Re: [PATCH v1 15/15] iio: adc: ad7768-1: add filter type and decimation rate attributes

[Marcelo Schmitt <marcelo.schmitt1@gmail.com>]

On 01/07, Jonathan Santos wrote:
> Separate filter type and decimation rate from the sampling frequency
> attribute. The new filter type attribute enables SINC3 and WIDEBAND
> filters, which were previously unavailable.
> 
> Previously, combining decimation and MCLK divider in the sampling
> frequency obscured performance trade-offs. Lower MCLK divider
> settings increase power usage, while lower decimation rates reduce
> precision by decreasing averaging. By creating a decimation attribute,
> users gain finer control over performance.

If not going to use -3dB ABI instead of decimation rate thing, maybe throw the
formula for the sampling frequency here (or near its use in the code) to help
make the relation between samp_freq, master clock divider, and decimation rate
clearer?
Is it samp_freq = mclk / (mclk_div * dec_rate) ?

> 
> The addition of those attributes allows a wider range of sampling
> frequencies and more access to the device features.
> 
> Co-developed-by: PopPaul2021 <paul.pop@analog.com>
> Signed-off-by: PopPaul2021 <paul.pop@analog.com>
> Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
> ---
>  drivers/iio/adc/ad7768-1.c | 429 +++++++++++++++++++++++++++++++------
...
> +static const int dec_rate_values[6] = {
> +	32, 64, 128, 256, 512, 1024,
> +};
> +
> +static const  int sinc3_dec_rate_max_values[4] = {
> +	20480, 40960, 81920, 163840,
> +};
sinc3_dec_rate_max_values unused?

> +
> +static const char * const ad7768_filter_enum[] = {
> +	"sinc5", "sinc3", "wideband"
>  };
>  
...
> +static int ad7768_configure_dig_fil(struct iio_dev *dev,
> +				    enum ad7768_flt_type filter_type,
> +				    unsigned int dec_rate)
> +{
> +	struct ad7768_state *st = iio_priv(dev);
> +	int ret;
> +
> +	if (filter_type == SINC3) {
neat: switch (filter_type) { ?

> +		ret = ad7768_set_filter_type(dev, SINC3);
> +		if (ret)
> +			return ret;
> +
> +		/* recalculate the decimation for this filter mode */
> +		ret = ad7768_set_sinc3_dec_rate(st, dec_rate);
> +	} else if (filter_type == WIDEBAND) {
> +		ret = ad7768_set_filter_type(dev, filter_type);
> +		if (ret)
> +			return ret;
> +
> +		/* recalculate the decimation rate */
> +		ret = ad7768_set_dec_rate(st, dec_rate);
> +	} else {
> +		/* For SINC5 filter */
> +		/* Decimation 8 and 16 are set in the digital filter field */
> +		if (dec_rate <= 8) {
> +			ret = ad7768_set_filter_type(dev, SINC5_DEC_X8);
> +			if (ret)
> +				return ret;
> +
> +			st->dec_rate = 8;
> +		} else if (dec_rate <= 16) {
> +			ret = ad7768_set_filter_type(dev, SINC5_DEC_X16);
> +			if (ret)
> +				return ret;
> +
> +			st->dec_rate = 16;
> +		} else {
> +			ret = ad7768_set_filter_type(dev, SINC5);
> +			if (ret)
> +				return ret;
> +
> +			ret = ad7768_set_dec_rate(st, dec_rate);
> +		}
> +	}
> +
> +	/* Update scale table: scale values vary according to the precision */
> +	ad7768_fill_scale_tbl(dev);
> +
> +	return ret;
> +}
> +
...
> +static ssize_t decimation_rate_available_show(struct device *dev,
> +					      struct device_attribute *attr,
> +					      char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct ad7768_state *st = iio_priv(indio_dev);
> +	int len = 0;
> +
> +	/* Return decimation rate available in range format */
> +	buf[len++] = '[';
> +	if (st->filter_type == SINC3) {
switch (st->filter_type) { ?

> +		len += sysfs_emit_at(buf, len, "%d ", SINC3_DEC_RATE_MIN);
> +		len += sysfs_emit_at(buf, len, "%d ", SINC3_DEC_RATE_MIN);
> +		len += sysfs_emit_at(buf, len, "%d ", SINC3_DEC_RATE_MAX);
> +	} else if (st->filter_type == WIDEBAND) {
> +		len += sysfs_emit_at(buf, len, "%d ", WIDEBAND_DEC_RATE_MIN);
> +		len += sysfs_emit_at(buf, len, "%d ", WIDEBAND_DEC_RATE_MIN);
> +		len += sysfs_emit_at(buf, len, "%d ", WIDEBAND_DEC_RATE_MAX);
> +	} else {
> +		len += sysfs_emit_at(buf, len, "%d ", SINC5_DEC_RATE_MIN);
> +		len += sysfs_emit_at(buf, len, "%d ", SINC5_DEC_RATE_MIN);
> +		len += sysfs_emit_at(buf, len, "%d ", SINC5_DEC_RATE_MAX);
> +	}
> +
> +	buf[len - 1] = ']';
> +	buf[len++] = '\n';
> +
> +	return len;
> +}
> +