Re: [PATCH v2 1/3] iio: adc: ad7124: Fix 3dB filter frequency reading

[Marcelo Schmitt <marcelo.schmitt1@gmail.com>]

Hello,

On 03/17, 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).

Potentially dumb question but, how do we get to these factors between ODR and
3dB frequency?
Looking at Table 8, Table 18, Table 28, and 
dividing values from Output Data Rate (SPS) column by respective
values from f3dB (Hz) column gives me 4.3478.
If the zero latency mode SPS values are used as numerator, the result is 1.0869
for most pairs of SPS and f3dB.

> 
> 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 3ea81a98e455..7d5d84a07cae 100644
> --- a/drivers/iio/adc/ad7124.c
> +++ b/drivers/iio/adc/ad7124.c
> @@ -301,9 +301,9 @@ static int ad7124_get_3db_filter_freq(struct ad7124_state *st,
>  
>  	switch (st->channels[channel].cfg.filter_type) {
>  	case AD7124_SINC3_FILTER:
> -		return DIV_ROUND_CLOSEST(fadc * 230, 1000);
> +		return DIV_ROUND_CLOSEST(fadc * 272, 1000);
>  	case AD7124_SINC4_FILTER:
> -		return DIV_ROUND_CLOSEST(fadc * 262, 1000);
> +		return DIV_ROUND_CLOSEST(fadc * 230, 1000);
>  	default:
>  		return -EINVAL;
>  	}
> -- 
> 2.47.1
> 
>