[PATCH v2] iio: adc: xilinx-xadc: Fix sequencer mode in postdisable for dual mux

[Erim, Salih]

[AMD Official Use Only - AMD Internal Distribution Only]

Hi Christofer,

The code change looks correct to me - it aligns postdisable with
preenable by reusing xadc_get_seq_mode(), and the scope is limited
to dual external mux configurations.

Since this is targeting stable, could you please share what hardware/board
this was tested on and how you verified that VAUX[8-15] channels
return correct data with the fix applied?

Reviewed-by: Salih Emin <salih.emin at amd.com>

Thanks,
Salih


> -----Original Message-----
> From: Simek, Michal <michal.simek at amd.com>
> Sent: Tuesday, March 10, 2026 7:43 AM
> To: Jonathan Cameron <jic23 at kernel.org>; Christofer Jonason
> <christofer.jonason at guidelinegeo.com>; Erim, Salih <Salih.Erim at amd.com>;
> O'Griofa, Conall <conall.ogriofa at amd.com>
> Cc: lars at metafoo.de; dlechner at baylibre.com; nuno.sa at analog.com;
> andy at kernel.org; victor.jonsson at guidelinegeo.com; linux-iio at vger.kernel.org;
> linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org;
> stable at vger.kernel.org
> Subject: Re: [PATCH v2] iio: adc: xilinx-xadc: Fix sequencer mode in postdisable
> for dual mux
>
> +Salih, Conall,
>
> On 3/7/26 13:41, Jonathan Cameron wrote:
> > On Wed,  4 Mar 2026 10:07:27 +0100
> > Christofer Jonason <christofer.jonason at guidelinegeo.com> wrote:
> >
> >> xadc_postdisable() unconditionally sets the sequencer to continuous
> >> mode. For dual external multiplexer configurations this is incorrect:
> >> simultaneous sampling mode is required so that ADC-A samples through
> >> the mux on VAUX[0-7] while ADC-B simultaneously samples through the
> >> mux on VAUX[8-15]. In continuous mode only ADC-A is active, so
> >> VAUX[8-15] channels return incorrect data.
> >>
> >> Since postdisable is also called from xadc_probe() to set the initial
> >> idle state, the wrong sequencer mode is active from the moment the
> >> driver loads.
> >>
> >> The preenable path already uses xadc_get_seq_mode() which returns
> >> SIMULTANEOUS for dual mux. Fix postdisable to do the same.
> >>
> >> Fixes: bdc8cda1d010 ("iio:adc: Add Xilinx XADC driver")
> >> Cc: stable at vger.kernel.org
> >> Signed-off-by: Christofer Jonason
> >> <christofer.jonason at guidelinegeo.com>
> >
> > I'll leave this on list for a little longer as I'd really like a
> > confirmation of this one from the AMD Xilinx folk.
>
> Salih/Conall: Please look at this patch and provide your comment or tag.
>
> Thanks,
> Michal