linux-kernel - Re: [PATCH v11 11/11] iio: adc: ad7768-1: add low pass -3dB cutoff attribute

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Message-ID: <CAHp75VdbizxgF1U-LmEp-aTdWpZ5jAqvubk_7QH+RFLMrnRotQ@mail.gmail.com>
Date: Tue, 17 Jun 2025 23:17:32 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: aEwd4cS7j0Vvypg8@...le.fi.intel.com
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>, 
	Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-gpio@...r.kernel.org, andy@...nel.org, nuno.sa@...log.com, 
	Michael.Hennerich@...log.com, marcelo.schmitt@...log.com, jic23@...nel.org, 
	robh@...nel.org, krzk+dt@...nel.org, conor+dt@...nel.org, 
	marcelo.schmitt1@...il.com, linus.walleij@...aro.org, brgl@...ev.pl, 
	lgirdwood@...il.com, broonie@...nel.org, dlechner@...libre.com
Subject: Re: [PATCH v11 11/11] iio: adc: ad7768-1: add low pass -3dB cutoff attribute

On Tue, Jun 17, 2025 at 7:17 PM Jonathan Santos <jonath4nns@...il.com> wrote:
> On 06/13, Andy Shevchenko wrote:
> > On Wed, Jun 11, 2025 at 08:52:03AM -0300, Jonathan Santos wrote:
> > > Ad7768-1 has a different -3db frequency multiplier depending on
> > > the filter type configured. The cutoff frequency also varies according
> > > to the current ODR.
> > >
> > > Add a readonly low pass -3dB frequency cutoff attribute to clarify to
> > > the user which bandwidth is being allowed depending on the filter
> > > configurations.
> >
> > > +/* -3dB cutoff frequency multipliers (relative to ODR) for each filter type. */
> > > +static const int ad7768_filter_3db_odr_multiplier[] = {
> > > +   [AD7768_FILTER_SINC5] = 204,            /* 0.204 */
> > > +   [AD7768_FILTER_SINC3] = 262,            /* 0.2617 */
> > > +   [AD7768_FILTER_SINC3_REJ60] = 262,      /* 0.2617 */
> > > +   [AD7768_FILTER_WIDEBAND] = 433,         /* 0.433 */
> >
> > Just to be sure, is it 0.433 or 0.4333(3) actually? Sometimes datasheets have
> > rounding that even may lead to problems (see TSC issues for some of the Intel
> > CPUs in the past). That's behind my question.
>
> Every reference I have specifies it as 0.433, so I believe that is it.

Yeah, I see now. The base is 0.10825, which is multiplied by 4 in this case.

> > > +};

-- 
With Best Regards,
Andy Shevchenko