[PATCH v5 14/14] iio: adc: ad7768-1: add low pass -3dB cutoff attribute

Jonathan Santos
2025-04-11T15:59:51Z

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.

Reviewed-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
---
v5 Changes:
* None

v4 Changes:
* None

v3 Changes:
* None

v2 Changes:
* New patch in v2.
---
drivers/iio/adc/ad7768-1.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
index ab46714ee20a..d3d5b3505c41 100644
--- a/drivers/iio/adc/ad7768-1.c
+++ b/drivers/iio/adc/ad7768-1.c
@@ -152,6 +152,17 @@ 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[] = {
+ [AD7768_FILTER_SINC5] = 204,
+ [AD7768_FILTER_SINC3] = 262,
+ [AD7768_FILTER_SINC3_REJ60] = 262,
+ [AD7768_FILTER_WIDEBAND] = 433,
+};
+
static const int ad7768_mclk_div_rates[4] = {
16, 8, 4, 2,
};
@@ -230,7 +241,8 @@ static const struct iio_chan_spec ad7768_channels[] = {
.type = IIO_VOLTAGE,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
.info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) |
- BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
+ BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO) |
+ BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY),
.info_mask_shared_by_type_available = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),
.info_mask_shared_by_all_available = BIT(IIO_CHAN_INFO_SAMP_FREQ),
@@ -765,7 +777,7 @@ 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))
@@ -803,6 +815,12 @@ 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;
}

--
2.34.1