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

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Message-ID: <2025082614-passionate-panther-8016ba@boujee-and-buff>
Date: Tue, 26 Aug 2025 14:52:27 -0400
From: Ben Collins <bcollins@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: 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>, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 1/5] iio: core: Add IIO_VAL_EMPTY type

On Tue, Aug 26, 2025 at 12:00:05PM -0500, David Lechner wrote:
> 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.

I'm ok with "inf", but then would there also be an "inf" in available
frequencies?

This would take us all the way back to where I could just not even need
a filter_type==none and make the 3db available values:

{ inf, 0.5xxx, ... }

And inf would just be the filter is disabled.

-- 
 Ben Collins
 https://libjwt.io
 https://github.com/benmcollins
 --
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