Re: [v2 1/9] iio: max31856: add option for setting mains filter rejection frequency

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 12 Nov 2019 07:59:19 +0900
Matt Ranostay <matt.ranostay@konsulko.com> wrote:

> On Tue, Nov 12, 2019 at 12:35 AM Andrea Merello
> <andrea.merello@gmail.com> wrote:
> >
> > This sensor has an embedded notch filter for reducing interferences caused
> > by the power mains. This filter can be tuned to reject either 50Hz or 60Hz
> > (and harmonics).
> >
> > Currently the said setting is left alone (the sensor defaults to 60Hz).
> > This patch introduces a IIO attribute that allows the user to set the said
> > filter to the desired frequency.
> >
> > NOTE: this has been intentionally not tied to any DT property to allow
> > the configuration of this setting from userspace, e.g. with a GUI or by
> > reading a configuration file, or maybe reading a GPIO tied to a physical
> > switch or accessing some device that can autodetect the line frequency.
> >  
> 
> Looks good to me. Although this ideal could be a device tree property
> as well, but not a big deal.
> 
> Reviewed-by: Matt Ranostay <matt.ranostay@konsulko.com>
I've no objection to someone following up with DT support for this
as they might have a device that only supports one frequency of powersupply.
However, let's leave it until we have a user that cares.

I'm going to let the patch sit on the list a little longer though as
it introduces new ABI and others may want to review.

If I seem to have lost it in 2 weeks time give me a ping
(normally I don't lose patches, but it's happened a few times in the past!)

Thanks,

Jonathan

> 
> > Cc: Hartmut Knaack <knaack.h@gmx.de>
> > Cc: Lars-Peter Clausen <lars@metafoo.de>
> > Cc: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
> > Cc: Colin Ian King <colin.king@canonical.com>
> > Cc: Patrick Havelange <patrick.havelange@essensium.com>
> > Cc: Paresh Chaudhary <paresh.chaudhary@rockwellcollins.com>
> > Cc: Matt Weber <matthew.weber@rockwellcollins.com>
> > Cc: Matt Ranostay <matt.ranostay@konsulko.com>
> > Cc: Chuhong Yuan <hslester96@gmail.com>
> > Cc: Daniel Gomez <dagmcr@gmail.com>
> > Cc: linux-iio@vger.kernel.org
> > Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
> > ---
> >  drivers/iio/temperature/max31856.c | 50 ++++++++++++++++++++++++++++++
> >  1 file changed, 50 insertions(+)
> >
> > diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
> > index 73ed550e3fc9..d97ba9ee1598 100644
> > --- a/drivers/iio/temperature/max31856.c
> > +++ b/drivers/iio/temperature/max31856.c
> > @@ -23,6 +23,7 @@
> >  #define MAX31856_CR0_1SHOT         BIT(6)
> >  #define MAX31856_CR0_OCFAULT       BIT(4)
> >  #define MAX31856_CR0_OCFAULT_MASK  GENMASK(5, 4)
> > +#define MAX31856_CR0_FILTER_50HZ   BIT(0)
> >  #define MAX31856_TC_TYPE_MASK      GENMASK(3, 0)
> >  #define MAX31856_FAULT_OVUV        BIT(1)
> >  #define MAX31856_FAULT_OPEN        BIT(0)
> > @@ -63,6 +64,7 @@ static const struct iio_chan_spec max31856_channels[] = {
> >  struct max31856_data {
> >         struct spi_device *spi;
> >         u32 thermocouple_type;
> > +       bool filter_50hz;
> >  };
> >
> >  static int max31856_read(struct max31856_data *data, u8 reg,
> > @@ -123,6 +125,11 @@ static int max31856_init(struct max31856_data *data)
> >         reg_cr0_val &= ~MAX31856_CR0_1SHOT;
> >         reg_cr0_val |= MAX31856_CR0_AUTOCONVERT;
> >
> > +       if (data->filter_50hz)
> > +               reg_cr0_val |= MAX31856_CR0_FILTER_50HZ;
> > +       else
> > +               reg_cr0_val &= ~MAX31856_CR0_FILTER_50HZ;
> > +
> >         return max31856_write(data, MAX31856_CR0_REG, reg_cr0_val);
> >  }
> >
> > @@ -249,12 +256,54 @@ static ssize_t show_fault_oc(struct device *dev,
> >         return show_fault(dev, MAX31856_FAULT_OPEN, buf);
> >  }
> >
> > +static ssize_t show_filter(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, "%d\n", data->filter_50hz ? 50 : 60);
> > +}
> > +
> > +static ssize_t set_filter(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);
> > +       unsigned int freq;
> > +       int ret;
> > +
> > +       ret = kstrtouint(buf, 10, &freq);
> > +       if (ret)
> > +               return ret;
> > +
> > +       switch (freq) {
> > +       case 50:
> > +               data->filter_50hz = true;
> > +               break;
> > +       case 60:
> > +               data->filter_50hz = false;
> > +               break;
> > +       default:
> > +               return -EINVAL;
> > +       }
> > +
> > +       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(in_temp_filter_notch_center_frequency, 0644,
> > +                      show_filter, set_filter, 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_in_temp_filter_notch_center_frequency.dev_attr.attr,
> >         NULL,
> >  };
> >
> > @@ -280,6 +329,7 @@ static int max31856_probe(struct spi_device *spi)
> >
> >         data = iio_priv(indio_dev);
> >         data->spi = spi;
> > +       data->filter_50hz = false;
> >
> >         spi_set_drvdata(spi, indio_dev);
> >
> > --
> > 2.17.1
> >