On Wed, 30 Oct 2024 15:16:11 +0200
Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> The KX022A provides the accelerometer data in two subsequent registers.
> The registers are laid out so that the value obtained via bulk-read of
> these registers can be interpreted as signed 16-bit little endian value.
> The read value is converted to cpu_endianes and stored into 32bit integer.
> The le16_to_cpu() casts value to unsigned 16-bit value, and when this is
> assigned to 32-bit integer the resulting value will always be positive.
>
> This has not been a problem to users (at least not all users) of the sysfs
> interface, who know the data format based on the scan info and who have
> converted the read value back to 16-bit signed value.
They shouldn't be doing that. Scaninfo is for buffered values only
This should indeed be signed.
>
> This, however, will be a problem for those who use the in-kernel
> interfaces, especially the iio_read_channel_processed_scale().
>
> The iio_read_channel_processed_scale() performs multiplications to the
> returned (always positive) raw value, which will cause strange results
> when the data from the sensor has been negative.
>
> Fix the read_raw format by casting the result of the le_to_cpu() to
> signed 16-bit value before assigning it to the integer. This will make
> the negative readings to be correctly reported as negative.
>
> This fix will be visible to users by changing values returned via sysfs
> to appear in correct (negative) format.
>
> Reported-by: Kalle Niemi <kaleposti@xxxxxxxxx>
> Fixes: 7c1d1677b322 ("iio: accel: Support Kionix/ROHM KX022A accelerometer")
> Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>
> Tested-by: Kalle Niemi <kaleposti@xxxxxxxxx>
> ---
> drivers/iio/accel/kionix-kx022a.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/iio/accel/kionix-kx022a.c b/drivers/iio/accel/kionix-kx022a.c
> index 53d59a04ae15..b6a828a6df93 100644
> --- a/drivers/iio/accel/kionix-kx022a.c
> +++ b/drivers/iio/accel/kionix-kx022a.c
> @@ -594,7 +594,7 @@ static int kx022a_get_axis(struct kx022a_data *data,
> if (ret)
> return ret;
>
> - *val = le16_to_cpu(data->buffer[0]);
> + *val = (s16)le16_to_cpu(data->buffer[0]);
LGTM.
>
> return IIO_VAL_INT;
> }
>
> base-commit: 81983758430957d9a5cb3333fe324fd70cf63e7e
