// SPDX-License-Identifier: GPL-2.0-only
/*
 * Aosong AM2315 relative humidity and temperature
 *
 * Copyright (c) 2016, Intel Corporation.
 *
 * 7-bit I2C address: 0x5C.
 */

#include <linux/delay.h>
#include <linux/i2c.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/iio/buffer.h>
#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>
#include <linux/iio/trigger_consumer.h>
#include <linux/iio/triggered_buffer.h>

#define AM2315_REG_HUM_MSB                      0x00
#define AM2315_REG_HUM_LSB                      0x01
#define AM2315_REG_TEMP_MSB                     0x02
#define AM2315_REG_TEMP_LSB                     0x03

#define AM2315_FUNCTION_READ                    0x03
#define AM2315_HUM_OFFSET                       2
#define AM2315_TEMP_OFFSET                      4
#define AM2315_ALL_CHANNEL_MASK                 GENMASK(1, 0)

#define AM2315_DRIVER_NAME                      "am2315"

struct am2315_data {
        struct i2c_client *client;
        struct mutex lock;
        /* Ensure timestamp is naturally aligned */
        struct {
                s16 chans[2];
                aligned_s64 timestamp;
        } scan;
};

struct am2315_sensor_data {
        s16 hum_data;
        s16 temp_data;
};

static const struct iio_chan_spec am2315_channels[] = {
        {
                .type = IIO_HUMIDITYRELATIVE,
                .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
                                      BIT(IIO_CHAN_INFO_SCALE),
                .scan_index = 0,
                .scan_type = {
                        .sign = 's',
                        .realbits = 16,
                        .storagebits = 16,
                        .endianness = IIO_CPU,
                },
        },
        {
                .type = IIO_TEMP,
                .info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
                                      BIT(IIO_CHAN_INFO_SCALE),
                .scan_index = 1,
                .scan_type = {
                        .sign = 's',
                        .realbits = 16,
                        .storagebits = 16,
                        .endianness = IIO_CPU,
                },
        },
        IIO_CHAN_SOFT_TIMESTAMP(2),
};

/* CRC calculation algorithm, as specified in the datasheet (page 13). */
static u16 am2315_crc(u8 *data, u8 nr_bytes)
{
        int i;
        u16 crc = 0xffff;

        while (nr_bytes--) {
                crc ^= *data++;
                for (i = 0; i < 8; i++) {
                        if (crc & 0x01) {
                                crc >>= 1;
                                crc ^= 0xA001;
                        } else {
                                crc >>= 1;
                        }
                }
        }

        return crc;
}

/* Simple function that sends a few bytes to the device to wake it up. */
static void am2315_ping(struct i2c_client *client)
{
        i2c_smbus_read_byte_data(client, AM2315_REG_HUM_MSB);
}

static int am2315_read_data(struct am2315_data *data,
                            struct am2315_sensor_data *sensor_data)
{
        int ret;
        /* tx_buf format: <function code> <start addr> <nr of regs to read> */
        u8 tx_buf[3] = { AM2315_FUNCTION_READ, AM2315_REG_HUM_MSB, 4 };
        /*
         * rx_buf format:
         * <function code> <number of registers read>
         * <humidity MSB> <humidity LSB> <temp MSB> <temp LSB>
         * <CRC LSB> <CRC MSB>
         */
        u8 rx_buf[8];
        u16 crc;

        /* First wake up the device. */
        am2315_ping(data->client);

        mutex_lock(&data->lock);
        ret = i2c_master_send(data->client, tx_buf, sizeof(tx_buf));
        if (ret < 0) {
                dev_err(&data->client->dev, "failed to send read request\n");
                goto exit_unlock;
        }
        /* Wait 2-3 ms, then read back the data sent by the device. */
        usleep_range(2000, 3000);
        /* Do a bulk data read, then pick out what we need. */
        ret = i2c_master_recv(data->client, rx_buf, sizeof(rx_buf));
        if (ret < 0) {
                dev_err(&data->client->dev, "failed to read sensor data\n");
                goto exit_unlock;
        }
        mutex_unlock(&data->lock);
        /*
         * Do a CRC check on the data and compare it to the value
         * calculated by the device.
         */
        crc = am2315_crc(rx_buf, sizeof(rx_buf) - 2);
        if ((crc & 0xff) != rx_buf[6] || (crc >> 8) != rx_buf[7]) {
                dev_err(&data->client->dev, "failed to verify sensor data\n");
                return -EIO;
        }

