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

[Christofer Jonason <christofer.jonason@guidelinegeo.com>]

Hi Salih,

Thanks for the review.

Tested on a custom Zynq-7030 board with two TMUX1308APWR analog
multiplexers in dual external mux configuration. The XADC is
instantiated as an AXI XADC Wizard IP with xlnx,external-mux
set to "dual" and xlnx,external-mux-channel set to 1.

Verified by reading all 16 external mux channels via sysfs
(in_voltageN_raw) and comparing against known reference voltages
on the board. Before the fix, channels routed through ADC-B
returned incorrect values. After the fix, all channels return
the expected voltages matching the board schematic.

Thanks,
Christofer
________________________________________
From: Erim, Salih <Salih.Erim@amd.com>
Sent: Wednesday, April 1, 2026 3:11 PM
To: Simek, Michal <michal.simek@amd.com>; Jonathan Cameron <jic23@kernel.org>; Christofer Jonason <christofer.jonason@guidelinegeo.com>; O'Griofa, Conall <conall.ogriofa@amd.com>
Cc: lars@metafoo.de <lars@metafoo.de>; dlechner@baylibre.com <dlechner@baylibre.com>; nuno.sa@analog.com <nuno.sa@analog.com>; andy@kernel.org <andy@kernel.org>; Victor Jonsson <victor.jonsson@guidelinegeo.com>; linux-iio@vger.kernel.org <linux-iio@vger.kernel.org>; linux-arm-kernel@lists.infradead.org <linux-arm-kernel@lists.infradead.org>; linux-kernel@vger.kernel.org <linux-kernel@vger.kernel.org>; stable@vger.kernel.org <stable@vger.kernel.org>
Subject: RE: [PATCH v2] iio: adc: xilinx-xadc: Fix sequencer mode in postdisable for dual mux
 
[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@amd.com>

Thanks,
Salih


> -----Original Message-----
> From: Simek, Michal <michal.simek@amd.com>
> Sent: Tuesday, March 10, 2026 7:43 AM
> To: Jonathan Cameron <jic23@kernel.org>; Christofer Jonason
> <christofer.jonason@guidelinegeo.com>; Erim, Salih <Salih.Erim@amd.com>;
> O'Griofa, Conall <conall.ogriofa@amd.com>
> Cc: lars@metafoo.de; dlechner@baylibre.com; nuno.sa@analog.com;
> andy@kernel.org; victor.jonsson@guidelinegeo.com; linux-iio@vger.kernel.org;
> linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> stable@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@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@vger.kernel.org
> >> Signed-off-by: Christofer Jonason
> >> <christofer.jonason@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