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

[Andrea Merello <andrea.merello@gmail.com>]

Il giorno dom 6 ott 2019 alle ore 09:58 Jonathan Cameron
<jic23@kernel.org> ha scritto:
>
> 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

OK

> > 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

OK

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

Yes, theoretically thermocouple-type is a generic thing that isn't
bound to this specific driver/chip. Currently the others IIO
thermocouple drivers don't need this because they supports chips that
handle just a specific thermocouple type, but if you want to make this
API generic for the future then I can go this way.. It seems
reasonable to me indeed.

> 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,
> >  };
> >
>