// SPDX-License-Identifier: GPL-2.0
/*
 * Sensirion SCD30 carbon dioxide sensor serial driver
 *
 * Copyright (c) 2020 Tomasz Duszynski <tomasz.duszynski@octakon.com>
 */
#include <linux/crc16.h>
#include <linux/device.h>
#include <linux/errno.h>
#include <linux/iio/iio.h>
#include <linux/jiffies.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/property.h>
#include <linux/serdev.h>
#include <linux/string.h>
#include <linux/types.h>
#include <linux/unaligned.h>

#include "scd30.h"

#define SCD30_SERDEV_ADDR 0x61
#define SCD30_SERDEV_WRITE 0x06
#define SCD30_SERDEV_READ 0x03
#define SCD30_SERDEV_MAX_BUF_SIZE 17
#define SCD30_SERDEV_RX_HEADER_SIZE 3
#define SCD30_SERDEV_CRC_SIZE 2
#define SCD30_SERDEV_TIMEOUT msecs_to_jiffies(200)

struct scd30_serdev_priv {
        struct completion meas_ready;
        char *buf;
        int num_expected;
        int num;
};

static u16 scd30_serdev_cmd_lookup_tbl[] = {
        [CMD_START_MEAS] = 0x0036,
        [CMD_STOP_MEAS] = 0x0037,
        [CMD_MEAS_INTERVAL] = 0x0025,
        [CMD_MEAS_READY] = 0x0027,
        [CMD_READ_MEAS] = 0x0028,
        [CMD_ASC] = 0x003a,
        [CMD_FRC] = 0x0039,
        [CMD_TEMP_OFFSET] = 0x003b,
        [CMD_FW_VERSION] = 0x0020,
        [CMD_RESET] = 0x0034,
};

static u16 scd30_serdev_calc_crc(const char *buf, int size)
{
        return crc16(0xffff, buf, size);
}

static int scd30_serdev_xfer(struct scd30_state *state, char *txbuf, int txsize,
                             char *rxbuf, int rxsize)
{
        struct serdev_device *serdev = to_serdev_device(state->dev);
        struct scd30_serdev_priv *priv = state->priv;
        int ret;

        priv->buf = rxbuf;
        priv->num_expected = rxsize;
        priv->num = 0;

        ret = serdev_device_write(serdev, txbuf, txsize, SCD30_SERDEV_TIMEOUT);
        if (ret < 0)
                return ret;
        if (ret != txsize)
                return -EIO;

        ret = wait_for_completion_interruptible_timeout(&priv->meas_ready, SCD30_SERDEV_TIMEOUT);
        if (ret < 0)
                return ret;
        if (!ret)
                return -ETIMEDOUT;

        return 0;
}

static int scd30_serdev_command(struct scd30_state *state, enum scd30_cmd cmd, u16 arg,
                                void *response, int size)
{
        /*
         * Communication over serial line is based on modbus protocol (or rather
         * its variation called modbus over serial to be precise). Upon
         * receiving a request device should reply with response.
         *
         * Frame below represents a request message. Each field takes
         * exactly one byte.
         *
         * +------+------+-----+-----+-------+-------+-----+-----+
         * | dev  | op   | reg | reg | byte1 | byte0 | crc | crc |
         * | addr | code | msb | lsb |       |       | lsb | msb |
         * +------+------+-----+-----+-------+-------+-----+-----+
         *
         * The message device replies with depends on the 'op code' field from
         * the request. In case it was set to SCD30_SERDEV_WRITE sensor should
         * reply with unchanged request. Otherwise 'op code' was set to
         * SCD30_SERDEV_READ and response looks like the one below. As with
         * request, each field takes one byte.
         *
         * +------+------+--------+-------+-----+-------+-----+-----+
         * | dev  | op   | num of | byte0 | ... | byteN | crc | crc |
         * | addr | code | bytes  |       |     |       | lsb | msb |
         * +------+------+--------+-------+-----+-------+-----+-----+
         */
        char txbuf[SCD30_SERDEV_MAX_BUF_SIZE] = { SCD30_SERDEV_ADDR },
             rxbuf[SCD30_SERDEV_MAX_BUF_SIZE];
        int ret, rxsize, txsize = 2;
        char *rsp = response;
        u16 crc;

        put_unaligned_be16(scd30_serdev_cmd_lookup_tbl[cmd], txbuf + txsize);
        txsize += 2;

