[PATCH v2 1/2] iio: temperature: Add MAX31865 RTD Support

[PATCH v2 1/2] iio: temperature: Add MAX31865 RTD Support

[Navin Sankar Velliangiri]

This patch adds support for Maxim MAX31865 RTD temperature
sensor support.

More information can be found in:
https://datasheets.maximintegrated.com/en/ds/MAX31865.pdf

Signed-off-by: Navin Sankar Velliangiri <navin@linumiz.com>

Note: Changes in v2:
	-> removed unnecessary header #include <linux/util_macros.h>
	-> implemented mutex to protect the device state
	-> Added __cacheline_aligned buffer to hold the raw temperature data
	-> implemented separate function to enable_bias() & disable_bias()
	-> call max31865_init() func when updating the filter
	-> Added ABI documentation for reference & testing
	-> dropped spi_set_drvdata()
---
 .../sysfs-bus-iio-temperature-max31865        |  25 ++
 drivers/iio/temperature/Kconfig               |  10 +
 drivers/iio/temperature/Makefile              |   1 +
 drivers/iio/temperature/max31865.c            | 347 ++++++++++++++++++
 4 files changed, 383 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
 create mode 100644 drivers/iio/temperature/max31865.c

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865 b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
new file mode 100644
index 000000000000..7ca1e09b73f5
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
@@ -0,0 +1,25 @@
+What:		/sys/bus/iio/devices/iio:deviceX/fault_ovuv
+KernelVersion:	5.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Overvoltage or Undervoltage Input fault. The internal circuitry
+		is protected from excessive voltages applied to the thermocouple
+		cables at FORCE+, FORCE2, RTDIN+ & RTDIN-. This circuitry turn
+		off when the input voltage is negative or greater than VDD.
+
+		Reading returns either '1' or '0'
+
+		=== =======================================================
+		'1' The input voltage is negative or greater than VDD.
+		'0' The input voltage is positive and less than VDD (normal
+		    state).
+		=== =======================================================
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_temp_filter_notch_frequency
+KernelVersion:	5.11
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Notch frequency in Hz for a noise rejection filter. Used i.e for
+		line noise rejection.
+
+		Valid notch filter values are 50 Hz and 60 Hz.
diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
index 4df60082c1fa..c9412abca069 100644
--- a/drivers/iio/temperature/Kconfig
+++ b/drivers/iio/temperature/Kconfig
@@ -128,4 +128,14 @@ config MAX31856
 	  This driver can also be built as a module.  If so, the module
 	  will be called max31856.
 
+config MAX31865
+	tristate "MAX31865 RTD to Digital converter"
+	depends on SPI
+	help
+	  If you say yes here you get support for MAX31865
+	  thermocouple sensor chip connected via SPI.
+
+	  This driver can also be build as a module. If so, the module
+	  will be called max31865.
+
 endmenu
diff --git a/drivers/iio/temperature/Makefile b/drivers/iio/temperature/Makefile
index 90c113115422..a8f3187258dc 100644
--- a/drivers/iio/temperature/Makefile
+++ b/drivers/iio/temperature/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_LTC2983) += ltc2983.o
 obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
 obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
 obj-$(CONFIG_MAX31856) += max31856.o
+obj-$(CONFIG_MAX31865) += max31865.o
 obj-$(CONFIG_MLX90614) += mlx90614.o
 obj-$(CONFIG_MLX90632) += mlx90632.o
 obj-$(CONFIG_TMP006) += tmp006.o
diff --git a/drivers/iio/temperature/max31865.c b/drivers/iio/temperature/max31865.c
new file mode 100644
index 000000000000..9a6ee251bb3e
--- /dev/null
+++ b/drivers/iio/temperature/max31865.c
@@ -0,0 +1,347 @@
+// 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/module.h>
+#include <linux/iio/iio.h>
+#include <linux/iio/sysfs.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 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;
+	u8 buf[2] ____cacheline_aligned;
+	bool filter_50hz;
+	bool three_wire;
+};
+
+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 = (data->buf[0] << 8 | data->buf[1]) >> 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 sprintf(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 sprintf(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_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0);
+static IIO_DEVICE_ATTR(in_temp_filter_notch_frequency, 0644,
+		    show_filter, set_filter, 0);
+
+static struct attribute *max31865_attributes[] = {
+	&iio_dev_attr_fault_ovuv.dev_attr.attr,
+	&iio_dev_attr_in_temp_filter_notch_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 (of_property_read_bool(spi->dev.of_node, "maxim,3-wire")) {
+		/* select 3 wire */
+		data->three_wire = 1;
+	} else {
+		/* select 2 or 4 wire */
+		data->three_wire = 0;
+	}
+
+	mutex_lock(&data->lock);
+	ret = max31865_init(data);
+	mutex_unlock(&data->lock);
+	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");
-- 
2.32.0

