linux-kernel - [PATCH v2 16/16] iio: adc: ad7768-1: add low pass -3dB cutoff attribute

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Message-ID: <91b697b66a42ead9e05dd4e79d6fb1e776c569d6.1737985435.git.Jonathan.Santos@analog.com>
Date: Mon, 27 Jan 2025 12:14:31 -0300
From: Jonathan Santos <Jonathan.Santos@...log.com>
To: <linux-iio@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC: Jonathan Santos <Jonathan.Santos@...log.com>, <lars@...afoo.de>,
        <Michael.Hennerich@...log.com>, <marcelo.schmitt@...log.com>,
        <jic23@...nel.org>, <robh@...nel.org>, <krzk+dt@...nel.org>,
        <conor+dt@...nel.org>, <jonath4nns@...il.com>,
        <marcelo.schmitt1@...il.com>
Subject: [PATCH v2 16/16] 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.

Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
---
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;
 	}
 
-- 
2.34.1