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

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

Il giorno gio 17 ott 2019 alle ore 14:36 Jonathan Cameron
<jonathan.cameron@huawei.com> ha scritto:
>
> On Wed, 16 Oct 2019 15:43:18 +0200
> Andrea Merello <andrea.merello@gmail.com> wrote:
>
> > 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.
> >
>
> Lets do it then ;)  We might want to add a read only attrs to the
> other drivers to make them self describing.

Seems good!
Will do.

> Thanks,
>
> Jonathan
>
> > > 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,
> > > >  };
> > > >
> > >
>
>