[PATCH v7 1/3] dt-bindings: iio/temperature: Add thermocouple types (and doc)

[PATCH v7 1/3] dt-bindings: iio/temperature: Add thermocouple types (and doc)

[Patrick Havelange]

This patch introduces common thermocouple types used by various
temperature sensors. Also a brief documentation explaining this
"thermocouple-type" property.

Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
---
Changes v7
 - Merge header and doc in same patch
 - Doc:add it's a single cell entry
 - Doc:removed non complete example

Changes v6
 - Add this file
---
 .../iio/temperature/temperature-bindings.txt     |  7 +++++++
 .../dt-bindings/iio/temperature/thermocouple.h   | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt
 create mode 100644 include/dt-bindings/iio/temperature/thermocouple.h

diff --git a/Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt b/Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt
new file mode 100644
index 000000000000..8f339cab74ae
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt
@@ -0,0 +1,7 @@
+If the temperature sensor device can be configured to use some specific
+thermocouple type, you can use the defined types provided in the file
+"include/dt-bindings/iio/temperature/thermocouple.h".
+
+Property:
+thermocouple-type:	A single cell representing the type of the thermocouple
+			used by the device.
diff --git a/include/dt-bindings/iio/temperature/thermocouple.h b/include/dt-bindings/iio/temperature/thermocouple.h
new file mode 100644
index 000000000000..ce037f5238ac
--- /dev/null
+++ b/include/dt-bindings/iio/temperature/thermocouple.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _DT_BINDINGS_TEMPERATURE_THERMOCOUPLE_H
+#define _DT_BINDINGS_TEMPERATURE_THERMOCOUPLE_H
+
+
+#define THERMOCOUPLE_TYPE_B	0x00
+#define THERMOCOUPLE_TYPE_E	0x01
+#define THERMOCOUPLE_TYPE_J	0x02
+#define THERMOCOUPLE_TYPE_K	0x03
+#define THERMOCOUPLE_TYPE_N	0x04
+#define THERMOCOUPLE_TYPE_R	0x05
+#define THERMOCOUPLE_TYPE_S	0x06
+#define THERMOCOUPLE_TYPE_T	0x07
+
+#endif /* _DT_BINDINGS_TEMPERATURE_THERMOCOUPLE_H */
-- 
2.19.1

[PATCH v7 2/3] iio:temperature:max31856:Add device tree bind info

[Patrick Havelange]

From: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>

This patch added device tree binding info for MAX31856 driver.

Signed-off-by: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
Reviewed-by: Rob Herring <robh@kernel.org>
---
Changes
v1 -> v2
[Matt
 - Removed comment block and added possibilities of
   thermocouple type in device tree binding doc.

v2 -> v3
 - Rebased

v3 -> v4
 - Removed one-shot property related information.
 - Used standard name 'temp-sensor'

v4 -> v5
[Patrick
 - Rename thermocouple type to maxim,thermocouple-type for DT entry

v5 -> v6
[Patrick
 - use generic thermocouple-type for DT entry

v6 -> v7
[Patrick
 - None
---
 .../bindings/iio/temperature/max31856.txt     | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/iio/temperature/max31856.txt

diff --git a/Documentation/devicetree/bindings/iio/temperature/max31856.txt b/Documentation/devicetree/bindings/iio/temperature/max31856.txt
new file mode 100644
index 000000000000..06ab43bb4de8
--- /dev/null
+++ b/Documentation/devicetree/bindings/iio/temperature/max31856.txt
@@ -0,0 +1,24 @@
+Maxim MAX31856 thermocouple support
+
+https://datasheets.maximintegrated.com/en/ds/MAX31856.pdf
+
+Optional property:
+	- thermocouple-type: Type of thermocouple (THERMOCOUPLE_TYPE_K if
+		omitted). Supported types are B, E, J, K, N, R, S, T.
+
+Required properties:
+	- compatible: must be "maxim,max31856"
+	- reg: SPI chip select number for the device
+	- spi-max-frequency: As per datasheet max. supported freq is 5000000
+	- spi-cpha: must be defined for max31856 to enable SPI mode 1
+
+	Refer to spi/spi-bus.txt for generic SPI slave bindings.
+
+ Example:
+	temp-sensor@0 {
+		compatible = "maxim,max31856";
+		reg = <0>;
+		spi-max-frequency = <5000000>;
+		spi-cpha;
+		thermocouple-type = <THERMOCOUPLE_TYPE_K>;
+	};
-- 
2.19.1

Re: [PATCH v7 2/3] iio:temperature:max31856:Add device tree bind info

[Jonathan Cameron]

On Tue, 26 Mar 2019 12:18:41 +0100
Patrick Havelange <patrick.havelange@essensium.com> wrote:

> From: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
> 
> This patch added device tree binding info for MAX31856 driver.
> 
> Signed-off-by: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
> Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
> Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
> Reviewed-by: Rob Herring <robh@kernel.org>
Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
> Changes
> v1 -> v2
> [Matt
>  - Removed comment block and added possibilities of
>    thermocouple type in device tree binding doc.
> 
> v2 -> v3
>  - Rebased
> 
> v3 -> v4
>  - Removed one-shot property related information.
>  - Used standard name 'temp-sensor'
> 
> v4 -> v5
> [Patrick
>  - Rename thermocouple type to maxim,thermocouple-type for DT entry
> 
> v5 -> v6
> [Patrick
>  - use generic thermocouple-type for DT entry
> 
> v6 -> v7
> [Patrick
>  - None
> ---
>  .../bindings/iio/temperature/max31856.txt     | 24 +++++++++++++++++++
>  1 file changed, 24 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/temperature/max31856.txt
> 
> diff --git a/Documentation/devicetree/bindings/iio/temperature/max31856.txt b/Documentation/devicetree/bindings/iio/temperature/max31856.txt
> new file mode 100644
> index 000000000000..06ab43bb4de8
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/temperature/max31856.txt
> @@ -0,0 +1,24 @@
> +Maxim MAX31856 thermocouple support
> +
> +https://datasheets.maximintegrated.com/en/ds/MAX31856.pdf
> +
> +Optional property:
> +	- thermocouple-type: Type of thermocouple (THERMOCOUPLE_TYPE_K if
> +		omitted). Supported types are B, E, J, K, N, R, S, T.
> +
> +Required properties:
> +	- compatible: must be "maxim,max31856"
> +	- reg: SPI chip select number for the device
> +	- spi-max-frequency: As per datasheet max. supported freq is 5000000
> +	- spi-cpha: must be defined for max31856 to enable SPI mode 1
> +
> +	Refer to spi/spi-bus.txt for generic SPI slave bindings.
> +
> + Example:
> +	temp-sensor@0 {
> +		compatible = "maxim,max31856";
> +		reg = <0>;
> +		spi-max-frequency = <5000000>;
> +		spi-cpha;
> +		thermocouple-type = <THERMOCOUPLE_TYPE_K>;
> +	};

[PATCH v7 3/3] iio:temperature: Add MAX31856 thermocouple support

[Patrick Havelange]

From: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>

This patch adds support for Maxim MAX31856 thermocouple
temperature sensor support.

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>
Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
---
Changes
v1 -> v2
[Peter
	1. Fixed all space & 'return' related comments
	2. Removed 'sysfs_create_group' api  because
	   iio_device_register function is handling sysfs entry
	3. Return -EIO if there is any fault
	4. Added check for 'read_size' before spi read call
	5. Removed license text from the source file
	6. Added .o file in alphabetic order
	7. Used #defines instead of magic bits

v2 -> v3
[Jonathan
	1. Used bool for fault_oc and fault_ovuv
	2. Changed 'max31856_read' function and use byte array to
	   store registers value.
	3. Used 'GENMASK' where required
        4. Changed logic 'max31856_thermocouple_read' function. Used
	   array to read registers value.
	5. Used 'devm_iio_device_register' and removed 'max31856_remove'.
	6. Fixed other cosmetic changes.
	7. Added 'sysfs-bus-iio-temperature-max31856' file and updated
	   'MAINTAINERS' file.

v3 -> v4
[Jonathan
	1. Removed unwanted logic
	2. Updated code to handle return value of max31856_read call
	3. Added devicetree id table
	4. Removed one-shot support from driver as this support was not
	   implemented with correct design.

v4 -> v5
[Patrick
	1. Rename thermocouple type to maxim,thermocouple-type for DT entry
	2. Don't cache values from the Fault Status Register
	3. Simplify a bit max31856_init()
	4. Use IIO_NO_MOD in switch case + default error case
	5. Use dev_*() instead of pr_*()
	6. Fix missing space in comments
	7. Removed iio_info.driver_module assignment as no longer present
	8. Don't keep read/write buffer into the internal driver struct
	9. Updated kernel version, add missing space in documentation
       10. Updated (c) year
       11. Removed linux/init.h #include
       12. More use of BIT() macro
       13. Removed iio_chan_spec.address assignment as not used
       14. In max31856_thermocouple_read(), same switch case order as
	   channels definition
       15. Refactor show_fault_*() functions
       16. Use u8 as register type in max31856_{read,write}()

v5 -> v6
[Patrick
	1. Use generic thermocouple-type property
	2. Fix doc for fault_ovuv entry
	3. Add check for supported thermocouple-types in probe()

v6 -> v7
[Patrick
	1. None
---
 .../sysfs-bus-iio-temperature-max31856        |  24 ++
 drivers/iio/temperature/Kconfig               |  10 +
 drivers/iio/temperature/Makefile              |   1 +
 drivers/iio/temperature/max31856.c            | 353 ++++++++++++++++++
 4 files changed, 388 insertions(+)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856
 create mode 100644 drivers/iio/temperature/max31856.c