[PATCH v2 2/2] dt-bindings: iio: temperature: add MAXIM max31865 support

[Navin Sankar Velliangiri]

Add DT bindings for MAXIM max31865 RTD sensor.

Signed-off-by: Navin Sankar Velliangiri <navin@linumiz.com>

Note: Changes in v2:
	-> Changed the name RTD to Resistance Temperature Detector
	-> renamed maxim,no-of-wires to 3-wire
	-> fixed code alignment for the example
---
 .../iio/temperature/maxim,max31865.yaml       | 52 +++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml

diff --git a/Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml b/Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml
new file mode 100644
index 000000000000..13d288311cc6
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml
@@ -0,0 +1,52 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/temperature/maxim,max31865.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Maxim MAX31865 Resistance Temperature Detector.
+
+maintainers:
+  - Navin Sankar Velliangiri <navin@linumiz.com>
+
+description: |
+  https://datasheets.maximintegrated.com/en/ds/MAX31865.pdf
+
+properties:
+  compatible:
+    const: maxim,max31865
+
+  reg:
+    maxItems: 1
+
+  maxim,3-wire:
+    description:
+      Setting this property enables 3-wire config. Else
+      2-wire or 4-wire.
+    type: boolean
+
+  spi-max-frequency: true
+  spi-cpha: true
+
+required:
+  - compatible
+  - reg
+  - spi-cpha
+
+additionalProperties: false
+
+examples:
+  - |
+    spi {
+       #address-cells = <1>;
+       #size-cells = <0>;
+
+       temp_sensor@0 {
+         compatible = "maxim,max31865";
+         reg = <0>;
+         spi-max-frequency = <400000>;
+         spi-cpha;
+         maxim,3-wire;
+       };
+    };
+...
-- 
2.32.0

Re: [PATCH v2 1/2] iio: temperature: Add MAX31865 RTD Support

[Jonathan Cameron]

On Sun,  1 Aug 2021 09:13:40 +0530
Navin Sankar Velliangiri <navin@linumiz.com> wrote:

> This patch adds support for Maxim MAX31865 RTD temperature
> sensor support.
> 
> More information can be found in:
> https://datasheets.maximintegrated.com/en/ds/MAX31865.pdf
> 
> Signed-off-by: Navin Sankar Velliangiri <navin@linumiz.com>
> 

Change log goes below the --- as we don't want it to get automatically added
to the git log going fowards.  The link tag which will be added will be
fine if anyone wants to find out the history.

Otherwise, a few more comments inline.  Should be good for v3 :)

Jonathan


> Note: Changes in v2:
> 	-> removed unnecessary header #include <linux/util_macros.h>
> 	-> implemented mutex to protect the device state
> 	-> Added __cacheline_aligned buffer to hold the raw temperature data
> 	-> implemented separate function to enable_bias() & disable_bias()
> 	-> call max31865_init() func when updating the filter
> 	-> Added ABI documentation for reference & testing
> 	-> dropped spi_set_drvdata()  
> ---
>  .../sysfs-bus-iio-temperature-max31865        |  25 ++
>  drivers/iio/temperature/Kconfig               |  10 +
>  drivers/iio/temperature/Makefile              |   1 +
>  drivers/iio/temperature/max31865.c            | 347 ++++++++++++++++++
>  4 files changed, 383 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
>  create mode 100644 drivers/iio/temperature/max31865.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865 b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
> new file mode 100644
> index 000000000000..7ca1e09b73f5
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
> @@ -0,0 +1,25 @@
> +What:		/sys/bus/iio/devices/iio:deviceX/fault_ovuv
> +KernelVersion:	5.11
> +Contact:	linux-iio@vger.kernel.org
> +Description:
> +		Overvoltage or Undervoltage Input fault. The internal circuitry
> +		is protected from excessive voltages applied to the thermocouple
> +		cables at FORCE+, FORCE2, RTDIN+ & RTDIN-. This circuitry turn
> +		off when the input voltage is negative or greater than VDD.
> +
> +		Reading returns either '1' or '0'
> +
> +		=== =======================================================
> +		'1' The input voltage is negative or greater than VDD.
> +		'0' The input voltage is positive and less than VDD (normal
> +		    state).
It's a boolean so we should only need to specify one of these.

