Re: [PATCH v16 08/14] iio: core: add decimal value formatting into 64-bit value

["Nuno Sá" <noname.nuno@gmail.com>]

On Thu, 2026-06-04 at 10:59 +0100, Rodrigo Alencar via B4 Relay wrote:
> From: Rodrigo Alencar <rodrigo.alencar@analog.com>
> 
> Create new format types for iio values (IIO_VAL_DECIMAL64_*), which
> defines the representation of fixed decimal point values into a single
> 64-bit number. This new format increases the range of represented values,
> allowing for integer parts greater than 2^32, as bits are not "wasted"
> in the fractional part, which can be seen in IIO_VAL_INT_PLUS_MICRO and
> IIO_VAL_INT_PLUS_NANO. Helpers are created to compose and decompose 64-bit
> decimals into integer values used in IIO formatting interfaces, which
> creates consistency and avoid error-prone manual assignments when using
> wordpart macros. When doing the parsing, kstrtodec64() is used with the
> scale defined by the specific decimal format type.
> 
> Signed-off-by: Rodrigo Alencar <rodrigo.alencar@analog.com>
> ---

Reviewed-by: Nuno Sá <nuno.sa@analog.com>

>  drivers/iio/industrialio-core.c | 49 ++++++++++++++++++++++++++++++++---------
>  include/linux/iio/types.h       | 20 +++++++++++++++++
>  2 files changed, 59 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index ffe0dc49c4b9..93c2540d4cd2 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -19,6 +19,7 @@
>  #include <linux/idr.h>
>  #include <linux/kdev_t.h>
>  #include <linux/kernel.h>
> +#include <linux/math64.h>
>  #include <linux/module.h>
>  #include <linux/mutex.h>
>  #include <linux/poll.h>
> @@ -26,7 +27,6 @@
>  #include <linux/sched.h>
>  #include <linux/slab.h>
>  #include <linux/wait.h>
> -#include <linux/wordpart.h>
>  
>  #include <linux/iio/buffer.h>
>  #include <linux/iio/buffer_impl.h>
> @@ -656,6 +656,7 @@ static ssize_t __iio_format_value(char *buf, size_t offset,
> unsigned int type,
>  				  int size, const int *vals)
>  {
>  	int tmp0, tmp1;
> +	int l = 0;
>  	s64 tmp2;
>  	bool scale_db = false;
>  
> @@ -699,7 +700,6 @@ static ssize_t __iio_format_value(char *buf, size_t offset,
> unsigned int type,
>  	case IIO_VAL_INT_MULTIPLE:
>  	{
>  		int i;
> -		int l = 0;
>  
>  		for (i = 0; i < size; ++i)
>  			l += sysfs_emit_at(buf, offset + l, "%d ", vals[i]);
> @@ -708,8 +708,25 @@ static ssize_t __iio_format_value(char *buf, size_t offset,
> unsigned int type,
>  	case IIO_VAL_CHAR:
>  		return sysfs_emit_at(buf, offset, "%c", (char)vals[0]);
>  	case IIO_VAL_INT_64:
> -		tmp2 = (s64)((((u64)vals[1]) << 32) | (u32)vals[0]);
> -		return sysfs_emit_at(buf, offset, "%lld", tmp2);
> +		return sysfs_emit_at(buf, offset, "%lld",
> +				     iio_val_s64_compose(vals[0], vals[1]));
> +	case IIO_VAL_DECIMAL64_MILLI:
> +	case IIO_VAL_DECIMAL64_MICRO:
> +	case IIO_VAL_DECIMAL64_NANO:
> +	case IIO_VAL_DECIMAL64_PICO:
> +	{
> +		int scale = type - IIO_VAL_DECIMAL64_BASE;
> +		s64 frac;
> +
> +		tmp2 = div64_s64_rem(iio_val_s64_compose(vals[0], vals[1]),
> +				     int_pow(10, scale), &frac);
> +		if (tmp2 == 0 && frac < 0)
> +			l += sysfs_emit_at(buf, offset, "-");
> +
