On Mon, Feb 8, 2021 at 4:27 PM Wilfried Wessner
<wilfried.wessner@xxxxxxxxx> wrote:
>
> Fixes a wrong bit mask used for the ADC's result, which was caused by an
> improper usage of the GENMASK() macro. The bits higher than ADC's
> resolution are undefined and if not masked out correctly, a wrong result
> can be given. The GENMASK() macro indexing is zero based, so the mask has
> to go from [resolution - 1 , 0].
> Fixes: 7f40e0614317f ("iio:adc:ad7949: Add AD7949 ADC driver family")
>
Shouldn't be blank like here, but I think Jonathan can fix when applying.
Jonathan, can you also amend the subject (I totally forgot about
subsubsystem prefix)?
Should be like:
"iio: adc: ad7949: fix wrong results due to incorrect bit mask"
And FWIW,
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> Signed-off-by: Wilfried Wessner <wilfried.wessner@xxxxxxxxx>
>
> ---
>
> The issue was found in combination of an AD7682 ADC with an ARM based
> iMX7-CPU. The SPI line was analyzed with a logic analyzer and a
> discrepancy between applied voltage level and the ADC reported value
> in user space was observed. Digging into the driver code revealed an
> improper mask used for the ADC-result.
>
>
> drivers/iio/adc/ad7949.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/iio/adc/ad7949.c b/drivers/iio/adc/ad7949.c
> index 5d597e5050f6..1b4b3203e428 100644
> --- a/drivers/iio/adc/ad7949.c
> +++ b/drivers/iio/adc/ad7949.c
> @@ -91,7 +91,7 @@ static int ad7949_spi_read_channel(struct ad7949_adc_chip *ad7949_adc, int *val,
> int ret;
> int i;
> int bits_per_word = ad7949_adc->resolution;
> - int mask = GENMASK(ad7949_adc->resolution, 0);
> + int mask = GENMASK(ad7949_adc->resolution - 1, 0);
> struct spi_message msg;
> struct spi_transfer tx[] = {
> {
> --
> 2.25.1
>
--
With Best Regards,
Andy Shevchenko
