_write_byte(ltc2309->client, din);
        if (ret < 0) {
                dev_err(ltc2309->dev, "i2c command failed: %pe\n",
                        ERR_PTR(ret));
                return ret;
        }

        ret = i2c_master_recv(ltc2309->client, (char *)&buf, 2);
        if (ret < 0) {
                dev_err(ltc2309->dev, "i2c read failed: %pe\n", ERR_PTR(ret));
                return ret;
        }

        *val = be16_to_cpu(buf) >> 4;

        return ret;
}

static int ltc2309_read_raw(struct iio_dev *indio_dev,
                            struct iio_chan_spec const *chan, int *val,
                            int *val2, long mask)
{
        struct ltc2309 *ltc2309 = iio_priv(indio_dev);
        int ret;

        switch (mask) {
        case IIO_CHAN_INFO_RAW:
                mutex_lock(&ltc2309->lock);
                ret = ltc2309_read_raw_channel(ltc2309, chan->address, val);
                mutex_unlock(&ltc2309->lock);
                if (ret < 0)
                        return -EINVAL;
                return IIO_VAL_INT;
        case IIO_CHAN_INFO_SCALE:
                *val = ltc2309->vref_mv;
                *val2 = LTC2309_ADC_RESOLUTION;
                return IIO_VAL_FRACTIONAL_LOG2;
        default:
                return -EINVAL;
        }
}

static const struct iio_info ltc2309_info = {
        .read_raw = ltc2309_read_raw,
};

static int ltc2309_probe(struct i2c_client *client)
{
        struct iio_dev *indio_dev;
        struct ltc2309 *ltc2309;
        int ret;

        indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*ltc2309));
        if (!indio_dev)
                return -ENOMEM;

        ltc2309 = iio_priv(indio_dev);
        ltc2309->dev = &indio_dev->dev;
        ltc2309->client = client;

        indio_dev->name = "ltc2309";
        indio_dev->modes = INDIO_DIRECT_MODE;
        indio_dev->channels = ltc2309_channels;
        indio_dev->num_channels = ARRAY_SIZE(ltc2309_channels);
        indio_dev->info = &ltc2309_info;

        ret = devm_regulator_get_enable_read_voltage(&client->dev, "vref");
        if (ret < 0 && ret != -ENODEV)
                return dev_err_probe(ltc2309->dev, ret,
                                     "failed to get vref voltage\n");

        ltc2309->vref_mv = ret == -ENODEV ? LTC2309_INTERNAL_REF_MV : ret / 1000;

        mutex_init(&ltc2309->lock);

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

static const struct of_device_id ltc2309_of_match[] = {
        { .compatible = "lltc,ltc2309" },
        { }
};
MODULE_DEVICE_TABLE(of, ltc2309_of_match);

static const struct i2c_device_id ltc2309_id[] = {
        { "ltc2309" },
        { }
};
MODULE_DEVICE_TABLE(i2c, ltc2309_id);

static struct i2c_driver ltc2309_driver = {
        .driver = {
                .name = "ltc2309",
                .of_match_table = ltc2309_of_match,
        },
        .probe          = ltc2309_probe,
        .id_table       = ltc2309_id,
};
module_i2c_driver(ltc2309_driver);

MODULE_AUTHOR("Liam Beguin <liambeguin@gmail.com>");
MODULE_DESCRIPTION("Linear Technology LTC2309 ADC");
MODULE_LICENSE("GPL v2");