drivers/iio/adc/max11100.c

/*
 * iio/adc/max11100.c
 * Maxim max11100 ADC Driver with IIO interface
 *
 * Copyright (C) 2016-17 Renesas Electronics Corporation
 * Copyright (C) 2016-17 Jacopo Mondi
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/delay.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/regulator/consumer.h>
#include <linux/spi/spi.h>

#include <linux/iio/iio.h>
#include <linux/iio/driver.h>

/*
 * LSB is the ADC single digital step
 * 1 LSB = (vref_mv / 2 ^ 16)
 *
 * LSB is used to calculate analog voltage value
 * from the number of ADC steps count
 *
 * Ain = (count * LSB)
 */
#define MAX11100_LSB_DIV		(1 << 16)

struct max11100_state {
	struct regulator *vref_reg;
	struct spi_device *spi;

	/*
	 * DMA (thus cache coherency maintenance) requires the
	 * transfer buffers to live in their own cache lines.
	 */
	u8 buffer[3] ____cacheline_aligned;
};

static struct iio_chan_spec max11100_channels[] = {
	{ /* [0] */
		.type = IIO_VOLTAGE,
		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW) |
				      BIT(IIO_CHAN_INFO_SCALE),
	},
};

static int max11100_read_single(struct iio_dev *indio_dev, int *val)
{
	int ret;
	struct max11100_state *state = iio_priv(indio_dev);

	ret = spi_read(state->spi, state->buffer, sizeof(state->buffer));
	if (ret) {
		dev_err(&indio_dev->dev, "SPI transfer failed\n");
		return ret;
	}

	/* the first 8 bits sent out from ADC must be 0s */
	if (state->buffer[0]) {
		dev_err(&indio_dev->dev, "Invalid value: buffer[0] != 0\n");
		return -EINVAL;
	}

	*val = (state->buffer[1] << 8) | state->buffer[2];

	return 0;
}

static int max11100_read_raw(struct iio_dev *indio_dev,
			     struct iio_chan_spec const *chan,
			     int *val, int *val2, long info)
{
	int ret, vref_uv;
	struct max11100_state *state = iio_priv(indio_dev);

	switch (info) {
	case IIO_CHAN_INFO_RAW:
		ret = max11100_read_single(indio_dev, val);
		if (ret)
			return ret;

		return IIO_VAL_INT;

	case IIO_CHAN_INFO_SCALE:
		vref_uv = regulator_get_voltage(state->vref_reg);
		if (vref_uv < 0)
			/* dummy regulator "get_voltage" returns -EINVAL */
			return -EINVAL;

		*val =  vref_uv / 1000;
		*val2 = MAX11100_LSB_DIV;
		return IIO_VAL_FRACTIONAL;
	}

	return -EINVAL;
}

static const struct iio_info max11100_info = {
	.read_raw = max11100_read_raw,
};

static int max11100_probe(struct spi_device *spi)
{
	int ret;
	struct iio_dev *indio_dev;
	struct max11100_state *state;

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

	spi_set_drvdata(spi, indio_dev);

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

	indio_dev->dev.parent = &spi->dev;
	indio_dev->dev.of_node = spi->dev.of_node;
	indio_dev->name = "max11100";
	indio_dev->info = &max11100_info;
	indio_dev->modes = INDIO_DIRECT_MODE;
	indio_dev->channels = max11100_channels;
	indio_dev->num_channels = ARRAY_SIZE(max11100_channels);

	state->vref_reg = devm_regulator_get(&spi->dev, "vref");
	if (IS_ERR(state->vref_reg))
		return PTR_ERR(state->vref_reg);

	ret = regulator_enable(state->vref_reg);
	if (ret)
		return ret;

	ret = iio_device_register(indio_dev);
	if (ret)
		goto disable_regulator;

	return 0;

disable_regulator:
	regulator_disable(state->vref_reg);

	return ret;
}

static int max11100_remove(struct spi_device *spi)
{
	struct iio_dev *indio_dev = spi_get_drvdata(spi);
	struct max11100_state *state = iio_priv(indio_dev);

	iio_device_unregister(indio_dev);
	regulator_disable(state->vref_reg);

	return 0;
}

static const struct of_device_id max11100_ids[] = {
	{.compatible = "maxim,max11100"},
	{ },
};
MODULE_DEVICE_TABLE(of, max11100_ids);

static struct spi_driver max11100_driver = {
	.driver = {
		.name	= "max11100",
		.of_match_table = of_match_ptr(max11100_ids),
	},
	.probe		= max11100_probe,
	.remove		= max11100_remove,
};

module_spi_driver(max11100_driver);

MODULE_AUTHOR("Jacopo Mondi <jacopo@jmondi.org>");
MODULE_DESCRIPTION("Maxim max11100 ADC Driver");
MODULE_LICENSE("GPL v2");