> +		l += sysfs_emit_at(buf, offset + l, "%lld.%0*lld", tmp2, scale,
> +				   abs(frac));
> +		return l;
> +	}
>  	default:
>  		return 0;
>  	}
> @@ -979,6 +996,7 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
>  	struct iio_dev_attr *this_attr = to_iio_dev_attr(attr);
>  	int ret, fract_mult = 100000;
> +	int type, dec_scale = 0;
>  	int integer, fract = 0;
>  	long long integer64;
>  	bool is_char = false;
> @@ -989,9 +1007,11 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  	if (!indio_dev->info->write_raw)
>  		return -EINVAL;
>  
> -	if (indio_dev->info->write_raw_get_fmt)
> -		switch (indio_dev->info->write_raw_get_fmt(indio_dev,
> -			this_attr->c, this_attr->address)) {
> +	if (indio_dev->info->write_raw_get_fmt) {
> +		type = indio_dev->info->write_raw_get_fmt(indio_dev,
> +							  this_attr->c,
> +							  this_attr->address);
> +		switch (type) {
>  		case IIO_VAL_INT:
>  			fract_mult = 0;
>  			break;
> @@ -1007,12 +1027,19 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  		case IIO_VAL_CHAR:
>  			is_char = true;
>  			break;
> +		case IIO_VAL_DECIMAL64_MILLI:
> +		case IIO_VAL_DECIMAL64_MICRO:
> +		case IIO_VAL_DECIMAL64_NANO:
> +		case IIO_VAL_DECIMAL64_PICO:
> +			dec_scale = type - IIO_VAL_DECIMAL64_BASE;
> +			fallthrough;
>  		case IIO_VAL_INT_64:
>  			is_64bit = true;
>  			break;
>  		default:
>  			return -EINVAL;
>  		}
> +	}
>  
>  	if (is_char) {
>  		char ch;
> @@ -1021,12 +1048,14 @@ static ssize_t iio_write_channel_info(struct device *dev,
>  			return -EINVAL;
>  		integer = ch;
>  	} else if (is_64bit) {
> -		ret = kstrtoll(buf, 0, &integer64);
> +		if (dec_scale)
> +			ret = kstrtodec64(buf, dec_scale, &integer64);
> +		else
> +			ret = kstrtoll(buf, 0, &integer64);
>  		if (ret)
>  			return ret;
>  
> -		fract = upper_32_bits(integer64);
> -		integer = lower_32_bits(integer64);
> +		iio_val_s64_decompose(integer64, &integer, &fract);
>  	} else {
>  		ret = __iio_str_to_fixpoint(buf, fract_mult, &integer, &fract,
>  					    scale_db);
> diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
> index 4e3099defc1d..924ac9dc6893 100644
> --- a/include/linux/iio/types.h
> +++ b/include/linux/iio/types.h
> @@ -7,6 +7,9 @@
>  #ifndef _IIO_TYPES_H_
>  #define _IIO_TYPES_H_
>  
> +#include <linux/types.h>
> +#include <linux/wordpart.h>
> +
>  #include <uapi/linux/iio/types.h>
>  
>  enum iio_event_info {
> @@ -34,6 +37,23 @@ enum iio_event_info {
>  #define IIO_VAL_FRACTIONAL_LOG2 11
>  #define IIO_VAL_CHAR 12
>  
> +#define IIO_VAL_DECIMAL64_BASE		32
> +#define IIO_VAL_DECIMAL64_MILLI		(IIO_VAL_DECIMAL64_BASE + 3)
> +#define IIO_VAL_DECIMAL64_MICRO		(IIO_VAL_DECIMAL64_BASE + 6)
> +#define IIO_VAL_DECIMAL64_NANO		(IIO_VAL_DECIMAL64_BASE + 9)
> +#define IIO_VAL_DECIMAL64_PICO		(IIO_VAL_DECIMAL64_BASE + 12)
> +
> +static inline s64 iio_val_s64_compose(s32 val0, s32 val1)
> +{
> +	return (s64)(((u64)val1 << 32) | (u32)val0);
> +}
> +
> +static inline void iio_val_s64_decompose(s64 dec64, s32 *val0, s32 *val1)
> +{
> +	*val0 = lower_32_bits(dec64);
> +	*val1 = upper_32_bits(dec64);
> +}
> +
>  enum iio_available_type {
>  	IIO_AVAIL_LIST,
>  	IIO_AVAIL_RANGE,