linux-kernel - Re: [PATCH v3 4/6] iio: frequency: adf41513: features on frequency change

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Message-ID: <ptyn5x7qkmbakkompmijo6xeego2xrhjoeyomkgrytwgwcsaid@heiq3ilnx5ky>
Date: Mon, 12 Jan 2026 09:45:49 +0000
From: Rodrigo Alencar <455.rodrigo.alencar@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>, 
	rodrigo.alencar@...log.com
Cc: linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org, Jonathan Cameron <jic23@...nel.org>, 
	David Lechner <dlechner@...libre.com>, Andy Shevchenko <andy@...nel.org>, 
	Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, 
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH v3 4/6] iio: frequency: adf41513: features on frequency
 change

On 26/01/09 09:07PM, Andy Shevchenko wrote:
> On Thu, Jan 08, 2026 at 12:14:53PM +0000, Rodrigo Alencar via B4 Relay wrote:
> 
> > Set Bleed current when PFD frequency changes (bleed enabled when in
> > fractional mode). Set lock detector window size, handling bias and
> > precision. Add phase resync support, setting clock dividers when
> > PFD frequency changes.
> 
> ...
> 
> > +static const u16 adf41513_ld_window_p1ns[] = {
> > +	9, 12, 16, 17, 21, 28, 29, 35,			/* 0 - 7 */
> > +	43, 47, 49, 52, 70, 79, 115			/* 8 - 14 */
> 
> Leave trailing comma.
> 
> > +};
> > +
> > +static const u8 adf41513_ldp_bias[] = {
> > +	0xC, 0xD, 0xE, 0x8, 0x9, 0x4, 0xA, 0x5,		/* 0 - 7 */
> > +	0x0, 0x6, 0xB, 0x1, 0x2, 0x7, 0x3		/* 8 - 14 */
> 
> Ditto.
> 
> > +};
> > +
> >  static const char * const adf41513_power_supplies[] = {
> >  	"avdd1", "avdd2", "avdd3", "avdd4", "avdd5", "vp"
> 
> Ditto.
> 
> >  };
> 
> ...
> 
> > +	bleed_value = div64_u64(st->settings.pfd_frequency_uhz * bleed_value,
> > +				1600ULL * HZ_PER_MHZ * MICROHZ_PER_HZ);
> 
> > +	u16 ld_window_p1ns = div64_u64(10ULL * NANO * MICROHZ_PER_HZ,
> > +				       st->settings.pfd_frequency_uhz << 1);
> 
> These multiplications (here and elsewhere) are (very) confusing.
> 
> I believe you want to have a frequency in Hz in µHz resolution. The second one
> can be close to this if used GIGA instead of NANO. But I think the better way
> to have something like the first one but with MICRO instead of MICROHZ_PER_HZ.
> 
> Please, put an order in these.

The first one: the numerator is in µHz, so the denominator is also in µHz so to
cancel the units.

The second one: window size is nanoseconds with 0.1 precision in the datasheet.
The numerator contains  MICROHZ_PER_HZ to convert µHz -> Hz = 1/s, and then
10ULL * NANO to convert 1/s into 0.1 ns.

How is that confusing? I am not sure GIGA is the right choice, as NANO shows
that I am targeting nanoseconds, no? 

> ...
> 
> > +	/* assuming both clock dividers hold similar values */
> > +	total_div = mul_u64_u64_div_u64(st->settings.pfd_frequency_uhz,
> > +					st->data.phase_resync_period_ns,
> > +					1ULL * MICRO * NANO);
> 
> This sounds good as we multiply Hz by ns.
> 

the numerator has a time in nanoseconds, so NANO 'cancels' that, as MICRO 'cancels'
the micro under µHz.

> ...
> 
> > +	st->data.phase_resync_period_ns = 0;
> 
> Do we even need this?
>

true, will adjust.

> > +	ret = device_property_read_u32(dev, "adi,phase-resync-period-ns", &tmp);
> > +	if (!ret)
> > +		st->data.phase_resync_period_ns = tmp;
> 
> Is the _period_ns of type u32? Then simply
> 
> 	device_property_read_u32(dev, "adi,phase-resync-period-ns", &st->data.phase_resync_period_ns);
> 
> -- 
> With Best Regards,
> Andy Shevchenko
> 

kind regards,

Rodrigo Alencar