Re: [PATCH 3/3] iio: adc: ad7124: Disable all channels at probe time

[Jonathan Cameron <jic23@kernel.org>]

On Thu, 24 Oct 2024 19:17:05 +0200
Uwe Kleine-König <u.kleine-koenig@baylibre.com> wrote:

> When during a measurement two channels are enabled, two measurements are
> done that are reported sequencially in the DATA register. As the code
> triggered by reading one of the sysfs properties expects that only one
> channel is enabled it only reads the first data set which might or might
> not belong to the intended channel.
> 
> To prevent this situation disable all channels during probe. This fixes
> a problem in practise because the reset default for channel 0 is
> enabled. So all measurements before the first measurement on channel 0
> (which disables channel 0 at the end) might report wrong values.
> 
> Fixes: 7b8d045e497a ("iio: adc: ad7124: allow more than 8 channels")
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
Makes sense in general, but one comment inline.

> ---
>  drivers/iio/adc/ad7124.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iio/adc/ad7124.c b/drivers/iio/adc/ad7124.c
> index a5d91933f505..912ba6592560 100644
> --- a/drivers/iio/adc/ad7124.c
> +++ b/drivers/iio/adc/ad7124.c
> @@ -917,6 +917,9 @@ static int ad7124_setup(struct ad7124_state *st)
>  		 * set all channels to this default value.
>  		 */
>  		ad7124_set_channel_odr(st, i, 10);
> +
> +		/* Disable all channels to prevent unintended conversions. */
> +		ad_sd_write_reg(&st->sd, AD7124_CHANNEL(i), 2, 0x0001);
Why 1?  Build that default up from the register definitions rather than a magic
constant.


>  	}
>  
>  	ret = ad_sd_write_reg(&st->sd, AD7124_ADC_CONTROL, 2, st->adc_control);