Re: [PATCH 1/2] iio:temperature: Add MAX31856 thermocouple support

[Peter Meerwald-Stadler <pmeerw@pmeerw.net>]

> From: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
> 
> This patch adds support for Maxim MAX31856 thermocouple
> temperature sensor support.

some comments below

> More information can be found in:
> https://www.maximintegrated.com/en/ds/MAX31856.pdf
> 
> NOTE: Driver support only Comparator Mode.
> 
> Signed-off-by: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
> Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
> ---
> 
> We assumed this should be applied and patch checked against the iio testing
> branch found in the staging repo.
> (git://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git)
> 
> ---
> 
>  MAINTAINERS                        |   5 +
>  drivers/iio/temperature/Kconfig    |  10 +
>  drivers/iio/temperature/Makefile   |   1 +
>  drivers/iio/temperature/max31856.c | 374 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 390 insertions(+)
>  create mode 100644 drivers/iio/temperature/max31856.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index f642044..dd9a83d 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -7157,6 +7157,11 @@ F:	drivers/staging/iio/
>  F:	include/linux/iio/
>  F:	tools/iio/
>  
> +MAX31856 IIO DRIVER
> +M:	Matthew Weber <matthew.weber@rockwellcollins.com>
> +S:	Maintained
> +F:	drivers/iio/temperature/max31856.c
> +
>  IIO UNIT CONVERTER
>  M:	Peter Rosin <peda@axentia.se>
>  L:	linux-iio@vger.kernel.org
> diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
> index 82e4a62..c66eeb2 100644
> --- a/drivers/iio/temperature/Kconfig
> +++ b/drivers/iio/temperature/Kconfig
> @@ -97,4 +97,14 @@ config TSYS02D
>  	  This driver can also be built as a module. If so, the module will
>  	  be called tsys02d.
>  
> +config MAX31856
> +	tristate "MAX31856 thermocouple sensor"
> +	depends on SPI
> +	help
> +	  If you say yes here you get support for MAX31856
> +	  thermocouple sensor chip connected via SPI.
> +
> +	  This driver can also be built as a module.  If so, the module
> +	  will be called max31856.
> +
>  endmenu
> diff --git a/drivers/iio/temperature/Makefile b/drivers/iio/temperature/Makefile
> index 34a31db..38cf178 100644
> --- a/drivers/iio/temperature/Makefile
> +++ b/drivers/iio/temperature/Makefile
> @@ -11,3 +11,4 @@ obj-$(CONFIG_TMP006) += tmp006.o
>  obj-$(CONFIG_TMP007) += tmp007.o
>  obj-$(CONFIG_TSYS01) += tsys01.o
>  obj-$(CONFIG_TSYS02D) += tsys02d.o
> +obj-$(CONFIG_MAX31856) += max31856.o

alphabethic order please

> diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
> new file mode 100644
> index 0000000..eb5a03c
> --- /dev/null
> +++ b/drivers/iio/temperature/max31856.c
> @@ -0,0 +1,374 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* max31856.c
> + *
> + * Maxim MAX31856 thermocouple sensor driver
> + *
> + * Copyright (C) 2018 Rockwell Collins
> + *

