iio: adc: ad7944: mask high bits on direct read

Apply a mask to the raw value received over the SPI bus for unsigned
direct reads. As we found recently, SPI controllers may not set unused
bits to 0 when reading with bits_per_word != {8,16,32}. The ad7944 uses
bits_per_word of 14 and 18, so we need to mask the value to be sure we
returning the correct value to userspace during a direct read.

Fixes: d1efcf8871db ("iio: adc: ad7944: add driver for AD7944/AD7985/AD7986")
Signed-off-by: David Lechner <dlechner@baylibre.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Link: https://patch.msgid.link/20250505-iio-adc-ad7944-max-high-bits-on-direct-read-v1-1-b173facceefe@baylibre.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/drivers/iio/adc/ad7944.c b/drivers/iio/adc/ad7944.c
index 2f949fe5587318957f2e423029294ced0a6f803d..37a137bd83571b055e970a8cd483d8726972d637 100644 (file)
--- a/drivers/iio/adc/ad7944.c
+++ b/drivers/iio/adc/ad7944.c
@@ -377,6 +377,8 @@ static int ad7944_single_conversion(struct ad7944_adc *adc,
 
        if (chan->scan_type.sign == 's')
                *val = sign_extend32(*val, chan->scan_type.realbits - 1);
+       else
+               *val &= GENMASK(chan->scan_type.realbits - 1, 0);
 
        return IIO_VAL_INT;
 }