		Reading returns '1' if input voltage negative or greater than VDD,
		otherwise '0'.

Not sure the table is needed.

> +		=== =======================================================
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/in_temp_filter_notch_frequency
> +KernelVersion:	5.11
> +Contact:	linux-iio@vger.kernel.org
> +Description:
> +		Notch frequency in Hz for a noise rejection filter. Used i.e for
> +		line noise rejection.
> +
> +		Valid notch filter values are 50 Hz and 60 Hz.
> diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
> index 4df60082c1fa..c9412abca069 100644
> --- a/drivers/iio/temperature/Kconfig
> +++ b/drivers/iio/temperature/Kconfig
> @@ -128,4 +128,14 @@ config MAX31856
>  	  This driver can also be built as a module.  If so, the module
>  	  will be called max31856.
>  
> +config MAX31865
> +	tristate "MAX31865 RTD to Digital converter"
> +	depends on SPI
> +	help
> +	  If you say yes here you get support for MAX31865
> +	  thermocouple sensor chip connected via SPI.
> +
> +	  This driver can also be build as a module. If so, the module
> +	  will be called max31865.
> +
>  endmenu
> diff --git a/drivers/iio/temperature/Makefile b/drivers/iio/temperature/Makefile
> index 90c113115422..a8f3187258dc 100644
> --- a/drivers/iio/temperature/Makefile
> +++ b/drivers/iio/temperature/Makefile
> @@ -8,6 +8,7 @@ obj-$(CONFIG_LTC2983) += ltc2983.o
>  obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
>  obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
>  obj-$(CONFIG_MAX31856) += max31856.o
> +obj-$(CONFIG_MAX31865) += max31865.o
>  obj-$(CONFIG_MLX90614) += mlx90614.o
>  obj-$(CONFIG_MLX90632) += mlx90632.o
>  obj-$(CONFIG_TMP006) += tmp006.o
> diff --git a/drivers/iio/temperature/max31865.c b/drivers/iio/temperature/max31865.c
> new file mode 100644
> index 000000000000..9a6ee251bb3e
> --- /dev/null
> +++ b/drivers/iio/temperature/max31865.c
> @@ -0,0 +1,347 @@
> +// 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/module.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.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 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;
> +	u8 buf[2] ____cacheline_aligned;

Needs to be the last element.  As it stands, filter_50Hz and three_wire
are in the same cacheline.  Thus if they were to change whilst DMA was in
progress that change might 'disappear'.

> +	bool filter_50hz;
> +	bool three_wire;
> +};
> +
> +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 = (data->buf[0] << 8 | data->buf[1]) >> 1;

get_unaligned_be16(...) >> 1;
preferred as it expresses the semantics of what is going on here.

> +
> +	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 sprintf(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 sprintf(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);

If you are calling it somewhere other than init, perhaps the function needs renaming?
max31865_config() or something like that?

> +	mutex_unlock(&data->lock);
> +	if (ret)
> +		return ret;
> +
> +	return len;
> +}
> +
> +static IIO_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0);
> +static IIO_DEVICE_ATTR(in_temp_filter_notch_frequency, 0644,
> +		    show_filter, set_filter, 0);
> +
> +static struct attribute *max31865_attributes[] = {
> +	&iio_dev_attr_fault_ovuv.dev_attr.attr,
> +	&iio_dev_attr_in_temp_filter_notch_frequency.dev_attr.attr,

Notch filtering is common enough, we should consider adding this as standard
ABI supported via a new info_mask element.  We could do that as a follow up
patch though. Alternatively IIO does have the ext_info support which includes
convenient enum macros you might find simplify your implementation of this.

