Re: [PATCH 3/3] iio: max31856: add support for runtime-configuring the thermocouple type

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 23 Sep 2019 14:17:14 +0200
Andrea Merello <andrea.merello@gmail.com> wrote:

> The sensor support various thermocouple types (e.g. J, K, N, ...). The
> driver allows to configure this parameter using a DT property.
> 
> This is useful when i.e. the thermocouple is physically tied to the sensor
> and it is usually not removed, or when it is at least known in advace

advance

> which sensor will be connected to the circuit.
> 
> However, if the user can randomly connect any kind of thermocouples (i.e.
> the device exposes a connector, and the user is free to connect its own
> sensors), it would be more appropriate to provide a mechanism to
> dynamically switch from one thermocouple type to another. This can be i.e.
> handled in userspace by a GUI, a configuration file or a program that
> detects the thermocouple type by reading a GPIO, or a eeprom on the probe,
> or whatever.
> 
> This patch adds a IIO attribute that can be used to override, at run-time,
> the DT-provided setting (which serves as default).
> 
> Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
For now this is device specific ABI so you need to have an entry in
Documentation/ABI/testing/sysfs-bus-iio-max31856

Or we could consider this generic enough to put it in a file
covering other thermocouple to digital sensors.

Thanks,

Jonathan

> ---
>  drivers/iio/temperature/max31856.c | 44 ++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
> index 8b2e0102fa5c..588e791c79a3 100644
> --- a/drivers/iio/temperature/max31856.c
> +++ b/drivers/iio/temperature/max31856.c
> @@ -6,6 +6,7 @@
>   * Copyright (C) 2018-2019 Rockwell Collins
>   */
>  
> +#include <linux/ctype.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/err.h>
> @@ -70,6 +71,10 @@ struct max31856_data {
>  	int averaging;
>  };
>  
> +const char max31856_tc_types[] = {
> +	'B', 'E', 'J', 'K', 'N', 'R', 'S', 'T'
> +};
> +
>  static int max31856_read(struct max31856_data *data, u8 reg,
>  			 u8 val[], unsigned int read_size)
>  {
> @@ -336,16 +341,55 @@ static ssize_t set_averaging(struct device *dev,
>  	return len;
>  }
>  
> +static ssize_t show_tc_type(struct device *dev,
> +			    struct device_attribute *attr,
> +			    char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct max31856_data *data = iio_priv(indio_dev);
> +
> +	return sprintf(buf, "%c\n", max31856_tc_types[data->thermocouple_type]);
> +}
> +
> +static ssize_t set_tc_type(struct device *dev,
> +			   struct device_attribute *attr,
> +			   const char *buf,
> +			   size_t len)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct max31856_data *data = iio_priv(indio_dev);
> +	char tmp;
> +	int tc_type = -1;
> +	int i;
> +
> +	if (sscanf(buf, "%c\n", &tmp) != 1)
> +		return -EINVAL;
> +
> +	for (i = 0; i < ARRAY_SIZE(max31856_tc_types); i++) {
> +		if (max31856_tc_types[i] == toupper(tmp)) {
> +			tc_type = i;
> +			break;
> +		}
> +	}
> +	if (tc_type < 0)
> +		return -EINVAL;
> +	data->thermocouple_type = tc_type;
> +	max31856_init(data);
> +	return len;
> +}
> +
>  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 IIO_DEVICE_ATTR(filter, 0644, show_filter, set_filter, 0);
>  static IIO_DEVICE_ATTR(averaging, 0644, show_averaging, set_averaging, 0);
> +static IIO_DEVICE_ATTR(thermocouple_type, 0644, show_tc_type, set_tc_type, 0);
>  
>  static struct attribute *max31856_attributes[] = {
>  	&iio_dev_attr_fault_ovuv.dev_attr.attr,
>  	&iio_dev_attr_fault_oc.dev_attr.attr,
>  	&iio_dev_attr_filter.dev_attr.attr,
>  	&iio_dev_attr_averaging.dev_attr.attr,
> +	&iio_dev_attr_thermocouple_type.dev_attr.attr,
>  	NULL,
>  };
>