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856 b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856
new file mode 100644
index 000000000000..3b3509a3ef2f
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856
@@ -0,0 +1,24 @@
+What:		/sys/bus/iio/devices/iio:deviceX/fault_oc
+KernelVersion:	5.1
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Open-circuit fault. The detection of open-circuit faults,
+		such as those caused by broken thermocouple wires.
+		Reading returns either '1' or '0'.
+		'1' = An open circuit such as broken thermocouple wires
+		      has been detected.
+		'0' = No open circuit or broken thermocouple wires are detected
+
+What:		/sys/bus/iio/devices/iio:deviceX/fault_ovuv
+KernelVersion:	5.1
+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 by integrated MOSFETs at the T+ and T- inputs, and the
+		BIAS output. These MOSFETs 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).
diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
index 82e4a62745e2..c66eeb23615b 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 34a31db0bb63..baca4776ca0d 100644
--- a/drivers/iio/temperature/Makefile
+++ b/drivers/iio/temperature/Makefile
@@ -5,6 +5,7 @@
 
 obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
 obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
+obj-$(CONFIG_MAX31856) += max31856.o
 obj-$(CONFIG_MLX90614) += mlx90614.o
 obj-$(CONFIG_MLX90632) += mlx90632.o
 obj-$(CONFIG_TMP006) += tmp006.o
diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
new file mode 100644
index 000000000000..6b67d6b95cf9
--- /dev/null
+++ b/drivers/iio/temperature/max31856.c
@@ -0,0 +1,353 @@
+// SPDX-License-Identifier: GPL-2.0
+/* max31856.c
+ *
+ * Maxim MAX31856 thermocouple sensor driver
+ *
+ * Copyright (C) 2018-2019 Rockwell Collins
+ */
+
+#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>
+#include <dt-bindings/iio/temperature/thermocouple.h>
+/*
+ * The MSB of the register value determines whether the following byte will
+ * be written or read. If it is 0, one or more byte reads will follow.
+ */
+#define MAX31856_RD_WR_BIT         BIT(7)
+
+#define MAX31856_CR0_AUTOCONVERT   BIT(7)
+#define MAX31856_CR0_1SHOT         BIT(6)
+#define MAX31856_CR0_OCFAULT       BIT(4)
+#define MAX31856_CR0_OCFAULT_MASK  GENMASK(5, 4)
+#define MAX31856_TC_TYPE_MASK      GENMASK(3, 0)
+#define MAX31856_FAULT_OVUV        BIT(1)
+#define MAX31856_FAULT_OPEN        BIT(0)
+
+/* 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,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+	},
+	{	/* Cold Junction Temperature */
+		.type = IIO_TEMP,
+		.channel2 = IIO_MOD_TEMP_AMBIENT,
+		.modified = 1,
+		.info_mask_separate =
+			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
+	},
+};
+
+struct max31856_data {
+	struct spi_device *spi;
+	u32 thermocouple_type;
+};
+
+static int max31856_read(struct max31856_data *data, u8 reg,
+			 u8 val[], unsigned int read_size)
+{
+	return spi_write_then_read(data->spi, &reg, 1, val, read_size);
+}
+
+static int max31856_write(struct max31856_data *data, u8 reg,
+			  unsigned int val)
+{
+	u8 buf[2];
+
+	buf[0] = reg | (MAX31856_RD_WR_BIT);
+	buf[1] = val;
+
+	return spi_write(data->spi, buf, 2);
+}
+
+static int max31856_init(struct max31856_data *data)
+{
+	int ret;
+	u8 reg_cr0_val, reg_cr1_val;
+
+	/* Start by changing to Off mode before making changes as
+	 * some settings are recommended to be set only when the device
+	 * is off
+	 */
+	ret = max31856_read(data, MAX31856_CR0_REG, &reg_cr0_val, 1);
+	if (ret)
+		return ret;
+
+	reg_cr0_val &= ~MAX31856_CR0_AUTOCONVERT;
+	ret = max31856_write(data, MAX31856_CR0_REG, reg_cr0_val);
+	if (ret)
+		return ret;
+
+	/* Set thermocouple type based on dts property */
+	ret = max31856_read(data, MAX31856_CR1_REG, &reg_cr1_val, 1);
+	if (ret)
+		return ret;
+
+	reg_cr1_val &= ~MAX31856_TC_TYPE_MASK;
+	reg_cr1_val |= data->thermocouple_type;
+	ret = max31856_write(data, MAX31856_CR1_REG, reg_cr1_val);
+	if (ret)
+		return ret;
+
+	/*
+	 * Enable Open circuit fault detection
+	 * Read datasheet for more information: Table 4.
+	 * Value 01 means : Enabled (Once every 16 conversions)
+	 */
+	reg_cr0_val &= ~MAX31856_CR0_OCFAULT_MASK;
+	reg_cr0_val |= MAX31856_CR0_OCFAULT;
+
+	/* Set Auto Conversion Mode */
+	reg_cr0_val &= ~MAX31856_CR0_1SHOT;
+	reg_cr0_val |= MAX31856_CR0_AUTOCONVERT;
