drivers/iio/temperature/max31865.c

// SPDX-License-Identifier: GPL-2.0-only

/*
 * Copyright (c) Linumiz 2021
 *
 * max31865.c - Maxim MAX31865 RTD-to-Digital Converter sensor driver
 *
 * Author: Navin Sankar Velliangiri <navin@linumiz.com>
 */

#include <linux/ctype.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/init.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/iio/iio.h>
#include <linux/iio/sysfs.h>
#include <linux/property.h>
#include <linux/spi/spi.h>
#include <asm/unaligned.h>

/*
 * The MSB of the register value determines whether the following byte will
 * be written or read. If it is 0, read will follow and if it is 1, write
 * will follow.
 */
#define MAX31865_RD_WR_BIT			BIT(7)

#define MAX31865_CFG_VBIAS			BIT(7)
#define MAX31865_CFG_1SHOT			BIT(5)
#define MAX31865_3WIRE_RTD			BIT(4)
#define MAX31865_FAULT_STATUS_CLEAR		BIT(1)
#define MAX31865_FILTER_50HZ			BIT(0)

/* The MAX31865 registers */
#define MAX31865_CFG_REG			0x00
#define MAX31865_RTD_MSB			0x01
#define MAX31865_FAULT_STATUS			0x07

#define MAX31865_FAULT_OVUV			BIT(2)

static const char max31865_show_samp_freq[] = "50 60";

static const struct iio_chan_spec max31865_channels[] = {
	{	/* RTD Temperature */
		.type = IIO_TEMP,
		.info_mask_separate =
			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE)
	},
};

struct max31865_data {
	struct spi_device *spi;
	struct mutex lock;
	bool filter_50hz;
	bool three_wire;
	u8 buf[2] __aligned(IIO_DMA_MINALIGN);
};

static int max31865_read(struct max31865_data *data, u8 reg,
			 unsigned int read_size)
{
	return spi_write_then_read(data->spi, &reg, 1, data->buf, read_size);
}

static int max31865_write(struct max31865_data *data, size_t len)
{
	return spi_write(data->spi, data->buf, len);
}

static int enable_bias(struct max31865_data *data)
{
	u8 cfg;
	int ret;

	ret = max31865_read(data, MAX31865_CFG_REG, 1);
	if (ret)
		return ret;

	cfg = data->buf[0];

	data->buf[0] = MAX31865_CFG_REG | MAX31865_RD_WR_BIT;
	data->buf[1] = cfg | MAX31865_CFG_VBIAS;

	return max31865_write(data, 2);
}

static int disable_bias(struct max31865_data *data)
{
	u8 cfg;
	int ret;

	ret = max31865_read(data, MAX31865_CFG_REG, 1);
	if (ret)
		return ret;

	cfg = data->buf[0];
	cfg &= ~MAX31865_CFG_VBIAS;

	data->buf[0] = MAX31865_CFG_REG | MAX31865_RD_WR_BIT;
	data->buf[1] = cfg;

	return max31865_write(data, 2);
}

static int max31865_rtd_read(struct max31865_data *data, int *val)
{
	u8 reg;
	int ret;

	/* Enable BIAS to start the conversion */
	ret = enable_bias(data);
	if (ret)
		return ret;

	/* wait 10.5ms before initiating the conversion */
	msleep(11);

	ret = max31865_read(data, MAX31865_CFG_REG, 1);
	if (ret)
		return ret;

	reg = data->buf[0];
	reg |= MAX31865_CFG_1SHOT | MAX31865_FAULT_STATUS_CLEAR;
	data->buf[0] = MAX31865_CFG_REG | MAX31865_RD_WR_BIT;
	data->buf[1] = reg;

	ret = max31865_write(data, 2);
	if (ret)
		return ret;

	if (data->filter_50hz) {
		/* 50Hz filter mode requires 62.5ms to complete */
		msleep(63);
	} else {
		/* 60Hz filter mode requires 52ms to complete */
		msleep(52);
	}

	ret = max31865_read(data, MAX31865_RTD_MSB, 2);
	if (ret)
		return ret;

	*val = get_unaligned_be16(&data->buf) >> 1;

	return disable_bias(data);
}

static int max31865_read_raw(struct iio_dev *indio_dev,
			     struct iio_chan_spec const *chan,
			     int *val, int *val2, long mask)
{
	struct max31865_data *data = iio_priv(indio_dev);
	int ret;

	switch (mask) {
	case IIO_CHAN_INFO_RAW:
		mutex_lock(&data->lock);
		ret = max31865_rtd_read(data, val);
		mutex_unlock(&data->lock);
		if (ret)
			return ret;
		return IIO_VAL_INT;
	case IIO_CHAN_INFO_SCALE:
		/* Temp. Data resolution is 0.03125 degree centigrade */
		*val = 31;
		*val2 = 250000; /* 1000 * 0.03125 */
		return IIO_VAL_INT_PLUS_MICRO;
	default:
		return -EINVAL;
	}
}

