/**
 * Aosong AM2315 relative humidity and temperature
 *
 * Copyright (c) 2016, Intel Corporation.
 *
 * This file is subject to the terms and conditions of version 2 of
 * the GNU General Public License. See the file COPYING in the main
 * directory of this archive for more details.
 *
 * 7-bit I2C address: 0x5C.
 */

#include <linux/acpi.h>
#include <linux/delay.h>
#include <linux/i2c.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/iio/iio.h>
#include <linux/iio/sysfs.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_DRIVER_NAME			"am2315"

struct am2315_data {
	struct i2c_client *client;
	struct mutex lock;
};

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)
	},
	{
		.type = IIO_TEMP,
		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
				      BIT(IIO_CHAN_INFO_SCALE)
	},
};

/* 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 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 = {
	.driver_module		= THIS_MODULE,
	.read_raw		= am2315_read_raw,
};

static int am2315_probe(struct i2c_client *client,
			const struct i2c_device_id *id)
{
	struct iio_dev *indio_dev;
	struct am2315_data *data;

	indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data));
	if (!indio_dev) {
		dev_err(&client->dev, "iio allocation failed!\n");
		return -ENOMEM;
	}

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

	indio_dev->dev.parent = &client->dev;
	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);

	return iio_device_register(indio_dev);
}

static int am2315_remove(struct i2c_client *client)
{
	struct iio_dev *indio_dev = i2c_get_clientdata(client);

	iio_device_unregister(indio_dev);

	return 0;
}

static const struct i2c_device_id am2315_i2c_id[] = {
	{"am2315", 0},
	{}
};

static const struct acpi_device_id am2315_acpi_id[] = {
	{"AOS2315", 0},
	{}
};

MODULE_DEVICE_TABLE(acpi, am2315_acpi_id);

static struct i2c_driver am2315_driver = {
	.driver = {
		.name = "am2315",
		.acpi_match_table = ACPI_PTR(am2315_acpi_id),
	},
	.probe =            am2315_probe,
	.remove =	    am2315_remove,
	.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");