Re: [PATCH v2 2/5] iio: add processed write API

[David Lechner <dlechner@baylibre.com>]

On 9/25/25 7:37 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@bootlin.com>
> ---
>  drivers/iio/inkern.c         | 120 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iio/consumer.h |  36 +++++++++++++
>  2 files changed, 156 insertions(+)
> 
> diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> index 2a1ecef2b82007f5ee8e8d0f8b35846bc4d2f94a..a6ec724b7c1fb197e6261c1162f8315deda20fd7 100644
> --- a/drivers/iio/inkern.c
> +++ b/drivers/iio/inkern.c
> @@ -631,6 +631,57 @@ int iio_multiply_value(int *result, s64 multiplier,
>  }
>  EXPORT_SYMBOL_GPL(iio_multiply_value);
>  
> +int iio_divide_by_value(int *result, s64 numerator,
> +			unsigned int type, int val, int val2)
> +{
> +	s64 tmp_num, tmp_den;
> +
> +	switch (type) {
> +	case IIO_VAL_INT:
> +		tmp_num = numerator;
> +		tmp_den = val;
> +		break;
> +	case IIO_VAL_INT_PLUS_MICRO:
> +	case IIO_VAL_INT_PLUS_NANO:
> +		switch (type) {
> +		case IIO_VAL_INT_PLUS_MICRO:
> +			tmp_num = MICRO;
> +			tmp_den = MICRO;
> +			break;
> +
> +		case IIO_VAL_INT_PLUS_NANO:
> +			tmp_num = NANO;
> +			tmp_den = NANO;
> +			break;
> +		}
> +
> +		tmp_num *= (s64)numerator;
> +		tmp_den = (s64)abs(val) * tmp_den + (s64)abs(val2);
> +
> +		if (val < 0 || val2 < 0)
> +			tmp_num *= -1;
> +
> +		break;
> +	case IIO_VAL_FRACTIONAL:
> +		tmp_num = (s64)numerator * (s64)val2;
> +		tmp_den = val;
> +		break;
> +	case IIO_VAL_FRACTIONAL_LOG2:
> +		tmp_num = (s64)numerator << val2;
> +		tmp_den = val;
> +		break;
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	if (!tmp_den)
> +		return -ERANGE;
> +
> +	*result = div64_s64(tmp_num, tmp_den);
> +
> +	return IIO_VAL_INT;
> +}
> +
>  static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan,
>  						 int raw, int *processed,
>  						 unsigned int scale)
> @@ -699,6 +750,53 @@ int iio_convert_raw_to_processed(struct iio_channel *chan, int raw,
>  }
>  EXPORT_SYMBOL_GPL(iio_convert_raw_to_processed);
>  
> +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;
> +	int ret;
> +
> +	scale_type = iio_channel_read(chan, &scale_val, &scale_val2,
> +				      IIO_CHAN_INFO_SCALE);
> +	if (scale_type >= 0) {
> +		ret = iio_divide_by_value(raw, processed, scale_type, scale_val, scale_val2);
> +		if (ret < 0)
> +			return ret;
> +	} else {
> +		*raw = processed;
> +	}
> +
> +	if (!scale)
> +		return -ERANGE;
> +
> +	*raw = div_s64(*raw, scale);
> +
> +	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;
> +	}

There are some rounding biases in this function, but I'm not sure if
it is worth trying to make a perfectly fair function.

> +
> +	return 0;
> +}
> +
>  int iio_read_channel_attribute(struct iio_channel *chan, int *val, int *val2,
>  			       enum iio_chan_info_enum attribute)
>  {
> @@ -1035,3 +1133,25 @@ ssize_t iio_read_channel_label(struct iio_channel *chan, char *buf)
>  	return do_iio_read_channel_label(chan->indio_dev, chan->channel, buf);
>  }
>  EXPORT_SYMBOL_GPL(iio_read_channel_label);
> +
> +int iio_write_channel_processed_scale(struct iio_channel *chan, int val,
> +				      unsigned int scale)
> +{
> +	struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(chan->indio_dev);
> +	int ret, processed;
> +
> +	scoped_guard(mutex, &iio_dev_opaque->info_exist_lock) {

Can just use regular guard(mutex)() here and save some indent.

> +		if (!chan->indio_dev->info)
> +			return -ENODEV;
> +
> +		ret = iio_convert_processed_to_raw_unlocked(chan, val, &processed, scale);
> +		if (ret)
> +			return ret;
> +
> +		ret = iio_channel_write(chan, processed, 0, IIO_CHAN_INFO_RAW);

And this can return directly.

> +	}
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(iio_write_channel_processed_scale);
> +
> diff --git a/include/linux/iio/consumer.h b/include/linux/iio/consumer.h
> index c8c6261c81f934480e16854412e269207be60adc..dc84b8b4c61911d1a58427f1a9c798cae3954ac1 100644
> --- a/include/linux/iio/consumer.h
> +++ b/include/linux/iio/consumer.h
> @@ -399,6 +399,24 @@ int iio_read_channel_scale(struct iio_channel *chan, int *val,
>  int iio_multiply_value(int *result, s64 multiplier,
>  		       unsigned int type, int val, int val2);
>  
> +/**
> + * iio_divide_by_value() - Divide by an IIO value
> + * @result:	Destination pointer for the division result
> + * @numerator:	Numerator.
> + * @type:	One of the IIO_VAL_* constants. This decides how the @val
> + *		and @val2 parameters are interpreted.
> + * @val:	Denominator.
> + * @val2:	Denominator. @val2 use depends on type.
> + *
> + * Divide an s64 number by an IIO value, storing the result as
> + * IIO_VAL_INT. This is typically used for scaling.
> + *
> + * Returns:
> + * IIO_VAL_INT on success or a negative error-number on failure.
> + */
> +int iio_divide_by_value(int *result, s64 numerator,
> +			unsigned int type, int val, int val2);
> +
>  /**
>   * iio_convert_raw_to_processed() - Converts a raw value to a processed value
>   * @chan:		The channel being queried
> @@ -469,4 +487,22 @@ ssize_t iio_write_channel_ext_info(struct iio_channel *chan, const char *attr,
>   */
>  ssize_t iio_read_channel_label(struct iio_channel *chan, char *buf);
>  
> +/**
> + * iio_write_channel_processed_scale() - scale and write processed value to a given channel
> + * @chan:		The channel being queried.
> + * @val:		Value to write.
> + * @scale:		Scale factor to apply during the conversion

This could be more explicit about what sort of scaling this is.
The function divides by this factor rather than multiplies by it.

> + *
> + * This function writes a processed value to a channel. A processed value means
> + * that this value will have the correct unit and not some device internal
> + * representation. If the device does not support writing a processed value, the
> + * function will query the channel's scale and offset and write an appropriately
> + * transformed raw value.
> + *

Could be helpful even if obvious to most people...

	Context: May sleep.

> + * Return: an error code or 0.
> + *
> + */
> +int iio_write_channel_processed_scale(struct iio_channel *chan, int val,
> +				      unsigned int scale);
> +
>  #endif
>