        sensor_data->hum_data = (rx_buf[AM2315_HUM_OFFSET] << 8) |
                                 rx_buf[AM2315_HUM_OFFSET + 1];
        sensor_data->temp_data = (rx_buf[AM2315_TEMP_OFFSET] << 8) |
                                  rx_buf[AM2315_TEMP_OFFSET + 1];

        return ret;

exit_unlock:
        mutex_unlock(&data->lock);
        return ret;
}

static irqreturn_t am2315_trigger_handler(int irq, void *p)
{
        int i;
        int ret;
        int bit;
        struct iio_poll_func *pf = p;
        struct iio_dev *indio_dev = pf->indio_dev;
        struct am2315_data *data = iio_priv(indio_dev);
        struct am2315_sensor_data sensor_data;

        ret = am2315_read_data(data, &sensor_data);
        if (ret < 0)
                goto err;

        mutex_lock(&data->lock);
        if (*(indio_dev->active_scan_mask) == AM2315_ALL_CHANNEL_MASK) {
                data->scan.chans[0] = sensor_data.hum_data;
                data->scan.chans[1] = sensor_data.temp_data;
        } else {
                i = 0;
                iio_for_each_active_channel(indio_dev, bit) {
                        data->scan.chans[i] = (bit ? sensor_data.temp_data :
                                               sensor_data.hum_data);
                        i++;
                }
        }
        mutex_unlock(&data->lock);

        iio_push_to_buffers_with_timestamp(indio_dev, &data->scan,
                                           pf->timestamp);
err:
        iio_trigger_notify_done(indio_dev->trig);
        return IRQ_HANDLED;
}

static int am2315_read_raw(struct iio_dev *indio_dev,
                           struct iio_chan_spec const *chan,
                           int *val, int *val2, long mask)
{
        int ret;
        struct am2315_sensor_data sensor_data;
        struct am2315_data *data = iio_priv(indio_dev);

        switch (mask) {
        case IIO_CHAN_INFO_RAW:
                ret = am2315_read_data(data, &sensor_data);
                if (ret < 0)
                        return ret;
                *val = (chan->type == IIO_HUMIDITYRELATIVE) ?
                                sensor_data.hum_data : sensor_data.temp_data;
                return IIO_VAL_INT;
        case IIO_CHAN_INFO_SCALE:
                *val = 100;
                return IIO_VAL_INT;
        }

        return -EINVAL;
}

static const struct iio_info am2315_info = {
        .read_raw               = am2315_read_raw,
};

static int am2315_probe(struct i2c_client *client)
{
        int ret;
        struct iio_dev *indio_dev;
        struct am2315_data *data;

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

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

        indio_dev->info = &am2315_info;
        indio_dev->name = AM2315_DRIVER_NAME;
        indio_dev->modes = INDIO_DIRECT_MODE;
        indio_dev->channels = am2315_channels;
        indio_dev->num_channels = ARRAY_SIZE(am2315_channels);

        ret = devm_iio_triggered_buffer_setup(&client->dev,
                                        indio_dev, iio_pollfunc_store_time,
                                         am2315_trigger_handler, NULL);
        if (ret < 0) {
                dev_err(&client->dev, "iio triggered buffer setup failed\n");
                return ret;
        }

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

static const struct i2c_device_id am2315_i2c_id[] = {
        { "am2315" },
        { }
};
MODULE_DEVICE_TABLE(i2c, am2315_i2c_id);

static struct i2c_driver am2315_driver = {
        .driver = {
                .name = "am2315",
        },
        .probe =        am2315_probe,
        .id_table =         am2315_i2c_id,
};

module_i2c_driver(am2315_driver);

MODULE_AUTHOR("Tiberiu Breana <tiberiu.a.breana@intel.com>");
MODULE_DESCRIPTION("Aosong AM2315 relative humidity and temperature");
MODULE_LICENSE("GPL v2");