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

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Message-ID: <hgy3bcrqqsvt7pobhnzuvwzhb2taetpxltkaxpigmmlvmlirod@v6anhmrsvv2r>
Date: Mon, 19 Jan 2026 16:37:09 +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 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:

...
> > > > +struct adf41513_pll_settings {
> > > > +	enum adf41513_pll_mode mode;
> > > 
> > > Sounds to me like a room to improve the layout here,
> > 
> > I am targeting a 32-bit cpu, just moved in_value down:
> > would this be fine? (pahole output):
> 
> Likely.
> 
> > struct adf41513_pll_settings {
> >         enum adf41513_pll_mode     mode;                 /*     0     4 */
> 
> Wondering if this can be shorter if moved down...
> 
> >         u8                         r_counter;            /*     4     1 */
> >         u8                         ref_doubler;          /*     5     1 */
> >         u8                         ref_div2;             /*     6     1 */
> >         u8                         prescaler;            /*     7     1 */
> >         u64                        target_frequency_uhz; /*     8     8 */
> >         u64                        actual_frequency_uhz; /*    16     8 */
> >         u64                        pfd_frequency_uhz;    /*    24     8 */
> >         u32                        frac1;                /*    32     4 */
> >         u32                        frac2;                /*    36     4 */
> >         u32                        mod2;                 /*    40     4 */
> >         u16                        int_value;            /*    44     2 */
> > 
> >         /* size: 48, cachelines: 1, members: 12 */
> >         /* padding: 2 */
> >         /* last cacheline: 48 bytes */
> > };
> 
> ...at least I have had in mind that "mode" should be moved to be near
> to "int_value". But I think it will take 4 bytes still as we don't use
> short enums compile wise.
> 

As you mentioned without short-enums it does not make any difference.

> > > > +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.
I am preparing V5 to use simple_strtoull. Thanks for early review
and suggestions.

Kind regards,

Rodrigo Alencar