+
+	return max31856_write(data, MAX31856_CR0_REG, reg_cr0_val);
+}
+
+static int max31856_thermocouple_read(struct max31856_data *data,
+				      struct iio_chan_spec const *chan,
+				      int *val)
+{
+	int ret, offset_cjto;
+	u8 reg_val[3];
+
+	switch (chan->channel2) {
+	case IIO_NO_MOD:
+		/*
+		 * Multibyte Read
+		 * MAX31856_LTCBH_REG, MAX31856_LTCBM_REG, MAX31856_LTCBL_REG
+		 */
+		ret = max31856_read(data, MAX31856_LTCBH_REG, reg_val, 3);
+		if (ret)
+			return ret;
+		/* Skip last 5 dead bits of LTCBL */
+		*val = (reg_val[0] << 16 | reg_val[1] << 8 | reg_val[2]) >> 5;
+		/* Check 7th bit of LTCBH reg. value for sign*/
+		if (reg_val[0] & 0x80)
+			*val -= 0x80000;
+		break;
+
+	case IIO_MOD_TEMP_AMBIENT:
+		/*
+		 * Multibyte Read
+		 * MAX31856_CJTO_REG, MAX31856_CJTH_REG, MAX31856_CJTL_REG
+		 */
+		ret = max31856_read(data, MAX31856_CJTO_REG, reg_val, 3);
+		if (ret)
+			return ret;
+		/* Get Cold Junction Temp. offset register value */
+		offset_cjto = reg_val[0];
+		/* Get CJTH and CJTL value and skip last 2 dead bits of CJTL */
+		*val = (reg_val[1] << 8 | reg_val[2]) >> 2;
+		/* As per datasheet add offset into CJTH and CJTL */
+		*val += offset_cjto;
+		/* Check 7th bit of CJTH reg. value for sign */
+		if (reg_val[1] & 0x80)
+			*val -= 0x4000;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	ret = max31856_read(data, MAX31856_SR_REG, reg_val, 1);
+	if (ret)
+		return ret;
+	/* Check for over/under voltage or open circuit fault */
+	if (reg_val[0] & (MAX31856_FAULT_OVUV | MAX31856_FAULT_OPEN))
+		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;
+
+	switch (mask) {
+	case IIO_CHAN_INFO_RAW:
+		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) */
+			return IIO_VAL_INT_PLUS_MICRO;
+		}
+		break;
+	}
+
+	return ret;
+}
+
+static ssize_t show_fault(struct device *dev, u8 faultbit, char *buf)
+{
+	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
+	struct max31856_data *data = iio_priv(indio_dev);
+	u8 reg_val;
+	int ret;
+	bool fault;
+
+	ret = max31856_read(data, MAX31856_SR_REG, &reg_val, 1);
+	if (ret)
+		return ret;
+
+	fault = reg_val & 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, MAX31856_FAULT_OVUV, buf);
+}
+
+static ssize_t show_fault_oc(struct device *dev,
+			     struct device_attribute *attr,
+			     char *buf)
+{
+	return show_fault(dev, MAX31856_FAULT_OPEN, buf);
+}
+
+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 const struct iio_info max31856_info = {
+	.read_raw = max31856_read_raw,
+	.attrs = &max31856_group,
+};
+
+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);
+
+	ret = of_property_read_u32(spi->dev.of_node, "thermocouple-type",
+				   &data->thermocouple_type);
+
+	if (ret) {
+		dev_info(&spi->dev,
+			 "Could not read thermocouple type DT property, configuring as a K-Type\n");
+		data->thermocouple_type = THERMOCOUPLE_TYPE_K;
+	}
+
+	/*
+	 * no need to translate values as the supported types
+	 * have the same value as the #defines
+	 */
+	switch (data->thermocouple_type) {
+	case THERMOCOUPLE_TYPE_B:
+	case THERMOCOUPLE_TYPE_E:
+	case THERMOCOUPLE_TYPE_J:
+	case THERMOCOUPLE_TYPE_K:
+	case THERMOCOUPLE_TYPE_N:
+	case THERMOCOUPLE_TYPE_R:
+	case THERMOCOUPLE_TYPE_S:
+	case THERMOCOUPLE_TYPE_T:
+		break;
+	default:
+		dev_err(&spi->dev,
+			"error: thermocouple-type %u not supported by max31856\n"
+			, data->thermocouple_type);
+		return -EINVAL;
+	}
+
+	ret = max31856_init(data);
+	if (ret) {
+		dev_err(&spi->dev, "error: Failed to configure max31856\n");
+		return ret;
+	}
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
+}
+
+static const struct spi_device_id max31856_id[] = {
+	{ "max31856", 0 },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, max31856_id);
+
+static const struct of_device_id max31856_of_match[] = {
+	{ .compatible = "maxim,max31856" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max31856_of_match);
+
+static struct spi_driver max31856_driver = {
+	.driver = {
+		.name = "max31856",
+		.of_match_table = max31856_of_match,
+	},
+	.probe = max31856_probe,
+	.id_table = max31856_id,
+};
+module_spi_driver(max31856_driver);
+
+MODULE_AUTHOR("Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>");
+MODULE_AUTHOR("Patrick Havelange <patrick.havelange@essensium.com>");
+MODULE_DESCRIPTION("Maxim MAX31856 thermocouple sensor driver");
+MODULE_LICENSE("GPL");
-- 
2.19.1