license text can be skipped thanks to SPDX line

> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/err.h>
> +#include <linux/spi/spi.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
> +
> +#define MAX31856_READ_MODE	   0x7F
> +#define MAX31856_WRITE_MODE	   0x80
> +
> +/* The MAX31856 registers */
> +#define MAX31856_CR0_REG           0x00
> +#define MAX31856_CR1_REG           0x01
> +#define MAX31856_MASK_REG          0x02
> +#define MAX31856_CJHF_REG          0x03
> +#define MAX31856_CJLF_REG          0x04
> +#define MAX31856_LTHFTH_REG        0x05
> +#define MAX31856_LTHFTL_REG        0x06
> +#define MAX31856_LTLFTH_REG        0x07
> +#define MAX31856_LTLFTL_REG        0x08
> +#define MAX31856_CJTO_REG          0x09
> +#define MAX31856_CJTH_REG          0x0A
> +#define MAX31856_CJTL_REG          0x0B
> +#define MAX31856_LTCBH_REG         0x0C
> +#define MAX31856_LTCBM_REG         0x0D
> +#define MAX31856_LTCBL_REG         0x0E
> +#define MAX31856_SR_REG            0x0F
> +
> +static const struct iio_chan_spec max31856_channels[] = {
> +	{	/* Thermocouple Temperature */
> +		.type = IIO_TEMP,
> +		.address = 2,
> +		.info_mask_separate =
> +			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +	},
> +	{	/* Cold Junction Temperature */
> +		.type = IIO_TEMP,
> +		.channel2 = IIO_MOD_TEMP_AMBIENT,
> +		.address = 0,
> +		.modified = 1,
> +		.info_mask_separate =
> +			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +	},
> +};
> +
> +struct max31856_data {
> +	struct spi_device *spi;
> +	bool one_shot;
> +	u32 thermocouple_type;
> +	int fault_ovuv;
> +	int fault_oc;
> +	u8 buf[3] ____cacheline_aligned;
> +};
> +
> +static int max31856_read(struct max31856_data *data, unsigned int reg,
> +			 s32 *val, int read_size)
> +{
> +	int ret = 0;

no need to initialize ret, will be overwritten anyways

> +	u8 *buf = data->buf;
> +
> +	/* Make sure top bit is not set,
> +	 * The MSB(A7) of this byte determines whether the following byte will
> +	 * be written or read If A7 is 0, one or more byte reads will follow the

maybe use a full stop (.) after read / before If for readability

> +	 * address byte
> +	 */
> +
> +	reg &= MAX31856_READ_MODE;
> +
> +	buf[0] = reg;
> +	buf[1] = 0x00;
> +	buf[2] = 0x00;
> +
> +	ret = spi_write_then_read(data->spi, buf, 1, buf, read_size);
> +	if (ret < 0)
> +		return ret;
> +
> +	switch (read_size) {
> +	case 1:
> +		*val = buf[0];
> +		break;

just return directly:
return 0;

> +	case 2:
> +		*val = (buf[0] << 8) | buf[1];
> +		break;
> +	case 3:
> +		*val = (buf[0] << 16) | (buf[1] << 8) | buf[2];
> +		break;
> +	default:
> +		ret = -1;

return -EINVAL
shouldn't the read_size be checked before to avoid overflowing buf?

> +	}
> +
> +	return ret;
> +}
> +
> +static int max31856_write(struct max31856_data *data, unsigned int reg,
> +			  unsigned int val)
> +{
> +	u8 *buf = data->buf;
> +
> +	/* Make sure top bit is set,
> +	 * The MSB(A7) of this byte determines whether the following byte will
> +	 * be written or read If A7 is 1, one or more byte writes will follow

. before If

> +	 * the address byte
> +	 */
> +
> +	reg |= MAX31856_WRITE_MODE;
> +
> +	buf[0] = reg;
> +	buf[1] = val;
> +
> +	return spi_write(data->spi, buf, 2);
> +}
> +
> +static int max31856_init(struct max31856_data *data)
> +{
> +	int ret = 0;
> +	s32 reg_val;
> +
> +	/* Enable Open circuit fault detection [01]
> +	 * Read datasheet for more information: Table 4.
> +	 * BITS [5:4]    | Fault Test
> +	 * ---------------------------
> +	 *	00    | Disabled
> +	 * ---------------------------
> +	 *	01    | Enabled(Once every 16 seconds)

maybe a space after Enabled?
> +	 * ---------------------------
> +	 *	10    | Enabled(Once every 16 seconds)
> +	 * ---------------------------
> +	 *	11    | Enabled(Once every 16 seconds)
> +	 */
> +	ret = max31856_read(data, MAX31856_CR0_REG, &reg_val, 1);
> +	if (ret)
> +		return ret;
> +	reg_val &= ~BIT(5);

