Re: [PATCH 2/2] iio: adc: ad7124: Fix 3dB filter frequency reading

["Nuno Sá" <noname.nuno@gmail.com>]

On Wed, 2025-03-12 at 19:38 +0100, Uwe Kleine-König wrote:
> The sinc4 filter has a factor 0.23 between Output Data Rate and f_{3dB}
> and for sinc3 the factor is 0.272 according to the data sheets for
> ad7124-4 (Rev. E.) and ad7124-8 (Rev. F).
> 
> Fixes: cef2760954cf ("iio: adc: ad7124: add 3db filter")
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
> ---
>  drivers/iio/adc/ad7124.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7124.c b/drivers/iio/adc/ad7124.c
> index 67d49e6184f7..a3cb47ca3901 100644
> --- a/drivers/iio/adc/ad7124.c
> +++ b/drivers/iio/adc/ad7124.c
> @@ -291,9 +291,9 @@ static int ad7124_get_3db_filter_freq(struct ad7124_state *st,
>  
>  	switch (st->channels[channel].cfg.filter_type) {
>  	case AD7124_FILTER_FILTER_SINC3:
> -		return DIV_ROUND_CLOSEST(fadc * 230, 1000);
> -	case AD7124_FILTER_FILTER_SINC4:
>  		return DIV_ROUND_CLOSEST(fadc * 262, 1000);

I wonder if we shouldn't fix the sinc3 factor as well? Or at the very least mention
in the commit message why we're not doing it now. Otherwise it's confusing and raises
questions to state the proper factor in the commit and then look at this diff.

- Nuno Sá

> +	case AD7124_FILTER_FILTER_SINC4:
> +		return DIV_ROUND_CLOSEST(fadc * 230, 1000);
>  	default:
>  		return -EINVAL;
>  	}