I'd expect to also see in_temp_filter_notch_frequency_avail here.

> +	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 (of_property_read_bool(spi->dev.of_node, "maxim,3-wire")) {
> +		/* select 3 wire */
> +		data->three_wire = 1;
> +	} else {
> +		/* select 2 or 4 wire */
> +		data->three_wire = 0;
> +	}
> +
> +	mutex_lock(&data->lock);
> +	ret = max31865_init(data);
> +	mutex_unlock(&data->lock);
> +	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");

Re: [PATCH v2 2/2] dt-bindings: iio: temperature: add MAXIM max31865 support

[Jonathan Cameron]

On Sun,  1 Aug 2021 09:13:41 +0530
Navin Sankar Velliangiri <navin@linumiz.com> wrote:

> Add DT bindings for MAXIM max31865 RTD sensor.
> 
> Signed-off-by: Navin Sankar Velliangiri <navin@linumiz.com>
> 
> Note: Changes in v2:
> 	-> Changed the name RTD to Resistance Temperature Detector
> 	-> renamed maxim,no-of-wires to 3-wire
> 	-> fixed code alignment for the example  
As in previous, move changelog below the ---
One request for more detail inline.

Thanks,

J
> ---
>  .../iio/temperature/maxim,max31865.yaml       | 52 +++++++++++++++++++
>  1 file changed, 52 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml b/Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml
> new file mode 100644
> index 000000000000..13d288311cc6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/temperature/maxim,max31865.yaml
> @@ -0,0 +1,52 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iio/temperature/maxim,max31865.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Maxim MAX31865 Resistance Temperature Detector.
> +
> +maintainers:
> +  - Navin Sankar Velliangiri <navin@linumiz.com>
> +
> +description: |
> +  https://datasheets.maximintegrated.com/en/ds/MAX31865.pdf
> +
> +properties:
> +  compatible:
> +    const: maxim,max31865
> +
> +  reg:
> +    maxItems: 1
> +
> +  maxim,3-wire:
> +    description:
> +      Setting this property enables 3-wire config. Else
> +      2-wire or 4-wire.

Oddly short wrapping on line.  Keep to 80 chars.
Please add add a little more info here about this.
Right now a reader might think this was some sort of odd spi
bus related control (particularly as there are common 3 and 4
wire versions of SPI)

> +    type: boolean
> +
> +  spi-max-frequency: true
> +  spi-cpha: true
> +
> +required:
> +  - compatible
> +  - reg
> +  - spi-cpha
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    spi {
> +       #address-cells = <1>;
> +       #size-cells = <0>;
> +
> +       temp_sensor@0 {
> +         compatible = "maxim,max31865";
> +         reg = <0>;
> +         spi-max-frequency = <400000>;
> +         spi-cpha;
> +         maxim,3-wire;
> +       };
> +    };
> +...

Re: [PATCH v2 1/2] iio: temperature: Add MAX31865 RTD Support

[Alexandru Ardelean]

