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

From: Jonathan Cameron
Date: Sat Mar 30 2019 - 13:54:00 EST

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

> From: Paresh Chaudhary <paresh.chaudhary@xxxxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Matt Weber <matthew.weber@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Patrick Havelange <patrick.havelange@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx
> +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@xxxxxxxxxxxxxxx
> +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@xxxxxxxxxxxxxxxxxxx>");
> +MODULE_AUTHOR("Patrick Havelange <patrick.havelange@xxxxxxxxxxxxx>");
> +MODULE_DESCRIPTION("Maxim MAX31856 thermocouple sensor driver");
> +MODULE_LICENSE("GPL");