[PATCH v1 4/8] iio: dac: ds4424: reject -128 RAW value

[Oleksij Rempel]

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

With the previous check, userspace could pass -128, which gets converted
to a magnitude of 128 and then truncated by the 7-bit DAC field. This
ends up programming a zero magnitude with the sign bit set, i.e. an
unintended output (effectively 0 mA instead of -128 steps).

Reject -128 to avoid silently producing the wrong current.

Fixes: d632a2bd8ffc ("iio: dac: ds4422/ds4424 dac driver")
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx>
---
 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 072b7e6672cf..9c24c37d3c42 100644
--- a/drivers/iio/dac/ds4424.c
+++ b/drivers/iio/dac/ds4424.c
@@ -143,7 +143,7 @@ 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