linux-kernel - Re: [PATCH v4 3/7] iio: frequency: adf41513: driver implementation

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Message-ID: <e5lcg5kkey3c6u2l4rlzzpolp7qkudhcofyzcx5s2tjbh2iwkg@js3fisv23zyj>
Date: Tue, 20 Jan 2026 10:43:28 +0000
From: Rodrigo Alencar <455.rodrigo.alencar@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...el.com>, 
	Rodrigo Alencar <455.rodrigo.alencar@...il.com>
Cc: rodrigo.alencar@...log.com, 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 v4 3/7] iio: frequency: adf41513: driver implementation

On 26/01/19 07:07PM, Andy Shevchenko wrote:
> On Mon, Jan 19, 2026 at 04:37:09PM +0000, Rodrigo Alencar wrote:
> > On 26/01/19 03:42PM, Andy Shevchenko wrote:
> > > On Mon, Jan 19, 2026 at 11:21:59AM +0000, Rodrigo Alencar wrote:
> > > > On 26/01/19 09:31AM, Andy Shevchenko wrote:
> > > > > On Fri, Jan 16, 2026 at 02:32:22PM +0000, Rodrigo Alencar via B4 Relay wrote:

...

> > > > > > +static int adf41513_parse_uhz(const char *str, u64 *freq_uhz)
> > > > > > +{
> > > > > > +	u64 uhz = 0;
> > > > > > +	int f_count = ADF41513_HZ_DECIMAL_PRECISION;
> > > > > > +	bool frac_part = false;
> > > > > > +
> > > > > > +	if (str[0] == '+')
> > > > > > +		str++;
> > > > > > +
> > > > > > +	while (*str && f_count > 0) {
> > > > > > +		if ('0' <= *str && *str <= '9') {
> > > > > > +			uhz = uhz * 10 + *str - '0';
> > > > > > +			if (frac_part)
> > > > > > +				f_count--;
> > > > > > +		} else if (*str == '\n') {
> > > > > > +			if (*(str + 1) == '\0')
> > > > > > +				break;
> > > > > > +			return -EINVAL;
> > > > > 
> > > > > > +		} else if (*str == '.' && !frac_part) {
> > > > > 
> > > > > This can be found by strchr() / strrchr() (depending on the expectations of
> > > > > the input).
> > > > > 
> > > > > > +			frac_part = true;
> > > > > > +		} else {
> > > > > > +			return -EINVAL;
> > > > > > +		}
> > > > > > +		str++;
> > > > > > +	}
> > > > > 
> > > > > With the above the rest becomes just a couple of simple_strtoull() calls with
> > > > > a couple of int_pow(10) calls (and some validation on top).
> > > > > 
> > > > > > +	for (; f_count > 0; f_count--)
> > > > > > +		uhz *= 10;
> > > > > 
> > > > > This is int_pow(10).
> > > > > 
> > > > > > +	*freq_uhz = uhz;
> > > > > > +
> > > > > > +	return 0;
> > > > > > +}
> > > > 
> > > > The current implementation is kind of a stripped version of
> > > > __iio_str_to_fixpoint(). Would you prefer something like this, then?:
> > > 
> > > Do they have most of the parts in common? If so, why can't we use
> > > __iio_str_to_fixpoint() directly? Or why can't we slightly refactor
> > > that to give us the results we need here?
> > 
> > __iio_str_to_fixpoint() only parses "int" chunks, adf41513_parse_uhz
> > was modified to accomodate the u64 parsing removing unnecessary stuff.
> 
> But why? The fractional part most likely will be kept int (it's up to 10⁻⁹).
> The integer can be bigger than 10⁹?
> 

Correct, integer part of the frequency value goes up to 26.5 GHz
(uint_max is approx 4.3 GHz). Also, with the dual modulus, the PLL can
achieve micro Hz resolution.

Kind regards,

Rodrigo Alencar