iio: adc: ad7768-1: Fix conversion result sign

[ Upstream commit 8236644f5ecb180e80ad92d691c22bc509b747bb ]

The ad7768-1 ADC output code is two's complement, meaning that the voltage
conversion result is a signed value.. Since the value is a 24 bit one,
stored in a 32 bit variable, the sign should be extended in order to get
the correct representation.

Also the channel description has been updated to signed representation,
to match the ADC specifications.

Fixes: a5f8c7da3dbe ("iio: adc: Add AD7768-1 ADC basic support")
Reviewed-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Marcelo Schmitt <marcelo.schmitt@analog.com>
Signed-off-by: Sergiu Cuciurean <sergiu.cuciurean@analog.com>
Signed-off-by: Jonathan Santos <Jonathan.Santos@analog.com>
Cc: <Stable@vger.kernel.org>
Link: https://patch.msgid.link/505994d3b71c2aa38ba714d909a68e021f12124c.1741268122.git.Jonathan.Santos@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
index 9b9956c0b076fcd99553ab002c9318ed9224364e..c1adb95f2a4648a2ff287deffd67dee76bb2499c 100644 (file)
--- a/drivers/iio/adc/ad7768-1.c
+++ b/drivers/iio/adc/ad7768-1.c
@@ -142,7 +142,7 @@ static const struct iio_chan_spec ad7768_channels[] = {
                .channel = 0,
                .scan_index = 0,
                .scan_type = {
-                       .sign = 'u',
+                       .sign = 's',
                        .realbits = 24,
                        .storagebits = 32,
                        .shift = 8,
@@ -373,7 +373,7 @@ static int ad7768_read_raw(struct iio_dev *indio_dev,
                iio_device_release_direct_mode(indio_dev);
                if (ret < 0)
                        return ret;
-               *val = ret;
+               *val = sign_extend32(ret, chan->scan_type.realbits - 1);
 
                return IIO_VAL_INT;