On 1/27/25 9:14 AM, Jonathan Santos wrote:
> Ad7768-1 has a different -3db frequency multiplier depending on
> the filter type configured. The cutoff frequency also varies according
> to the current ODR.
>
> Add a readonly low pass -3dB frequency cutoff attribute to clarify to
> the user which bandwidth is being allowed depending on the filter
> configurations.
>
> Signed-off-by: Jonathan Santos <Jonathan.Santos@xxxxxxxxxx>
> ---
> v2 Changes:
> * New patch in v2.
> ---
> drivers/iio/adc/ad7768-1.c | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> index 6d0b430a8d54..daf91ef6f77b 100644
> --- a/drivers/iio/adc/ad7768-1.c
> +++ b/drivers/iio/adc/ad7768-1.c
> @@ -149,6 +149,18 @@ enum ad7768_scan_type {
> AD7768_SCAN_TYPE_HIGH_SPEED,
> };
>
> +/*
> + * -3dB cutoff frequency multipliers (relative to ODR) for
> + * each filter type. Values are multiplied by 1000.
> + */
> +static const int ad7768_filter_3db_odr_multiplier[] = {
> + [SINC5] = 204,
> + [SINC5_DEC_X8] = 204,
> + [SINC5_DEC_X16] = 204,
> + [SINC3] = 261,
> + [WIDEBAND] = 433,
> +};
> +
> static const int ad7768_mclk_div_rates[4] = {
> 16, 8, 4, 2,
> };
> @@ -202,7 +214,8 @@ static const struct iio_chan_spec ad7768_channels[] = {
> .info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE),
> .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ) |
> - BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
> + BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |
> + BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY),
> .ext_info = ad7768_ext_info,
> .indexed = 1,
> .channel = 0,
> @@ -802,7 +815,7 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
> {
> struct ad7768_state *st = iio_priv(indio_dev);
> const struct iio_scan_type *scan_type;
> - int scale_uv, ret;
> + int scale_uv, ret, temp;
>
> scan_type = iio_get_current_scan_type(indio_dev, chan);
> if (IS_ERR(scan_type))
> @@ -842,6 +855,12 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
> case IIO_CHAN_INFO_OVERSAMPLING_RATIO:
> *val = st->oversampling_ratio;
>
> + return IIO_VAL_INT;
> +
> + case IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY:
> + temp = st->samp_freq * ad7768_filter_3db_odr_multiplier[st->filter_type];
> + *val = DIV_ROUND_CLOSEST(temp, 1000);
> +
> return IIO_VAL_INT;
> }
>
If this is read-only, do we actually need it? It looks like the attribute is
going to return 1 of 3 values that exactly matches the filter_type attribute,
so this is not really giving any additional info.
