linux-kernel - [PATCH v11 11/11] iio: adc: ad7768-1: add low pass -3dB cutoff attribute

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Message-ID: <804d66f1858014d7278aec3344d81c223661e878.1749569957.git.Jonathan.Santos@analog.com>
Date: Wed, 11 Jun 2025 08:52:03 -0300
From: Jonathan Santos <Jonathan.Santos@...log.com>
To: <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>
CC: Jonathan Santos <Jonathan.Santos@...log.com>, <andy@...nel.org>,
        <nuno.sa@...log.com>, <Michael.Hennerich@...log.com>,
        <marcelo.schmitt@...log.com>, <jic23@...nel.org>, <robh@...nel.org>,
        <krzk+dt@...nel.org>, <conor+dt@...nel.org>,
        <marcelo.schmitt1@...il.com>, <linus.walleij@...aro.org>,
        <brgl@...ev.pl>, <lgirdwood@...il.com>, <broonie@...nel.org>,
        <jonath4nns@...il.com>, <dlechner@...libre.com>
Subject: [PATCH v11 11/11] iio: adc: ad7768-1: add low pass -3dB cutoff attribute

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@...log.com>
Reviewed-by: David Lechner <dlechner@...libre.com>
Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
---
v11 Changes:
* Applied suggestions from Andy.

v10 Changes:
* None

v9 Changes:
* Rearranged new BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY) to
  make the diff look cleaner.

v8 Changes:
* None

v7 Changes:
* None

v6 Changes:
* None

v5 Changes:
* None

v4 Changes:
* None

v3 Changes:
* None

v2 Changes:
* New patch in v2.
---
 drivers/iio/adc/ad7768-1.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
index 291ed801a8a0..e4716e20fcdf 100644
--- a/drivers/iio/adc/ad7768-1.c
+++ b/drivers/iio/adc/ad7768-1.c
@@ -152,6 +152,14 @@ enum ad7768_scan_type {
 	AD7768_SCAN_TYPE_HIGH_SPEED,
 };
 
+/* -3dB cutoff frequency multipliers (relative to ODR) for each filter type. */
+static const int ad7768_filter_3db_odr_multiplier[] = {
+	[AD7768_FILTER_SINC5] = 204,		/* 0.204 */
+	[AD7768_FILTER_SINC3] = 262,		/* 0.2617 */
+	[AD7768_FILTER_SINC3_REJ60] = 262,	/* 0.2617 */
+	[AD7768_FILTER_WIDEBAND] = 433,		/* 0.433 */
+};
+
 static const int ad7768_mclk_div_rates[] = {
 	16, 8, 4, 2,
 };
@@ -746,6 +754,7 @@ 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_LOW_PASS_FILTER_3DB_FREQUENCY) |
 					    BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
 		.info_mask_shared_by_type_available = BIT(IIO_CHAN_INFO_OVERSAMPLING_RATIO),
 		.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_SAMP_FREQ),
@@ -766,7 +775,7 @@ 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))
@@ -804,6 +813,12 @@ 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