On Sat, Feb 6, 2021 at 6:01 PM Jonathan Cameron <jic23@xxxxxxxxxx> wrote:
>
> On Sat, 6 Feb 2021 15:52:58 +0100
> 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].
>
> Hi Wilfried,
>
> Welcome to IIO and kernel in general!
>
> It's useful to add to the description if the error was found by inspection / script
> or by observing an actual error on hardware?
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 the error.
>
> Also, needs a fixes tag so we can work out what kernels to back port it to.
Not sure about that, but I found the issue in:
commit 61556703b610a104de324e4f061dc6cf7b218b46 (HEAD -> master,
origin/master, origin/HEAD)
Merge: 3afe9076a7c1 7f3414226b58
Author: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Wed Feb 3 11:56:58 2021 -0800
Merge tag 'for-linus-5.11-rc7' of
git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml
>
> +CC Charle-Antoine Couret as the original driver author.
done.
I wrote also an email to Charles-Antoine with the proposed fix, his comment was:
------
[Wilfried:]
>> since the GENMASK macro uses zero-based indexing?
>>
[Charles-Antoine:]
>You're right, it's a mistake.
>It wouldn't be a problem in many cases but it's better to be compliant.
[Wilfried:]
>> Could you pls. comment on that?
>>
[Charles-Antoine:]
>Good for me.
------
>
> Thanks,
>
> Jonathan
>
> >
> > Signed-off-by: Wilfried Wessner <wilfried.wessner@xxxxxxxxx>
> >
> > ---
> > 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[] = {
> > {
>