static int max31865_init(struct max31865_data *data)
{
	u8 cfg;
	int ret;

	ret = max31865_read(data, MAX31865_CFG_REG, 1);
	if (ret)
		return ret;

	cfg = data->buf[0];

	if (data->three_wire)
		/* 3-wire RTD connection */
		cfg |= MAX31865_3WIRE_RTD;

	if (data->filter_50hz)
		/* 50Hz noise rejection filter */
		cfg |= MAX31865_FILTER_50HZ;

	data->buf[0] = MAX31865_CFG_REG | MAX31865_RD_WR_BIT;
	data->buf[1] = cfg;

	return max31865_write(data, 2);
}

static ssize_t show_fault(struct device *dev, u8 faultbit, char *buf)
{
	int ret;
	bool fault;
	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
	struct max31865_data *data = iio_priv(indio_dev);

	ret = max31865_read(data, MAX31865_FAULT_STATUS, 1);
	if (ret)
		return ret;

	fault = data->buf[0] & faultbit;

	return sysfs_emit(buf, "%d\n", fault);
}

static ssize_t show_fault_ovuv(struct device *dev,
			      struct device_attribute *attr,
			      char *buf)
{
	return show_fault(dev, MAX31865_FAULT_OVUV, buf);
}

static ssize_t show_filter(struct device *dev,
			   struct device_attribute *attr,
			   char *buf)
{
	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
	struct max31865_data *data = iio_priv(indio_dev);

	return sysfs_emit(buf, "%d\n", data->filter_50hz ? 50 : 60);
}

static ssize_t set_filter(struct device *dev,
			  struct device_attribute *attr,
			  const char *buf,
			  size_t len)
{
	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
	struct max31865_data *data = iio_priv(indio_dev);
	unsigned int freq;
	int ret;

	ret = kstrtouint(buf, 10, &freq);
	if (ret)
		return ret;

	switch (freq) {
	case 50:
		data->filter_50hz = true;
		break;
	case 60:
		data->filter_50hz = false;
		break;
	default:
		return -EINVAL;
	}

	mutex_lock(&data->lock);
	ret = max31865_init(data);
	mutex_unlock(&data->lock);
	if (ret)
		return ret;

	return len;
}

static IIO_CONST_ATTR_SAMP_FREQ_AVAIL(max31865_show_samp_freq);
static IIO_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0);
static IIO_DEVICE_ATTR(in_filter_notch_center_frequency, 0644,
		    show_filter, set_filter, 0);

static struct attribute *max31865_attributes[] = {
	&iio_dev_attr_fault_ovuv.dev_attr.attr,
	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
	&iio_dev_attr_in_filter_notch_center_frequency.dev_attr.attr,
	NULL,
};

static const struct attribute_group max31865_group = {
	.attrs = max31865_attributes,
};

static const struct iio_info max31865_info = {
	.read_raw = max31865_read_raw,
	.attrs = &max31865_group,
};

static int max31865_probe(struct spi_device *spi)
{
	const struct spi_device_id *id = spi_get_device_id(spi);
	struct iio_dev *indio_dev;
	struct max31865_data *data;
	int ret;

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

	data = iio_priv(indio_dev);
	data->spi = spi;
	data->filter_50hz = false;
	mutex_init(&data->lock);

	indio_dev->info = &max31865_info;
	indio_dev->name = id->name;
	indio_dev->modes = INDIO_DIRECT_MODE;
	indio_dev->channels = max31865_channels;
	indio_dev->num_channels = ARRAY_SIZE(max31865_channels);

	if (device_property_read_bool(&spi->dev, "maxim,3-wire")) {
		/* select 3 wire */
		data->three_wire = 1;
	} else {
		/* select 2 or 4 wire */
		data->three_wire = 0;
	}

	ret = max31865_init(data);
	if (ret) {
		dev_err(&spi->dev, "error: Failed to configure max31865\n");
		return ret;
	}

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

static const struct spi_device_id max31865_id[] = {
	{ "max31865", 0 },
	{ }
};
MODULE_DEVICE_TABLE(spi, max31865_id);

static const struct of_device_id max31865_of_match[] = {
	{ .compatible = "maxim,max31865" },
	{ }
};
MODULE_DEVICE_TABLE(of, max31865_of_match);

static struct spi_driver max31865_driver = {
	.driver = {
		.name	= "max31865",
		.of_match_table = max31865_of_match,
	},
	.probe = max31865_probe,
	.id_table = max31865_id,
};
module_spi_driver(max31865_driver);

MODULE_AUTHOR("Navin Sankar Velliangiri <navin@linumiz.com>");
MODULE_DESCRIPTION("Maxim MAX31865 RTD-to-Digital Converter sensor driver");
MODULE_LICENSE("GPL v2");