linux-kernel - Re: [PATCH 2/2] iio: afe: rescale: Implement write

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Message-ID: <20200726134123.456bf3ad@archlinux>
Date:   Sun, 26 Jul 2020 13:41:23 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Peter Rosin <peda@...ntia.se>, od@...c.me,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] iio: afe: rescale: Implement write_raw

On Tue, 21 Jul 2020 01:16:55 +0200
Paul Cercueil <paul@...pouillou.net> wrote:

> Hi Jonathan,
> 
> Le sam. 15 févr. 2020 à 18:32, Jonathan Cameron <jic23@...nel.org> a 
> écrit :
> > On Mon, 10 Feb 2020 19:54:38 -0300
> > Paul Cercueil <paul@...pouillou.net> wrote:
> >   
> >>  Implement write_raw by converting the value if writing the scale, or
> >>  just calling the managed channel driver's write_raw otherwise.
> >> 
> >>  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> >>  ---
> >>   drivers/iio/afe/iio-rescale.c | 22 ++++++++++++++++++++++
> >>   1 file changed, 22 insertions(+)
> >> 
> >>  diff --git a/drivers/iio/afe/iio-rescale.c 
> >> b/drivers/iio/afe/iio-rescale.c
> >>  index 95802d9ee25e..a48f6af9316d 100644
> >>  --- a/drivers/iio/afe/iio-rescale.c
> >>  +++ b/drivers/iio/afe/iio-rescale.c
> >>  @@ -35,6 +35,27 @@ struct rescale {
> >>   	int *scale_data;
> >>   };
> >> 
> >>  +static int rescale_write_raw(struct iio_dev *indio_dev,
> >>  +			     struct iio_chan_spec const *chan,
> >>  +			     int val, int val2, long mask)
> >>  +{
> >>  +	struct rescale *rescale = iio_priv(indio_dev);
> >>  +	unsigned long long tmp;
> >>  +
> >>  +	switch (mask) {
> >>  +	case IIO_CHAN_INFO_SCALE:
> >>  +		tmp = val * 1000000000LL;
> >>  +		do_div(tmp, rescale->numerator);
> >>  +		tmp *= rescale->denominator;
> >>  +		do_div(tmp, 1000000000LL);
> >>  +		return iio_write_channel_attribute(rescale->source, tmp, 0,
> >>  +						   IIO_CHAN_INFO_SCALE);  
> > 
> > Why is val2 always 0?  Won't that only work if the backend device
> > has integer scales?  
> 
> Sorry, somehow I didn't see your answer.
> 
> Indeed, this will only work if the backend device has integer scales, 
> but what should I do? Just pass 'val2' instead of 0? Will the value be 
> correct if I only apply the scale ratio to 'val'?

I think you'll need to include it through the calculation. Given you
premultiply by 1000000000LL it should be easy enough to do.
Then for the final do_div you can easily work out the val2 part.

I'm not sure we currently have an inkern interface to get the type
of the channel attribute value though.  You may need to add one.

Jonathan



> 
> Cheers,
> -Paul
> 
> 
> >>  +	default:
> >>  +		return iio_write_channel_attribute(rescale->source,
> >>  +						   val, val2, mask);
> >>  +	}
> >>  +}
> >>  +
> >>   static int rescale_convert(struct rescale *rescale, int type,
> >>   			   const int val, const int val2,
> >>   			   int *val_out, int *val2_out)
> >>  @@ -110,6 +131,7 @@ static int rescale_read_avail(struct iio_dev 
> >> *indio_dev,
> >>   }
> >> 
> >>   static const struct iio_info rescale_info = {
> >>  +	.write_raw = rescale_write_raw,
> >>   	.read_raw = rescale_read_raw,
> >>   	.read_avail = rescale_read_avail,
> >>   };  
> >   
> 
>