Re: [PATCH v7 3/3] iio:temperature: Add MAX31856 thermocouple support

[Jonathan Cameron]

On Tue, 26 Mar 2019 12:18:42 +0100
Patrick Havelange <patrick.havelange@essensium.com> wrote:

> From: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
> 
> This patch adds support for Maxim MAX31856 thermocouple
> temperature sensor support.
> 
> 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>
> Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
> Changes
> v1 -> v2
> [Peter
> 	1. Fixed all space & 'return' related comments
> 	2. Removed 'sysfs_create_group' api  because
> 	   iio_device_register function is handling sysfs entry
> 	3. Return -EIO if there is any fault
> 	4. Added check for 'read_size' before spi read call
> 	5. Removed license text from the source file
> 	6. Added .o file in alphabetic order
> 	7. Used #defines instead of magic bits
> 
> v2 -> v3
> [Jonathan
> 	1. Used bool for fault_oc and fault_ovuv
> 	2. Changed 'max31856_read' function and use byte array to
> 	   store registers value.
> 	3. Used 'GENMASK' where required
>         4. Changed logic 'max31856_thermocouple_read' function. Used
> 	   array to read registers value.
> 	5. Used 'devm_iio_device_register' and removed 'max31856_remove'.
> 	6. Fixed other cosmetic changes.
> 	7. Added 'sysfs-bus-iio-temperature-max31856' file and updated
> 	   'MAINTAINERS' file.
> 
> v3 -> v4
> [Jonathan
> 	1. Removed unwanted logic
> 	2. Updated code to handle return value of max31856_read call
> 	3. Added devicetree id table
> 	4. Removed one-shot support from driver as this support was not
> 	   implemented with correct design.
> 
> v4 -> v5
> [Patrick
> 	1. Rename thermocouple type to maxim,thermocouple-type for DT entry
> 	2. Don't cache values from the Fault Status Register
> 	3. Simplify a bit max31856_init()
> 	4. Use IIO_NO_MOD in switch case + default error case
> 	5. Use dev_*() instead of pr_*()
> 	6. Fix missing space in comments
> 	7. Removed iio_info.driver_module assignment as no longer present
> 	8. Don't keep read/write buffer into the internal driver struct
> 	9. Updated kernel version, add missing space in documentation
>        10. Updated (c) year
>        11. Removed linux/init.h #include
>        12. More use of BIT() macro
>        13. Removed iio_chan_spec.address assignment as not used
>        14. In max31856_thermocouple_read(), same switch case order as
> 	   channels definition
>        15. Refactor show_fault_*() functions
>        16. Use u8 as register type in max31856_{read,write}()
> 
> v5 -> v6
> [Patrick
> 	1. Use generic thermocouple-type property
> 	2. Fix doc for fault_ovuv entry
> 	3. Add check for supported thermocouple-types in probe()
> 
> v6 -> v7
> [Patrick
> 	1. None
> ---
>  .../sysfs-bus-iio-temperature-max31856        |  24 ++
>  drivers/iio/temperature/Kconfig               |  10 +
>  drivers/iio/temperature/Makefile              |   1 +
>  drivers/iio/temperature/max31856.c            | 353 ++++++++++++++++++
>  4 files changed, 388 insertions(+)
>  create mode 100644 Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856
>  create mode 100644 drivers/iio/temperature/max31856.c
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856 b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856
> new file mode 100644
> index 000000000000..3b3509a3ef2f
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-temperature-max31856
> @@ -0,0 +1,24 @@
> +What:		/sys/bus/iio/devices/iio:deviceX/fault_oc
> +KernelVersion:	5.1
> +Contact:	linux-iio@vger.kernel.org
> +Description:
> +		Open-circuit fault. The detection of open-circuit faults,
> +		such as those caused by broken thermocouple wires.
> +		Reading returns either '1' or '0'.
> +		'1' = An open circuit such as broken thermocouple wires
> +		      has been detected.
> +		'0' = No open circuit or broken thermocouple wires are detected
> +
> +What:		/sys/bus/iio/devices/iio:deviceX/fault_ovuv
> +KernelVersion:	5.1
> +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 by integrated MOSFETs at the T+ and T- inputs, and the
> +		BIAS output. These MOSFETs 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).
