Re: [PATCH v15 06/12] iio: core: add decimal value formatting into 64-bit value

["Nuno Sá" <noname.nuno@gmail.com>]

On Sun, May 31, 2026 at 09:30:49AM +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>
> ---
>  drivers/iio/industrialio-core.c | 47 +++++++++++++++++++++++++++++++++--------
>  include/linux/iio/types.h       | 30 ++++++++++++++++++++++++++
>  2 files changed, 68 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index bd6f4f9f4533..a88088cac641 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>
> @@ -655,6 +655,7 @@ 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;
>  
> @@ -698,7 +699,6 @@ 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]);
> @@ -707,8 +707,25 @@ 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]);
> +		tmp2 = iio_val_s64_from_s32s(vals);

I might be missing something but can't we just call
iio_val_s64_compose()? Likely even inline in sysfs_emit_at()?

It would match your call to iio_val_s64_decompose() below.

And the above makes me wonder if the compose()/decompose() are not the
only helpers we need? At least in terms of parameters? I mean, just
assuming we only have two integers instead of allowing s32* and opening
the door for misbehave :)?

Don't feel too strong about the above anyways!

- Nuno Sá