linux-kernel - Re: [PATCH 2/4] iio: add processed write API

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Message-ID: <decdb75c-b61e-4e0f-bddd-cfc8986f3b6f@baylibre.com>
Date: Tue, 16 Sep 2025 14:23:04 -0500
From: David Lechner <dlechner@...libre.com>
To: Romain Gantois <romain.gantois@...tlin.com>,
 Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Jonathan Cameron <jic23@...nel.org>,
 Nuno Sá <nuno.sa@...log.com>,
 Andy Shevchenko <andy@...nel.org>
Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
 linux-iio@...r.kernel.org
Subject: Re: [PATCH 2/4] iio: add processed write API

On 9/16/25 5:24 AM, Romain Gantois wrote:
> Add a function to allow IIO consumers to write a processed value to a
> channel.
> 
> Signed-off-by: Romain Gantois <romain.gantois@...tlin.com>
> ---
>  drivers/iio/inkern.c         | 99 ++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iio/consumer.h | 17 ++++++++
>  2 files changed, 116 insertions(+)
> 
> diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> index c174ebb7d5e6d183674b7ffb15c4ce0f65fa3aed..6486fdb7c66a4c84312541f0f42cc24469972a9c 100644
> --- a/drivers/iio/inkern.c
> +++ b/drivers/iio/inkern.c
> @@ -598,6 +598,85 @@ int iio_read_channel_average_raw(struct iio_channel *chan, int *val)
>  }
>  EXPORT_SYMBOL_GPL(iio_read_channel_average_raw);
>  
> +static int iio_convert_processed_to_raw_unlocked(struct iio_channel *chan,
> +						 int processed, int *raw,
> +						 unsigned int scale)
> +{
> +	int scale_type, scale_val, scale_val2;
> +	int offset_type, offset_val, offset_val2;
> +	s64 tmp_num, tmp_den;
> +
> +	scale_type = iio_channel_read(chan, &scale_val, &scale_val2,
> +				      IIO_CHAN_INFO_SCALE);
> +	if (scale_type >= 0) {
> +		switch (scale_type) {
> +		case IIO_VAL_INT:
> +			tmp_num = processed;
> +			tmp_den = scale_val;
> +			break;
> +		case IIO_VAL_INT_PLUS_MICRO:
> +			tmp_num = (s64)processed * 1000000LL;
> +
> +			if (scale_val2 < 0) {
> +				tmp_den = (s64)scale_val * 1000000LL - (s64)scale_val2;
> +				tmp_den *= -1;
> +			} else {
> +				tmp_den = (s64)scale_val * 1000000LL + (s64)scale_val2;
> +			}
> +
> +			break;
> +		case IIO_VAL_INT_PLUS_NANO:
> +			tmp_num = (s64)processed * 1000000000LL;
> +
> +			if (scale_val2 < 0) {
> +				tmp_den = (s64)scale_val * 1000000000LL - (s64)scale_val2;
> +				tmp_den *= -1;
> +			} else {
> +				tmp_den = (s64)scale_val * 1000000000LL + (s64)scale_val2;
> +			}
> +
> +			break;
> +		case IIO_VAL_FRACTIONAL:
> +			tmp_num = (s64)processed * (s64)scale_val2;
> +			tmp_den = scale_val;
> +			break;
> +		case IIO_VAL_FRACTIONAL_LOG2:
> +			tmp_num = (s64)processed << scale_val2;
> +			tmp_den = scale_val;
> +			break;
> +		default:
> +			return -EINVAL;
> +		}
> +
> +		tmp_den *= scale;
> +
> +		*raw = div64_s64(tmp_num, tmp_den);
> +	}

It can be quite tricky to get all of these combinations right. I would
prefer if added some unit tests like we did in [1].

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/jic23/iio.git/commit/?h=testing&id=c732e60ee10ed0611a59513cbf9c8d35fbe7cf65

> +
> +	offset_type = iio_channel_read(chan, &offset_val, &offset_val2,
> +				       IIO_CHAN_INFO_OFFSET);
> +	if (offset_type >= 0) {
> +		switch (offset_type) {
> +		case IIO_VAL_INT:
> +		case IIO_VAL_INT_PLUS_MICRO:
> +		case IIO_VAL_INT_PLUS_NANO:
> +			break;
> +		case IIO_VAL_FRACTIONAL:
> +			offset_val /= offset_val2;
> +			break;
> +		case IIO_VAL_FRACTIONAL_LOG2:
> +			offset_val >>= offset_val2;
> +			break;
> +		default:
> +			return -EINVAL;
> +		}
> +
> +		*raw -= offset_val;
> +	}
> +
> +	return 0;
> +}