> diff --git a/drivers/iio/temperature/Kconfig b/drivers/iio/temperature/Kconfig
> index 82e4a62745e2..c66eeb23615b 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 34a31db0bb63..baca4776ca0d 100644
> --- a/drivers/iio/temperature/Makefile
> +++ b/drivers/iio/temperature/Makefile
> @@ -5,6 +5,7 @@
>  
>  obj-$(CONFIG_HID_SENSOR_TEMP) += hid-sensor-temperature.o
>  obj-$(CONFIG_MAXIM_THERMOCOUPLE) += maxim_thermocouple.o
> +obj-$(CONFIG_MAX31856) += max31856.o
>  obj-$(CONFIG_MLX90614) += mlx90614.o
>  obj-$(CONFIG_MLX90632) += mlx90632.o
>  obj-$(CONFIG_TMP006) += tmp006.o
> diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
> new file mode 100644
> index 000000000000..6b67d6b95cf9
> --- /dev/null
> +++ b/drivers/iio/temperature/max31856.c
> @@ -0,0 +1,353 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* max31856.c
> + *
> + * Maxim MAX31856 thermocouple sensor driver
> + *
> + * Copyright (C) 2018-2019 Rockwell Collins
> + */
> +
> +#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>
> +#include <dt-bindings/iio/temperature/thermocouple.h>
> +/*
> + * The MSB of the register value determines whether the following byte will
> + * be written or read. If it is 0, one or more byte reads will follow.
> + */
> +#define MAX31856_RD_WR_BIT         BIT(7)
> +
> +#define MAX31856_CR0_AUTOCONVERT   BIT(7)
> +#define MAX31856_CR0_1SHOT         BIT(6)
> +#define MAX31856_CR0_OCFAULT       BIT(4)
> +#define MAX31856_CR0_OCFAULT_MASK  GENMASK(5, 4)
> +#define MAX31856_TC_TYPE_MASK      GENMASK(3, 0)
> +#define MAX31856_FAULT_OVUV        BIT(1)
> +#define MAX31856_FAULT_OPEN        BIT(0)
> +
> +/* 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,
> +		.info_mask_separate =
> +			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +	},
> +	{	/* Cold Junction Temperature */
> +		.type = IIO_TEMP,
> +		.channel2 = IIO_MOD_TEMP_AMBIENT,
> +		.modified = 1,
> +		.info_mask_separate =
> +			BIT(IIO_CHAN_INFO_RAW) | BIT(IIO_CHAN_INFO_SCALE),
> +	},
> +};
> +
> +struct max31856_data {
> +	struct spi_device *spi;
> +	u32 thermocouple_type;
> +};
> +
> +static int max31856_read(struct max31856_data *data, u8 reg,
> +			 u8 val[], unsigned int read_size)
> +{
> +	return spi_write_then_read(data->spi, &reg, 1, val, read_size);
> +}
> +
> +static int max31856_write(struct max31856_data *data, u8 reg,
> +			  unsigned int val)
> +{
> +	u8 buf[2];
> +
> +	buf[0] = reg | (MAX31856_RD_WR_BIT);
> +	buf[1] = val;
> +
> +	return spi_write(data->spi, buf, 2);
> +}
> +
> +static int max31856_init(struct max31856_data *data)
> +{
> +	int ret;
> +	u8 reg_cr0_val, reg_cr1_val;
> +
> +	/* Start by changing to Off mode before making changes as
> +	 * some settings are recommended to be set only when the device
> +	 * is off
> +	 */
> +	ret = max31856_read(data, MAX31856_CR0_REG, &reg_cr0_val, 1);
> +	if (ret)
> +		return ret;
> +
> +	reg_cr0_val &= ~MAX31856_CR0_AUTOCONVERT;
> +	ret = max31856_write(data, MAX31856_CR0_REG, reg_cr0_val);
> +	if (ret)
> +		return ret;
> +
> +	/* Set thermocouple type based on dts property */
> +	ret = max31856_read(data, MAX31856_CR1_REG, &reg_cr1_val, 1);
> +	if (ret)
> +		return ret;
> +
> +	reg_cr1_val &= ~MAX31856_TC_TYPE_MASK;
> +	reg_cr1_val |= data->thermocouple_type;
> +	ret = max31856_write(data, MAX31856_CR1_REG, reg_cr1_val);
> +	if (ret)
> +		return ret;
> +
> +	/*
> +	 * Enable Open circuit fault detection
> +	 * Read datasheet for more information: Table 4.
> +	 * Value 01 means : Enabled (Once every 16 conversions)
> +	 */
> +	reg_cr0_val &= ~MAX31856_CR0_OCFAULT_MASK;
> +	reg_cr0_val |= MAX31856_CR0_OCFAULT;
> +
> +	/* Set Auto Conversion Mode */
> +	reg_cr0_val &= ~MAX31856_CR0_1SHOT;
> +	reg_cr0_val |= MAX31856_CR0_AUTOCONVERT;
> +
> +	return max31856_write(data, MAX31856_CR0_REG, reg_cr0_val);
> +}
> +
> +static int max31856_thermocouple_read(struct max31856_data *data,
> +				      struct iio_chan_spec const *chan,
> +				      int *val)
> +{
> +	int ret, offset_cjto;
> +	u8 reg_val[3];
> +
> +	switch (chan->channel2) {
> +	case IIO_NO_MOD:
> +		/*
> +		 * Multibyte Read
> +		 * MAX31856_LTCBH_REG, MAX31856_LTCBM_REG, MAX31856_LTCBL_REG
> +		 */
> +		ret = max31856_read(data, MAX31856_LTCBH_REG, reg_val, 3);
