Re: [PATCH] iio: adc: max1363: sign-extend bipolar differential channel reads

[Jonathan Cameron <jic23@kernel.org>]

On Mon, 10 Aug 2026 23:50:53 +0700
Nguyễn Công <congnt264@gmail.com> wrote:

> On Mon, Aug 10, 2026 at 1:45 PM Andy Shevchenko
> <andy.shevchenko@gmail.com> wrote:
> >
> > On Mon, Aug 10, 2026 at 9:42 AM Cong Nguyen <congnt264@gmail.com> wrote:  
> > >
> > > The MAX1363 differential channels are bipolar (scan_type.sign = 's') and
> > > the device returns those samples in two's complement. However
> > > max1363_read_single_chan() masks the raw value to the ADC resolution and
> > > stores it as-is, without sign extension. A negative differential reading
> > > is therefore reported to userspace as a large positive value (for a 12-bit
> > > part, -1 reads back as 4095).  
> >
> > Try to make it more compact (remove unneeded or duplicative details,
> > do not blindly rely on AI).  
> 
> Done in v2 - trimmed both paragraphs down to the bug, one example, and
> the fix.
> 
> >  
> > > These channels expose only IIO_CHAN_INFO_RAW (no offset), so the raw sysfs
> > > value is expected to be the signed result. Sign-extend the masked value
> > > from the resolution bit for differential channels before returning it.
> > > Single-ended channels are unipolar (sign = 'u') and are left unchanged.  
> >
> > Same here.
> >  
> > > Fixes: 168c9d95a940 ("iio:adc:max1363 move from staging.")  
> >
> > This is a wrong reference in case the driver existed before (and that
> > is suggested by the commit description).
> >
> > --
> > With Best Regards,
> > Andy Shevchenko  
> 
> Right, the bug predates the move. The driver was added in 2010 by
> d1325cf45077 ("Staging: IIO: max1363 ADC driver"), which already reads
> differential channels with an unsigned mask, so v2 uses that as the
> Fixes: tag.

Trivial thing to watch out for - don't put anything a thread that
smells like a tag.  b4 tends to scrape them and if I'm not paying
attention (or like in this case my git hooks catch it) we end up
with bonus tags.


> Thanks for the review.
> Cong