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

[Nuno Sá]

On Wed, 2026-03-04 at 10:07 +0100, Christofer Jonason 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@xxxxxxxxxxxxxxx
> Signed-off-by: Christofer Jonason <christofer.jonason@xxxxxxxxxxxxxxxx>
> ---

>From a code standpoint:

Reviewed-by: Nuno Sá <nuno.sa@xxxxxxxxxx>

> Changes in v2:
>   - Align continuation line to opening parenthesis (Andy)
>  drivers/iio/adc/xilinx-xadc-core.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/xilinx-xadc-core.c b/drivers/iio/adc/xilinx-xadc-core.c
> index e257c1b94..3980dfacb 100644
> --- a/drivers/iio/adc/xilinx-xadc-core.c
> +++ b/drivers/iio/adc/xilinx-xadc-core.c
> @@ -817,6 +817,7 @@ static int xadc_postdisable(struct iio_dev *indio_dev)
>  {
>  	struct xadc *xadc = iio_priv(indio_dev);
>  	unsigned long scan_mask;
> +	int seq_mode;
>  	int ret;
>  	int i;
>  
> @@ -824,6 +825,12 @@ static int xadc_postdisable(struct iio_dev *indio_dev)
>  	for (i = 0; i < indio_dev->num_channels; i++)
>  		scan_mask |= BIT(indio_dev->channels[i].scan_index);
>  
> +	/*
> +	 * Use the correct sequencer mode for the idle state: simultaneous
> +	 * mode for dual external mux configurations, continuous otherwise.
> +	 */
> +	seq_mode = xadc_get_seq_mode(xadc, scan_mask);
> +
>  	/* Enable all channels and calibration */
>  	ret = xadc_write_adc_reg(xadc, XADC_REG_SEQ(0), scan_mask & 0xffff);
>  	if (ret)
> @@ -834,11 +841,11 @@ static int xadc_postdisable(struct iio_dev *indio_dev)
>  		return ret;
>  
>  	ret = xadc_update_adc_reg(xadc, XADC_REG_CONF1, XADC_CONF1_SEQ_MASK,
> -		XADC_CONF1_SEQ_CONTINUOUS);
> +				  seq_mode);
>  	if (ret)
>  		return ret;
>  
> -	return xadc_power_adc_b(xadc, XADC_CONF1_SEQ_CONTINUOUS);
> +	return xadc_power_adc_b(xadc, seq_mode);
>  }
>  
>  static int xadc_preenable(struct iio_dev *indio_dev)