> +		if (ret)
> +			return ret;
> +		/* Skip last 5 dead bits of LTCBL */
> +		*val = (reg_val[0] << 16 | reg_val[1] << 8 | reg_val[2]) >> 5;
> +		/* Check 7th bit of LTCBH reg. value for sign*/
> +		if (reg_val[0] & 0x80)
> +			*val -= 0x80000;
> +		break;
> +
> +	case IIO_MOD_TEMP_AMBIENT:
> +		/*
> +		 * Multibyte Read
> +		 * MAX31856_CJTO_REG, MAX31856_CJTH_REG, MAX31856_CJTL_REG
> +		 */
> +		ret = max31856_read(data, MAX31856_CJTO_REG, reg_val, 3);
> +		if (ret)
> +			return ret;
> +		/* Get Cold Junction Temp. offset register value */
> +		offset_cjto = reg_val[0];
> +		/* Get CJTH and CJTL value and skip last 2 dead bits of CJTL */
> +		*val = (reg_val[1] << 8 | reg_val[2]) >> 2;
> +		/* As per datasheet add offset into CJTH and CJTL */
> +		*val += offset_cjto;
> +		/* Check 7th bit of CJTH reg. value for sign */
> +		if (reg_val[1] & 0x80)
> +			*val -= 0x4000;
> +		break;
> +
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	ret = max31856_read(data, MAX31856_SR_REG, reg_val, 1);
> +	if (ret)
> +		return ret;
> +	/* Check for over/under voltage or open circuit fault */
> +	if (reg_val[0] & (MAX31856_FAULT_OVUV | MAX31856_FAULT_OPEN))
> +		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;
> +
> +	switch (mask) {
> +	case IIO_CHAN_INFO_RAW:
> +		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) */
> +			return IIO_VAL_INT_PLUS_MICRO;
> +		}
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
> +static ssize_t show_fault(struct device *dev, u8 faultbit, char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct max31856_data *data = iio_priv(indio_dev);
> +	u8 reg_val;
> +	int ret;
> +	bool fault;
> +
> +	ret = max31856_read(data, MAX31856_SR_REG, &reg_val, 1);
> +	if (ret)
> +		return ret;
> +
> +	fault = reg_val & 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, MAX31856_FAULT_OVUV, buf);
> +}
> +
> +static ssize_t show_fault_oc(struct device *dev,
> +			     struct device_attribute *attr,
> +			     char *buf)
> +{
> +	return show_fault(dev, MAX31856_FAULT_OPEN, buf);
> +}
> +
> +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 const struct iio_info max31856_info = {
> +	.read_raw = max31856_read_raw,
> +	.attrs = &max31856_group,
> +};
> +
> +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);
> +
> +	ret = of_property_read_u32(spi->dev.of_node, "thermocouple-type",
> +				   &data->thermocouple_type);
> +
> +	if (ret) {
> +		dev_info(&spi->dev,
> +			 "Could not read thermocouple type DT property, configuring as a K-Type\n");
> +		data->thermocouple_type = THERMOCOUPLE_TYPE_K;
> +	}
> +
> +	/*
> +	 * no need to translate values as the supported types
> +	 * have the same value as the #defines
> +	 */
> +	switch (data->thermocouple_type) {
> +	case THERMOCOUPLE_TYPE_B:
> +	case THERMOCOUPLE_TYPE_E:
> +	case THERMOCOUPLE_TYPE_J:
> +	case THERMOCOUPLE_TYPE_K:
> +	case THERMOCOUPLE_TYPE_N:
> +	case THERMOCOUPLE_TYPE_R:
> +	case THERMOCOUPLE_TYPE_S:
> +	case THERMOCOUPLE_TYPE_T:
> +		break;
> +	default:
> +		dev_err(&spi->dev,
> +			"error: thermocouple-type %u not supported by max31856\n"
> +			, data->thermocouple_type);
> +		return -EINVAL;
> +	}
> +
> +	ret = max31856_init(data);
> +	if (ret) {
> +		dev_err(&spi->dev, "error: Failed to configure max31856\n");
> +		return ret;
> +	}
> +
> +	return devm_iio_device_register(&spi->dev, indio_dev);
> +}
> +
> +static const struct spi_device_id max31856_id[] = {
> +	{ "max31856", 0 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(spi, max31856_id);
> +
> +static const struct of_device_id max31856_of_match[] = {
> +	{ .compatible = "maxim,max31856" },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(of, max31856_of_match);
> +
> +static struct spi_driver max31856_driver = {
> +	.driver = {
> +		.name = "max31856",
> +		.of_match_table = max31856_of_match,
> +	},
> +	.probe = max31856_probe,
> +	.id_table = max31856_id,
> +};
> +module_spi_driver(max31856_driver);
> +
> +MODULE_AUTHOR("Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>");
> +MODULE_AUTHOR("Patrick Havelange <patrick.havelange@essensium.com>");
> +MODULE_DESCRIPTION("Maxim MAX31856 thermocouple sensor driver");
> +MODULE_LICENSE("GPL");

