On Mon, 23 Sep 2019 14:17:12 +0200
Andrea Merello <andrea.merello@xxxxxxxxx> 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.
>
> Signed-off-by: Andrea Merello <andrea.merello@xxxxxxxxx>
This one is not something that can be expect to be known from the setup
of the device as it will depend on local mains frequency.
So fine, to have it as a userspace control, but the name is too generic.
We already have a number of filter attributes and we should try to
work out how to bring it inline with them.
in_X_filter_low_pass_3db_frequency
in_X_filter_high_pass_3db_frequency
So would,
in_X_filter_notch_center_frequency work?
( I suppose we should use the American spelling ;)
This kind of ignores the harmonics aspect but at least documents the
main frequency being blocked.
There is a slight complexity that we have devices that have dual
notchfilters (50 and 60Hz) and ones where you can turn it off entirely.
I suppose no value would count as off and we could perhaps use a list
for both on at the same time (though that's a bit horrible).
> ---
> drivers/iio/temperature/max31856.c | 49 ++++++++++++++++++++++++++++++
> 1 file changed, 49 insertions(+)
>
> diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
> index 73ed550e3fc9..d12613f7ba3c 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 +256,53 @@ 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(filter, 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_filter.dev_attr.attr,
> NULL,
> };
>
> @@ -280,6 +328,7 @@ 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);
>
