Re: [PATCH RFC v2 3/4] iio: core: use kstrtodec64() to parse fixed-point values

[Andy Shevchenko]

On Tue, Oct 13, 2026 at 10:36:46AM -0300, Rodrigo Alencar via B4 Relay wrote:

> Replace the open-coded __iio_str_to_fixpoint() parser with kstrtodec64(),
> so sysfs writes of fixed-point values also accept E notation.
> 
> The fractional part only keeps the sign when the integer part is zero,
> as before. The dB suffix for scale attributes is now handled by a separate
> iio_str_to_fixpoint_units() helper. It strips an optional trailing newline
> and the "dB" or " dB" suffix before parsing.
> 
> When there is no fractional part (fract_mult == 0, or dec_scale == 0 for
> 64-bit values), try base-autodetecting kstrtoll() first so hexadecimal
> and octal input keeps its meaning ("010" is still 8). Fall back to
> kstrtodec64() on -EINVAL to accept E notation.
> 
> As a side effect, inputs that used to be rejected for integer-only
> attributes are now accepted. An invalid octal number such as "08" is
> parsed as decimal 8, and a fractional value such as "1.5" is truncated
> to 1, matching how kstrtodec64() drops digits beyond the requested
> scale.

...

> -int iio_str_to_fixpoint(const char *str, int fract_mult,
> -			int *integer, int *fract)
> +int iio_str_to_fixpoint(const char *str, int fract_mult, int *integer,
> +			int *fract)

Keep the logical split, id est don't touch these lines, there are no changes.

...

> +static int iio_str_to_fixpoint_units(const char *str, const char *units,
> +				     int fract_mult, int *integer, int *fract)
> +{
> +	size_t units_len = strlen(units);
> +	size_t num_len = strlen(str);
> +	const char *dec_str = str;
> +	char buf[64];

> +	if (num_len && str[num_len - 1] == '\n')
> +		num_len--;
> +	if (num_len > units_len &&
> +	    !strncmp(str + num_len - units_len, units, units_len)) {

Hmm... We have strends()... Do you expect string to have garbage at the end?
In such a case dB and dBm won't be distinguishable.

> +		num_len -= units_len;
> +		if (str[num_len - 1] == ' ')
> +			num_len--;
> +		if (num_len >= sizeof(buf))
> +			return -EINVAL;
> +		memcpy(buf, str, num_len);
> +		buf[num_len] = '\0';
> +		dec_str = buf;
> +	}
> +
> +	return iio_str_to_fixpoint(dec_str, fract_mult, integer, fract);
> +}

-- 
With Best Regards,
Andy Shevchenko