Re: [PATCH v2] iio: ti-ads7138: Disable STATS_EN bit while reading conversion results

[Paul Geurts]

> On Fri, Jun 19, 2026 at 09:42:08AM -0500, David Lechner wrote:
> > On 6/19/26 4:00 AM, Paul Geurts wrote:
> > > The device might update channel data while it's read by the host,
> > > providing a data race. Disable the update of the channel stats before
> > > reading the values.
> >
> > This description seems a bit short on details. It looks like this
> > driver doesn't support buffered reads. So if we disable statistics
> > during a direct read, why would we want to enable statistics in
> > the first place?
>
> I believe this patch is initiated by
> "Until a new conversion result is available, previous values can be read from
> the statistics registers. Before reading the statistics registers, set STATS_EN
> to 0 to prevent any updates to this register block."
> from the datasheet.
>
> I would rather like to know if this is IRL problem, or just a datasheet reading
> based code.

This is indeed the part of the datahseet I got the solution from. Our real life
scenario was that the register read from the RECENT register was constantly
flipping between values 0x24F0 and 0x2500. Due to the STATS_EN not being
cleared, we occasionally read 0x2400 and 0x25F0. So this is based on a real
life problem.

>
> > (This driver suffers from the comments say "what" rather than "why"
> > /* Enable statistics and digital window comparator */ so it is hard
> > to say what the original intention was.)
> >
> > Can you explain more what this race condition is about and what
> > happens before the fix vs. after the fix? People generally do this
> > with two columns showing concurrent function calls.
> >
> > It seems to me like disabling statistics would break IIO_CHAN_INFO_PEAK.

I think it indeed could break the PEAK value. But I think the data race is a
bigger issue. I'm not sure using the statistics at all is a good idea for
this device, but I'm also not sure there is another option. TBH, I don't
really have the time now to properly fix all of this. I just saw and
quickly fixed this, and thought it would be good to let you know this is
an issue.

>
> --
> With Best Regards,
> Andy Shevchenko

br,
Paul