        if (rsp) {
                txbuf[1] = SCD30_SERDEV_READ;
                if (cmd == CMD_READ_MEAS)
                        /* number of u16 words to read */
                        put_unaligned_be16(size / 2, txbuf + txsize);
                else
                        put_unaligned_be16(0x0001, txbuf + txsize);
                txsize += 2;
                crc = scd30_serdev_calc_crc(txbuf, txsize);
                put_unaligned_le16(crc, txbuf + txsize);
                txsize += 2;
                rxsize = SCD30_SERDEV_RX_HEADER_SIZE + size + SCD30_SERDEV_CRC_SIZE;
        } else {
                if ((cmd == CMD_STOP_MEAS) || (cmd == CMD_RESET))
                        arg = 0x0001;

                txbuf[1] = SCD30_SERDEV_WRITE;
                put_unaligned_be16(arg, txbuf + txsize);
                txsize += 2;
                crc = scd30_serdev_calc_crc(txbuf, txsize);
                put_unaligned_le16(crc, txbuf + txsize);
                txsize += 2;
                rxsize = txsize;
        }

        ret = scd30_serdev_xfer(state, txbuf, txsize, rxbuf, rxsize);
        if (ret)
                return ret;

        switch (txbuf[1]) {
        case SCD30_SERDEV_WRITE:
                if (memcmp(txbuf, rxbuf, txsize)) {
                        dev_err(state->dev, "wrong message received\n");
                        return -EIO;
                }
                break;
        case SCD30_SERDEV_READ:
                if (rxbuf[2] != (rxsize - SCD30_SERDEV_RX_HEADER_SIZE - SCD30_SERDEV_CRC_SIZE)) {
                        dev_err(state->dev, "received data size does not match header\n");
                        return -EIO;
                }

                rxsize -= SCD30_SERDEV_CRC_SIZE;
                crc = get_unaligned_le16(rxbuf + rxsize);
                if (crc != scd30_serdev_calc_crc(rxbuf, rxsize)) {
                        dev_err(state->dev, "data integrity check failed\n");
                        return -EIO;
                }

                rxsize -= SCD30_SERDEV_RX_HEADER_SIZE;
                memcpy(rsp, rxbuf + SCD30_SERDEV_RX_HEADER_SIZE, rxsize);
                break;
        default:
                dev_err(state->dev, "received unknown op code\n");
                return -EIO;
        }

        return 0;
}

static size_t scd30_serdev_receive_buf(struct serdev_device *serdev,
                                       const u8 *buf, size_t size)
{
        struct iio_dev *indio_dev = serdev_device_get_drvdata(serdev);
        struct scd30_serdev_priv *priv;
        struct scd30_state *state;
        size_t num;

        if (!indio_dev)
                return 0;

        state = iio_priv(indio_dev);
        priv = state->priv;

        /* just in case sensor puts some unexpected bytes on the bus */
        if (!priv->buf)
                return 0;

        if (priv->num + size >= priv->num_expected)
                num = priv->num_expected - priv->num;
        else
                num = size;

        memcpy(priv->buf + priv->num, buf, num);
        priv->num += num;

        if (priv->num == priv->num_expected) {
                priv->buf = NULL;
                complete(&priv->meas_ready);
        }

        return num;
}

static const struct serdev_device_ops scd30_serdev_ops = {
        .receive_buf = scd30_serdev_receive_buf,
        .write_wakeup = serdev_device_write_wakeup,
};

static int scd30_serdev_probe(struct serdev_device *serdev)
{
        struct device *dev = &serdev->dev;
        struct scd30_serdev_priv *priv;
        int irq, ret;

        priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        init_completion(&priv->meas_ready);
        serdev_device_set_client_ops(serdev, &scd30_serdev_ops);

        ret = devm_serdev_device_open(dev, serdev);
        if (ret)
                return ret;

        serdev_device_set_baudrate(serdev, 19200);
        serdev_device_set_flow_control(serdev, false);

        ret = serdev_device_set_parity(serdev, SERDEV_PARITY_NONE);
        if (ret)
                return ret;

        irq = fwnode_irq_get(dev_fwnode(dev), 0);

        return scd30_probe(dev, irq, KBUILD_MODNAME, priv, scd30_serdev_command);
}

static const struct of_device_id scd30_serdev_of_match[] = {
        { .compatible = "sensirion,scd30" },
        { }
};
MODULE_DEVICE_TABLE(of, scd30_serdev_of_match);

static struct serdev_device_driver scd30_serdev_driver = {
        .driver = {
                .name = KBUILD_MODNAME,
                .of_match_table = scd30_serdev_of_match,
                .pm = pm_sleep_ptr(&scd30_pm_ops),
        },
        .probe = scd30_serdev_probe,
};
module_serdev_device_driver(scd30_serdev_driver);

MODULE_AUTHOR("Tomasz Duszynski <tomasz.duszynski@octakon.com>");
MODULE_DESCRIPTION("Sensirion SCD30 carbon dioxide sensor serial driver");
MODULE_LICENSE("GPL v2");
MODULE_IMPORT_NS("IIO_SCD30");