[PATCH v6 12/17] iio: adc: ad7768: Wait for digital filters to settle

[Janani Sunil <janani.sunil@analog.com>]

After synchronizing the channel mode configuration, wait for the longest
settling period required by the active profiles. Derive the delay from
the selected output data rate and the datasheet filter-settling limits.

Signed-off-by: Janani Sunil <janani.sunil@analog.com>
---
 drivers/iio/adc/ad7768.c | 38 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/drivers/iio/adc/ad7768.c b/drivers/iio/adc/ad7768.c
index ac236e5c74c7..f2c762688fb3 100644
--- a/drivers/iio/adc/ad7768.c
+++ b/drivers/iio/adc/ad7768.c
@@ -107,6 +107,8 @@
 #define AD7768_MAX_FREQ_PER_MODE			6
 #define AD7768_MAX_CHANNEL				8
 #define AD7768_NUM_CHANNEL_MODES			2
+#define AD7768_WIDEBAND_SETTLING_SAMPLES		68
+#define AD7768_SINC5_SETTLING_SAMPLES			7
 
 enum ad7768_filter_type {
 	AD7768_FILTER_TYPE_WIDEBAND,
@@ -596,6 +598,33 @@ static int ad7768_find_matching_mode(const bool *mode_used,
 	return -EINVAL;
 }
 
+static void ad7768_filter_wait(const unsigned int *mode_freq,
+			       const enum ad7768_filter_type *mode_filter,
+			       const bool *mode_used)
+{
+	unsigned int t_settle_us = 0;
+
+	for (unsigned int mode = 0; mode < AD7768_NUM_CHANNEL_MODES; mode++) {
+		unsigned int t_mode_us;
+		u8 settling_samples;
+
+		if (!mode_used[mode] || !mode_freq[mode])
+			continue;
+
+		if (mode_filter[mode] == AD7768_FILTER_TYPE_SINC5)
+			settling_samples = AD7768_SINC5_SETTLING_SAMPLES;
+		else
+			settling_samples = AD7768_WIDEBAND_SETTLING_SAMPLES;
+
+		t_mode_us = DIV_ROUND_UP(settling_samples * USEC_PER_SEC,
+					 mode_freq[mode]);
+		t_settle_us = max(t_settle_us, t_mode_us);
+	}
+
+	if (t_settle_us)
+		fsleep(t_settle_us);
+}
+
 static int ad7768_apply_channel_modes(struct iio_dev *indio_dev,
 				      const unsigned long *scan_mask)
 {
@@ -679,7 +708,14 @@ static int ad7768_apply_channel_modes(struct iio_dev *indio_dev,
 	if (ret)
 		return ret;
 
-	return ad7768_sync(st);
+	ret = ad7768_sync(st);
+	if (ret)
+		return ret;
+
+	/* Apply a filter settling time (datasheet Tables 28 and 29). */
+	ad7768_filter_wait(mode_freq, mode_filter, mode_used);
+
+	return 0;
 }
 
 static int ad7768_update_scan_mode(struct iio_dev *indio_dev,

-- 
2.43.0