use #defines for these magic bits and masks in here

> +	reg_val |= BIT(4);
> +	ret = max31856_write(data, MAX31856_CR0_REG, reg_val);
> +	if (ret)
> +		return ret;
> +
> +	/* Set thermocouple type based on dts property */
> +	ret = max31856_read(data, MAX31856_CR1_REG, &reg_val, 1);
> +	if (ret)
> +		return ret;
> +
> +	reg_val &= 0x00F0;
> +	reg_val |= (data->thermocouple_type & 0x0F);
> +	ret = max31856_write(data, MAX31856_CR1_REG, reg_val);
> +	if (ret)
> +		return ret;
> +
> +	/* Set Conversion Mode (Auto or Oneshot) based on dts property */
> +	ret = max31856_read(data, MAX31856_CR0_REG, &reg_val, 1);
> +	if (ret)
> +		return ret;
> +	if (data->one_shot) {
> +		reg_val &= ~BIT(7);
> +		reg_val |= BIT(6);
> +	} else {
> +		reg_val |= BIT(7);
> +		reg_val &= ~BIT(6);
> +	}
> +	ret = max31856_write(data, MAX31856_CR0_REG, reg_val);

just 
return max31856_write(...);

> +
> +	return ret;
> +}
> +
> +static int max31856_thermocouple_read(struct max31856_data *data,
> +				      struct iio_chan_spec const *chan,
> +				      int *val)
> +{
> +	int ret = 0, temp, offset_cjto;
> +
> +	switch (chan->channel2) {
> +	case IIO_MOD_TEMP_AMBIENT:
> +		/* Read register from 0x09-0x0B */
> +		ret = max31856_read(data, MAX31856_CJTO_REG, val, 3);
> +		/* Get Cold Junction Temp. offset register value */
> +		offset_cjto = *val >> 16;
> +		/* Mask last 2 bytes to get CJTH and CJTL reg. value */
> +		*val &= 0x0000FFFF;
> +		temp = *val;
> +		/* last 2 bits unused in CJTL reg*/
> +		*val >>= 2;
> +		/* As per datasheet add offset into CJTH and CJTL */
> +		*val += offset_cjto;
> +		/* Check 15th bit for sign */
> +		if (temp & 0x8000)
> +			*val -= 0x4000;
> +		break;
> +	default:
> +		ret = max31856_read(data, MAX31856_LTCBH_REG, val, 3);
> +		temp = *val;
> +		*val >>= 5;
> +		/* Check 23th bit for sign */
> +		if (temp & 0x800000)
> +			*val -= 0x80000;
> +	}
> +
> +	ret = max31856_read(data, MAX31856_SR_REG, &temp, 1);
> +	/*Check for over voltage/under voltage fault */

space before Check

> +	data->fault_ovuv = (temp & BIT(1)) ? 1 : 0;
> +	/* Check for open circuit fault */
> +	data->fault_oc = (temp & BIT(0)) ? 1 : 0;

what to do with these error conditions, maybe return -EIO?

> +
> +	return ret;
> +}
> +
> +static int max31856_read_raw(struct iio_dev *indio_dev,
> +			     struct iio_chan_spec const *chan,
> +			     int *val, int *val2, long mask)
> +{
> +	struct max31856_data *data = iio_priv(indio_dev);
> +	int ret = -EINVAL;

no need to initialize ret

> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		ret = max31856_thermocouple_read(data, chan, val);
> +		if (ret)
> +			return ret;
> +		else
> +			return IIO_VAL_INT;
> +		break;

why not just.
	ret = max31856_thermocouple_read(data, chan, val);
	if (ret)
		return ret;
	return IIO_VAL_INT;

