Hi!
Sorry for the delay. Vacation...
On 2020-07-26 14:41, Jonathan Cameron wrote:
> On Tue, 21 Jul 2020 01:16:55 +0200
> Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:
>
>> Hi Jonathan,
>>
>> Le sam. 15 févr. 2020 à 18:32, Jonathan Cameron <jic23@xxxxxxxxxx> a
>> écrit :
>>> On Mon, 10 Feb 2020 19:54:38 -0300
>>> Paul Cercueil <paul@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
>>>> ---
>>>> 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.
Right, I didn't originally add scaled writing as
1. I don't need it.
2. It's a rats nest, IIRC some drivers are picky in what they take and
you would need some kind of matrix of how to best handle the different
conversion cases. I just didn't want to go there, and this patch
feels far too simple to be adequate. But then again, maybe my memory is
poorer that I thought...
Cheers,
Peter
