Re: [PATCH v1 2/9] iio: inkern: error out on unsupported offset type

Liam Beguin
2021-05-31T14:25:25Z

Hi Peter,

On Mon May 31, 2021 at 5:45 AM EDT, Peter Rosin wrote:
> Hi!
>
> On 2021-05-30 02:59, Liam Beguin wrote:
> > From: Liam Beguin <lvb@xiphos.com>
> >
> > iio_convert_raw_to_processed_unlocked() assumes the offset is an
> > integer. Make that clear to the consumer by returning an error when an
> > unsupported offset type is detected.
> >
> > Signed-off-by: Liam Beguin <lvb@xiphos.com>
> > ---
> > drivers/iio/inkern.c | 6 +++++-
> > 1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> > index 4b6a8e11116a..dede4536d499 100644
> > --- a/drivers/iio/inkern.c
> > +++ b/drivers/iio/inkern.c
> > @@ -595,8 +595,12 @@ static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan,
> > int ret;
> >
> > ret = iio_channel_read(chan, &offset, NULL, IIO_CHAN_INFO_OFFSET);
> > - if (ret >= 0)
> > + if (ret == IIO_VAL_INT) {
> > raw64 += offset;
> > + } else if (ret >= 0) {
> > + dev_err(&chan->indio_dev->dev, "unsupported offset type");
> > + return -EINVAL;
> > + }
> >
> > scale_type = iio_channel_read(chan, &scale_val, &scale_val2,
> > IIO_CHAN_INFO_SCALE);
> >
>
> This breaks the implicit truncation that happens for drivers that have
> offsets of type IIO_VAL_INT_PLUS_{MICRO_DB,MICRO,NANO}
>
> Implicit truncation might be more appropriate than an error?
>
> However, to error out on fractional offsets etc still seem appropriate,
> but
> there are corner cases where the existing code did the right thing. E.g.
> a denominator of one or a fractional-log2 of zero, but a big denominator
> and
> a smaller numerator would also just result in a relatively harmless
> truncation.
>
> I don't know if it's really right to just break that?

Apologies for missing these. You're right that this change shouldn't
break what used to work implicitly. I'll rework this.

Liam

>
> Cheers,
> Peter