linux-kernel - Re: [PATCH v7 1/5] iio: core: Add IIO_VAL

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Message-ID: <9fd7f08f-51cc-4155-a5e2-c6ba2f1c4897@baylibre.com>
Date: Tue, 26 Aug 2025 12:00:05 -0500
From: David Lechner <dlechner@...libre.com>
To: Ben Collins <bcollins@...nel.org>, Jonathan Cameron <jic23@...nel.org>,
 Nuno Sá <nuno.sa@...log.com>,
 Andy Shevchenko <andy@...nel.org>,
 Antoniu Miclaus <antoniu.miclaus@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>
Cc: linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/5] iio: core: Add IIO_VAL_EMPTY type

On 8/25/25 7:10 PM, Ben Collins wrote:
> In certain situations it may be necessary to return nothing when reading
> an attribute.
> 
> For example, when a driver has a filter_type of "none" it should not
> print any information for frequency or available frequencies.
> 
> Signed-off-by: Ben Collins <bcollins@...nel.org>
> ---
>  drivers/iio/industrialio-core.c | 1 +
>  include/linux/iio/types.h       | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 159d6c5ca3cec3f5c37ee9b85ef1681cca36f5c7..e4ff5b940223ab58bf61b394cc9357cd3674cfda 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -702,6 +702,7 @@ static ssize_t __iio_format_value(char *buf, size_t offset, unsigned int type,
>  	case IIO_VAL_INT_64:
>  		tmp2 = (s64)((((u64)vals[1]) << 32) | (u32)vals[0]);
>  		return sysfs_emit_at(buf, offset, "%lld", tmp2);
> +	case IIO_VAL_EMPTY:
>  	default:
>  		return 0;
>  	}
> diff --git a/include/linux/iio/types.h b/include/linux/iio/types.h
> index ad2761efcc8315e1f9907d2a7159447fb463333e..261745c2d94e582bcca1a2abb297436e8314c930 100644
> --- a/include/linux/iio/types.h
> +++ b/include/linux/iio/types.h
> @@ -32,6 +32,7 @@ enum iio_event_info {
>  #define IIO_VAL_FRACTIONAL 10
>  #define IIO_VAL_FRACTIONAL_LOG2 11
>  #define IIO_VAL_CHAR 12
> +#define IIO_VAL_EMPTY 13
>  
>  enum iio_available_type {
>  	IIO_AVAIL_LIST,
> 

This is an interesting idea, but I think it would be a lot of work
to teach existing userspace tools to handle this new possibility.

On top of that, I'm not quite convinced it is necessary. If a numeric
value is undefined, then there is already a well known expression for
that: "nan". Or in the case of this series, the 3dB point when the
filter is disable could also be considered "inf". Using these would have
a better chance of working with existing userspace tools since things
like `scanf()` can already handle these.