> +	case IIO_CHAN_INFO_SCALE:
> +		switch (chan->channel2) {
> +		case IIO_MOD_TEMP_AMBIENT:
> +			/* Cold junction Temp. Data resolution is 0.015625 */
> +			*val = 15;
> +			*val2 = 625000; /* 1000 * 0.015625 */
> +			ret = IIO_VAL_INT_PLUS_MICRO;
> +			break;
> +		default:
> +			/* Thermocouple Temp. Data resolution is 0.0078125 */
> +			*val = 7;
> +			*val2 = 812500; /* 1000 * 0.0078125) */
> +			ret = IIO_VAL_INT_PLUS_MICRO;

just
return IIO_VAL_INT_PLUS_MICRO;

> +		};

no semicolon after }

> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static const struct iio_info max31856_info = {
> +	.driver_module = THIS_MODULE,
> +	.read_raw = max31856_read_raw,
> +};
> +
> +static ssize_t show_fault_ovuv(struct device *dev,
> +			       struct device_attribute *attr,
> +			       char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct max31856_data *data = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%d\n", data->fault_ovuv);
> +}
> +
> +static ssize_t show_fault_oc(struct device *dev,
> +			     struct device_attribute *attr,
> +			     char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct max31856_data *data = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%d\n", data->fault_oc);
> +}
> +
> +static IIO_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0);
> +static IIO_DEVICE_ATTR(fault_oc, 0444, show_fault_oc, NULL, 0);
> +
> +static struct attribute *max31856_attributes[] = {
> +	&iio_dev_attr_fault_ovuv.dev_attr.attr,
> +	&iio_dev_attr_fault_oc.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group max31856_group = {
> +	.attrs = max31856_attributes,
> +};
> +
> +static int max31856_probe(struct spi_device *spi)
> +{
> +	const struct spi_device_id *id = spi_get_device_id(spi);
> +	struct iio_dev *indio_dev;
> +	struct max31856_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;
> +
> +	spi_set_drvdata(spi, indio_dev);
> +
> +	indio_dev->info = &max31856_info;
> +	indio_dev->name = id->name;
> +	indio_dev->modes = INDIO_DIRECT_MODE;
> +	indio_dev->channels = max31856_channels;
> +	indio_dev->num_channels = ARRAY_SIZE(max31856_channels);
> +
> +	data->one_shot = of_property_read_bool(spi->dev.of_node, "one-shot");
> +
> +	ret = of_property_read_u32(spi->dev.of_node, "type",
> +				   &data->thermocouple_type);
> +
> +	if (ret) {
> +		pr_info("Could not read thermocouple type DT property, Configuring as a K-Type\n");
> +		data->thermocouple_type = 0x03; /* K-Type */
> +	}
> +
> +	ret = max31856_init(data);
> +	if (ret) {
> +		pr_err("error: Failed to configure max31856\n");
> +		return ret;
> +	}
> +
> +	ret = iio_device_register(indio_dev);
> +
> +	data->fault_ovuv = 0;
> +	data->fault_oc = 0;

not needed to initialize; why after _register(), racy?

> +	ret = sysfs_create_group(&indio_dev->dev.kobj, &max31856_group);

should not be needed and overwrites ret of _register()
> +
> +	return ret;
> +}
> +
> +static int max31856_remove(struct spi_device *spi)
> +{
> +	struct iio_dev *indio_dev = spi_get_drvdata(spi);
> +
> +	sysfs_remove_group(&indio_dev->dev.kobj, &max31856_group);
> +	iio_device_unregister(indio_dev);
> +
> +	return 0;
> +}
> +
> +static const struct spi_device_id max31856_id[] = {
> +	{ "max31856", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(spi, max31856_id);
> +
> +static struct spi_driver max31856_driver = {
> +	.driver = {
> +		.name = "max31856",
> +		.owner = THIS_MODULE,
> +	},
> +	.probe = max31856_probe,
> +	.remove = max31856_remove,
> +	.id_table = max31856_id,
> +};
> +module_spi_driver(max31856_driver);
> +
> +MODULE_AUTHOR("Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>");
> +MODULE_DESCRIPTION("Maxim MAX31856 thermocouple sensor driver");
> +MODULE_LICENSE("GPL");
> 

-- 

Peter Meerwald-Stadler
Mobile: +43 664 24 44 418