On Mon, Feb 8, 2021 at 5:06 PM Andy Shevchenko
<andy.shevchenko@xxxxxxxxx> wrote:
>
> 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"
Should I send a v4 with the changes proposed by Andy?
It would change the subject.
And if so, should I add the tags:
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Reviewed-by: Charles-Antoine Couret <charles-antoine.couret@xxxxxxxxxxxxx>
Please advise, thank you!
Best Regards,
Willi
>
> 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
