Document that a zero output value is encoded with a don't-care sign bit
and that the driver verifies device presence via a readable register
since the hardware provides no device ID.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
---
 drivers/iio/dac/ds4424.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/iio/dac/ds4424.c b/drivers/iio/dac/ds4424.c
index 13acb427d43b..2ccac674878e 100644
--- a/drivers/iio/dac/ds4424.c
+++ b/drivers/iio/dac/ds4424.c
@@ -194,6 +194,7 @@ static int ds4424_write_raw(struct iio_dev *indio_dev,
 		if (val < -max_val || val > max_val)
 			return -EINVAL;
 
+		/* Canonicalize 0 to sink; datasheet treats sign as don't-care. */
 		if (val > 0) {
 			raw.source_bit = DS4424_SOURCE_I;
 			raw.dx = val;
@@ -213,6 +214,7 @@ static int ds4424_verify_chip(struct iio_dev *indio_dev)
 {
 	int ret, val;
 
+	/* No device ID; verify presence by a readable register. */
 	ret = ds4424_get_value(indio_dev, &val, 0);
 	if (ret < 0)
 		dev_err(&indio_dev->dev,
-- 
2.47.3