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

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Message-Id: <7CJSDQ.D8SUUUMJPNE02@crapouillou.net>
Date:   Tue, 21 Jul 2020 01:16:55 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Jonathan Cameron <jic23@...nel.org>
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

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'?

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,
>>   };
>