linux-kernel - [PATCH v5 01/13] iio: dac: ds4424: reject -128 RAW value

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Message-ID: <20260204140045.390677-2-o.rempel@pengutronix.de>
Date: Wed,  4 Feb 2026 15:00:33 +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>,
	stable@...r.kernel.org,
	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 v5 01/13] iio: dac: ds4424: reject -128 RAW value

The DS442x DAC uses sign-magnitude encoding, so -128 cannot be represented
in hardware (7-bit magnitude).

Previously, passing -128 resulted in a truncated value that programmed
0mA (magnitude 0) instead of the expected maximum negative current,
effectively failing silently.

Reject -128 to avoid producing the wrong current.

Fixes: d632a2bd8ffc ("iio: dac: ds4422/ds4424 dac driver")
Cc: <stable@...r.kernel.org>
Signed-off-by: Oleksij Rempel <o.rempel@...gutronix.de>
---
changes v5:
- no changes
changes v4:
- Restore v1 implementation: Keep this patch as a minimal fix suitable
  for stable backports
- Move the refactoring (bitwise operations and GENMASK usage) to a
  separate follow-up patch.
changes v3:
- (Merged into refactoring patch in v3, now split again)
---
 drivers/iio/dac/ds4424.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iio/dac/ds4424.c b/drivers/iio/dac/ds4424.c
index a8198ba4f98a..059acca45f64 100644
--- a/drivers/iio/dac/ds4424.c
+++ b/drivers/iio/dac/ds4424.c
@@ -141,7 +141,7 @@ static int ds4424_write_raw(struct iio_dev *indio_dev,
 
 	switch (mask) {
 	case IIO_CHAN_INFO_RAW:
-		if (val < S8_MIN || val > S8_MAX)
+		if (val <= S8_MIN || val > S8_MAX)
 			return -EINVAL;
 
 		if (val > 0) {
-- 
2.47.3