Re: [PATCH v7 1/3] dt-bindings: iio/temperature: Add thermocouple types (and doc)

[Jonathan Cameron]

On Tue, 26 Mar 2019 12:18:40 +0100
Patrick Havelange <patrick.havelange@essensium.com> wrote:

> This patch introduces common thermocouple types used by various
> temperature sensors. Also a brief documentation explaining this
> "thermocouple-type" property.
> 
> Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
You have addressed all of Rob's feedback I think, so I'll not pester
Rob for any follow up (always welcome of course if he wants to give it!)

Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> ---
> Changes v7
>  - Merge header and doc in same patch
>  - Doc:add it's a single cell entry
>  - Doc:removed non complete example
> 
> Changes v6
>  - Add this file
> ---
>  .../iio/temperature/temperature-bindings.txt     |  7 +++++++
>  .../dt-bindings/iio/temperature/thermocouple.h   | 16 ++++++++++++++++
>  2 files changed, 23 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt
>  create mode 100644 include/dt-bindings/iio/temperature/thermocouple.h
> 
> diff --git a/Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt b/Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt
> new file mode 100644
> index 000000000000..8f339cab74ae
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iio/temperature/temperature-bindings.txt
> @@ -0,0 +1,7 @@
> +If the temperature sensor device can be configured to use some specific
> +thermocouple type, you can use the defined types provided in the file
> +"include/dt-bindings/iio/temperature/thermocouple.h".
> +
> +Property:
> +thermocouple-type:	A single cell representing the type of the thermocouple
> +			used by the device.
> diff --git a/include/dt-bindings/iio/temperature/thermocouple.h b/include/dt-bindings/iio/temperature/thermocouple.h
> new file mode 100644
> index 000000000000..ce037f5238ac
> --- /dev/null
> +++ b/include/dt-bindings/iio/temperature/thermocouple.h
> @@ -0,0 +1,16 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _DT_BINDINGS_TEMPERATURE_THERMOCOUPLE_H
> +#define _DT_BINDINGS_TEMPERATURE_THERMOCOUPLE_H
> +
> +
> +#define THERMOCOUPLE_TYPE_B	0x00
> +#define THERMOCOUPLE_TYPE_E	0x01
> +#define THERMOCOUPLE_TYPE_J	0x02
> +#define THERMOCOUPLE_TYPE_K	0x03
> +#define THERMOCOUPLE_TYPE_N	0x04
> +#define THERMOCOUPLE_TYPE_R	0x05
> +#define THERMOCOUPLE_TYPE_S	0x06
> +#define THERMOCOUPLE_TYPE_T	0x07
> +
> +#endif /* _DT_BINDINGS_TEMPERATURE_THERMOCOUPLE_H */