linux-kernel - Re: [PATCH v2 5/6] iio: adc: ad7124: add filter support

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Message-ID: <CAHp75Vf69X4PmGx2c_9KvQwu1opLDyfL0+TyjwX2wTG9bgtMZw@mail.gmail.com>
Date: Fri, 12 Sep 2025 07:49:59 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: David Lechner <dlechner@...libre.com>
Cc: Michael Hennerich <Michael.Hennerich@...log.com>, Jonathan Cameron <jic23@...nel.org>, 
	Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] iio: adc: ad7124: add filter support

On Fri, Sep 12, 2025 at 12:43 AM David Lechner <dlechner@...libre.com> wrote:
>
> Add support to the ad7124 driver for selecting the filter type.
>
> The filter type has an influence on the effective sampling frequency of
> each channel. For sinc3+pf{1,2,3,4}, the sampling frequency is fixed.
> For sinc{3,4} (without post filter), there is a factor of 3 or 4
> depending on the filter type. For the extra +sinc1, there is an extra
> averaging factor that depends on the power mode.
>
> In order to select the closest sampling frequency for each filter type,
> we keep a copy of the requested sampling frequency. This way, if the
> user sets the sampling frequency first and then selects the filter type,
> the sampling frequency will still be as close as possible to the
> requested value.
>
> Since we always either have the SINGLE_CYCLE bit set or have more than
> one channel enabled, the sampling frequency is always using the
> "zero-latency" calculation from the data sheet. This is only documented
> for the basic sinc{3,4} filters, so the other filter types had to be
> inferred and confirmed through testing.
>
> Since the flat filter type list consists of multiple register fields,
> the struct ad7124_channel_config::filter_type field is changed to the
> enum ad7124_filter_type type to avoid nested switch statements in a
> lot of places.

...

> -       factor = 32 * 4; /* N = 4 for default sinc4 filter. */
> -       odr_sel_bits = DIV_ROUND_CLOSEST(fclk, odr * factor +
> -                                              odr_micro * factor / MICRO);
> -       odr_sel_bits = clamp(odr_sel_bits, 1, 2047);
> +       divisor = cfg->requested_odr * factor +
> +                 cfg->requested_odr_micro * factor / MICRO;
> +       odr_sel_bits = clamp(DIV_ROUND_CLOSEST(fclk, divisor), 1, 2047);

I have a déjà vu feeling here. Is this similar code to elsewhere?  Can
it be factored out to a helper?


-- 
With Best Regards,
Andy Shevchenko