On Sun, Aug 1, 2021 at 7:06 AM Navin Sankar Velliangiri
<navin@linumiz.com> wrote:
>
> This patch adds support for Maxim MAX31865 RTD temperature
> sensor support.
>
> More information can be found in:
> https://datasheets.maximintegrated.com/en/ds/MAX31865.pdf
>
> Signed-off-by: Navin Sankar Velliangiri <navin@linumiz.com>
>
> Note: Changes in v2:
>         -> removed unnecessary header #include <linux/util_macros.h>
>         -> implemented mutex to protect the device state
>         -> Added __cacheline_aligned buffer to hold the raw temperature data
>         -> implemented separate function to enable_bias() & disable_bias()
>         -> call max31865_init() func when updating the filter
>         -> Added ABI documentation for reference & testing
>         -> dropped spi_set_drvdata()
> ---
>  .../sysfs-bus-iio-temperature-max31865        |  25 ++
>  drivers/iio/temperature/Kconfig               |  10 +
>  drivers/iio/temperature/Makefile              |   1 +
>  drivers/iio/temperature/max31865.c            | 347 ++++++++++++++++++
>  4 files changed, 383 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
>  create mode 100644 drivers/iio/temperature/max31865.c
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865 b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
> new file mode 100644
> index 000000000000..7ca1e09b73f5
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31865
> @@ -0,0 +1,25 @@
> +What:          /sys/bus/iio/devices/iio:deviceX/fault_ovuv
> +KernelVersion: 5.11
> +Contact:       linux-iio@vger.kernel.org
> +Description:
> +               Overvoltage or Undervoltage Input fault. The internal circuitry
> +               is protected from excessive voltages applied to the thermocouple
> +               cables at FORCE+, FORCE2, RTDIN+ & RTDIN-. This circuitry turn
> +               off when the input voltage is negative or greater than VDD.
> +
> +               Reading returns either '1' or '0'
> +
> +               === =======================================================
> +               '1' The input voltage is negative or greater than VDD.
> +               '0' The input voltage is positive and less than VDD (normal
> +                   state).
> +               === =======================================================
> +
> +What:          /sys/bus/iio/devices/iio:deviceX/in_temp_filter_notch_frequency
> +KernelVersion: 5.11
> +Contact:       linux-iio@vger.kernel.org
> +Description:
> +               Notch frequency in Hz for a noise rejection filter. Used i.e for
> +               line noise rejection.
> +
> +               Valid notch filter values are 50 Hz and 60 Hz.
> diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
> index 4df60082c1fa..c9412abca069 100644
> --- a/drivers/iio/temperature/Kconfig
> +++ b/drivers/iio/temperature/Kconfig
> @@ -128,4 +128,14 @@ config MAX31856
>           This driver can also be built as a module.  If so, the module
>           will be called max31856.
>
> +config MAX31865
> +       tristate "MAX31865 RTD to Digital converter"
> +       depends on SPI
> +       help
> +         If you say yes here you get support for MAX31865
> +         thermocouple sensor chip connected via SPI.
> +
> +         This driver can also be build as a module. If so, the module
> +         will be called max31865.
> +
>  endmenu
> diff --git a/drivers/iio/temperature/Makefile b/drivers/iio/temperature/Makefile
> index 90c113115422..a8f3187258dc 100644
> --- a/drivers/iio/temperature/Makefile
> +++ b/drivers/iio/temperature/Makefile
> @@ -8,6 +8,7 @@ obj-$(CONFIG_LTC2983) += ltc2983.o
>  obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
>  obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
>  obj-$(CONFIG_MAX31856) += max31856.o
> +obj-$(CONFIG_MAX31865) += max31865.o
>  obj-$(CONFIG_MLX90614) += mlx90614.o
>  obj-$(CONFIG_MLX90632) += mlx90632.o
>  obj-$(CONFIG_TMP006) += tmp006.o
> diff --git a/drivers/iio/temperature/max31865.c b/drivers/iio/temperature/max31865.c
> new file mode 100644
> index 000000000000..9a6ee251bb3e
> --- /dev/null
> +++ b/drivers/iio/temperature/max31865.c
> @@ -0,0 +1,347 @@
> +// 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/module.h>
> +#include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.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 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;
> +       u8 buf[2] ____cacheline_aligned;
> +       bool filter_50hz;
> +       bool three_wire;
> +};
> +
> +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 = (data->buf[0] << 8 | data->buf[1]) >> 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 sprintf(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 sprintf(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_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0);
> +static IIO_DEVICE_ATTR(in_temp_filter_notch_frequency, 0644,
> +                   show_filter, set_filter, 0);
> +
> +static struct attribute *max31865_attributes[] = {
> +       &iio_dev_attr_fault_ovuv.dev_attr.attr,
> +       &iio_dev_attr_in_temp_filter_notch_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 (of_property_read_bool(spi->dev.of_node, "maxim,3-wire")) {
> +               /* select 3 wire */
> +               data->three_wire = 1;
> +       } else {
> +               /* select 2 or 4 wire */
> +               data->three_wire = 0;
> +       }
> +
> +       mutex_lock(&data->lock);
> +       ret = max31865_init(data);
> +       mutex_unlock(&data->lock);

There aren't any changes for race-conditions here.
There is no userspace access to the device yet (before
devm_iio_device_register() is being called).
So, the locking can be removed [here] in probe().

> +       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");
> --
> 2.32.0
>