linux-kernel - [PATCH v1 6/8] iio: dac: ds4424: clear outputs on probe

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Message-ID: <20260119182424.1660601-7-o.rempel@pengutronix.de>
Date: Mon, 19 Jan 2026 19:24:22 +0100
From: Oleksij Rempel <o.rempel@...gutronix.de>
To: Jonathan Cameron <jic23@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>
Cc: Oleksij Rempel <o.rempel@...gutronix.de>,
	kernel@...gutronix.de,
	linux-kernel@...r.kernel.org,
	linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org,
	Andy Shevchenko <andy@...nel.org>,
	David Lechner <dlechner@...libre.com>,
	Nuno Sá <nuno.sa@...log.com>,
	David Jander <david@...tonic.nl>
Subject: [PATCH v1 6/8] iio: dac: ds4424: clear outputs on probe

The DS44xx devices have no reset pin or reset bit, so output registers
may retain preconfigured values across reboot or warm reset.

Also, the driver suspend/resume path restores from data->raw. When the
device is first probed, data->raw is zero-initialized and may not match
the actual hardware state. A later suspend/resume can therefore change an
output from a preconfigured non-zero value to 0 mA.

Initialize all channels to 0 output current during probe to ensure a
deterministic baseline and consistent suspend/resume behavior.

Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
 drivers/iio/dac/ds4424.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/iio/dac/ds4424.c b/drivers/iio/dac/ds4424.c
index a0c60eb89717..2d299a52cede 100644
--- a/drivers/iio/dac/ds4424.c
+++ b/drivers/iio/dac/ds4424.c
@@ -220,6 +220,20 @@ static int ds4424_verify_chip(struct iio_dev *indio_dev)
 	return ret;
 }
 
+static int ds4424_init(struct iio_dev *indio_dev)
+{
+	int i, ret;
+
+	/* Set all channels to 0 current. */
+	for (i = 0; i < indio_dev->num_channels; i++) {
+		ret = ds4424_set_value(indio_dev, 0, &indio_dev->channels[i]);
+		if (ret < 0)
+			return ret;
+	}
+
+	return 0;
+}
+
 static int ds4424_setup_channels(struct i2c_client *client,
 				 struct ds4424_data *data,
 				 struct iio_dev *indio_dev)
@@ -397,6 +411,11 @@ static int ds4424_probe(struct i2c_client *client)
 	if (ret)
 		goto fail;
 
+	/* No reset pin/bit: clear any preconfigured output on probe. */
+	ret = ds4424_init(indio_dev);
+	if (ret)
+		goto fail;
+
 	indio_dev->modes = INDIO_DIRECT_MODE;
 	indio_dev->info = &ds4424_iio_info;
 
-- 
2.47.3