linux-kernel - Re: [PATCH v1 1/9] iio: inkern: always apply scale requested by consumer

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Date:   Mon, 31 May 2021 15:39:40 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Liam Beguin <liambeguin@...il.com>, jic23@...nel.org,
        lars@...afoo.de, pmeerw@...erw.net
Cc:     linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org, robh+dt@...nel.org
Subject: Re: [PATCH v1 1/9] iio: inkern: always apply scale requested by
 consumer

Hi!

On 2021-05-30 02:59, Liam Beguin wrote:
> From: Liam Beguin <lvb@...hos.com>
> 
> When a consumer calls iio_read_channel_processed() and no scaling is
> available on the channel, it's assumed that the scale is one and the raw
> value is returned as expected.
> 
> On the other hand, if the consumer calls iio_convert_raw_to_processed()
> the scaling factor requested by the consumer is not applied.
> This for example causes the consumer to process mV when expecting uV.
> 
> Make sure to always apply the scaling factor requested by the consumer.
> 
> Signed-off-by: Liam Beguin <lvb@...hos.com>
> ---
>  drivers/iio/inkern.c | 6 +-----
>  1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/drivers/iio/inkern.c b/drivers/iio/inkern.c
> index db77a2d4a56b..4b6a8e11116a 100644
> --- a/drivers/iio/inkern.c
> +++ b/drivers/iio/inkern.c
> @@ -601,11 +601,7 @@ static int iio_convert_raw_to_processed_unlocked(struct iio_channel *chan,
>  	scale_type = iio_channel_read(chan, &scale_val, &scale_val2,
>  					IIO_CHAN_INFO_SCALE);
>  	if (scale_type < 0) {
> -		/*
> -		 * Just pass raw values as processed if no scaling is
> -		 * available.
> -		 */
> -		*processed = raw;
> +		*processed = raw * scale;

I would keep the comment. Sure, it's now completely confusing since it's from
before the function had a scale parameter. Perhaps reword it to talk about
"no channel scaling" instead of plain old "no scaling"?

Also, this looks like a bugfix, no more, no less, and should perhaps have a
fixes tag?

Cheers,
Peter

>  		return 0;
>  	}
>  
>