[PATCH v3 5/9] iio: adc: ti-ads1262: support input chopping

[Kurt Borja <kuurtb@gmail.com>]

Enable per-channel input chopping via the "input-chopping" property.
As the device withholds the first conversion in chop mode, single reads
are taken in CONTINUOUS run mode with a brief start/stop pulse, as
recommended by the datasheet (Section 9.4.1.2).

Signed-off-by: Kurt Borja <kuurtb@gmail.com>
---
 drivers/iio/adc/ti-ads1262.c | 27 ++++++++++++++++++++++-----
 1 file changed, 22 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/adc/ti-ads1262.c b/drivers/iio/adc/ti-ads1262.c
index 360ce01a5871..e2659941e1af 100644
--- a/drivers/iio/adc/ti-ads1262.c
+++ b/drivers/iio/adc/ti-ads1262.c
@@ -210,6 +210,7 @@ struct ads1262_channel {
 	u8 ref_n;
 	bool ref_reversal;
 	bool is_resistance;
+	bool input_chop;
 	int offset;
 	int scales[6][2];
 	size_t num_scales;
@@ -374,7 +375,7 @@ static int ads1262_dev_stop(struct ads1262 *st)
 	return ret;
 }
 
-static int ads1262_dev_start_one(struct ads1262 *st)
+static int ads1262_dev_start_one(struct ads1262 *st, u8 runmode)
 {
 	int ret;
 
@@ -382,7 +383,7 @@ static int ads1262_dev_start_one(struct ads1262 *st)
 	if (ret)
 		return ret;
 
-	if (st->start_gpiod) {
+	if (runmode == ADS1262_RUNMODE_CONTINUOUS || st->start_gpiod) {
 		/*
 		 * The START pulse timing requirement is 4 clock cycles, at the
 		 * minimum clock rate this is 4 microseconds.
@@ -431,8 +432,10 @@ static int ads1262_channel_enable(struct ads1262 *st,
 	guard(mutex)(&st->xfer_lock);
 	guard(mutex)(&st->chan_lock);
 
-	val = FIELD_PREP(ADS1262_MODE0_REFREV_MASK, chan->ref_reversal);
+	val = FIELD_PREP(ADS1262_MODE0_INPUT_CHOP_MASK, chan->input_chop) |
+	      FIELD_PREP(ADS1262_MODE0_REFREV_MASK, chan->ref_reversal);
 	ret = regmap_update_bits(st->regmap, ADS1262_MODE0_REG,
+				 ADS1262_MODE0_INPUT_CHOP_MASK |
 				 ADS1262_MODE0_REFREV_MASK, val);
 	if (ret)
 		return ret;
@@ -473,13 +476,26 @@ static int ads1262_channel_read(struct iio_dev *indio_dev,
 				const struct iio_chan_spec *spec, __be32 *val)
 {
 	struct ads1262 *st = iio_priv(indio_dev);
+	struct ads1262_channel *chan = &st->channels[spec->scan_index];
+	u8 runmode;
 	int ret;
 
 	IIO_DEV_ACQUIRE_DIRECT_MODE(indio_dev, claim);
 	if (IIO_DEV_ACQUIRE_FAILED(claim))
 		return -EBUSY;
 
-	ret = ads1262_set_runmode(st, ADS1262_RUNMODE_PULSE);
+	/*
+	 * When a channel has chop mode or IDAC rotation mode, the first
+	 * conversion is always withheld so the datasheet suggests using the
+	 * CONTINUOUS mode and briefly starting and stopping conversions to
+	 * achieve the same effect (Section 9.4.1.2).
+	 */
+	if (chan->input_chop)
+		runmode = ADS1262_RUNMODE_CONTINUOUS;
+	else
+		runmode = ADS1262_RUNMODE_PULSE;
+
+	ret = ads1262_set_runmode(st, runmode);
 	if (ret)
 		return ret;
 
@@ -489,7 +505,7 @@ static int ads1262_channel_read(struct iio_dev *indio_dev,
 
 	reinit_completion(&st->drdy);
 
-	ret = ads1262_dev_start_one(st);
+	ret = ads1262_dev_start_one(st, runmode);
 	if (ret)
 		return ret;
 
@@ -1134,6 +1150,7 @@ static int ads1262_parse_channel_node(struct ads1262 *st,
 		}
 	}
 
+	chan->input_chop = fwnode_property_read_bool(node, "input-chopping");
 	chan->ref_reversal = fwnode_property_read_bool(node, "ti,reference-reversal");
 
 	return 0;

-- 
2.55.0