linux-kernel - Re: [PATCH v7 2/2] iio: adc: Add ti-ads1018 driver

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Message-ID: <CAHp75VeuA-Wvs9o9cXBFxL6D90mvN9eQA=tOtxB2GT7sPSqw9w@mail.gmail.com>
Date: Wed, 10 Dec 2025 13:13:08 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Kurt Borja <kuurtb@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Tobias Sperling <tobias.sperling@...ting.com>, David Lechner <dlechner@...libre.com>, 
	Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v7 2/2] iio: adc: Add ti-ads1018 driver

On Wed, Dec 10, 2025 at 6:07 AM Kurt Borja <kuurtb@...il.com> wrote:
> On Mon Dec 8, 2025 at 3:19 PM -05, Andy Shevchenko wrote:

...

> >> +       /* ...Then calculate time per sample in microseconds. */
> >> +       return DIV_ROUND_UP(MICROHZ_PER_HZ, hz);
> >
> > If time per sample is in µs, the associated frequency is in MHz, so
> > the correct constant is HZ_PER_MHZ. What did I miss here?
>
> I was very confused about this, but the dimensional analysis works with
> HZ_PER_MHZ so it should be the right constant. Thanks!

You need to keep in mind the sign of the order of magnitude. Since we
don't use floats in the kernel, the small units are represented as
divisors in opposite to multipliers. So, the used one is 10⁻⁶, while
the proposed one is 10⁶.

...

> Do you have a suggestion for this? I can keep the ADS1018_FSR_TO_SCALE()
> macro but it will get a bit more complex or I can just hard code the
> scales and document the calculation. I'm inclined to do the latter.

I believe we will see based on your next version. Just avoid hard
coding magic numbers, and put more comments, ideally with the
references to a datasheet section.

-- 
With Best Regards,
Andy Shevchenko