On Tue, 14 Mar 2023 11:39:22 +0200
Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> On 3/12/23 17:36, Jonathan Cameron wrote:
> > On Sun, 5 Mar 2023 14:22:51 +0200
> > Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> >
> >> On 3/4/23 22:17, Jonathan Cameron wrote:
> >>> On Thu, 2 Mar 2023 12:58:59 +0200
> >>> Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
>
> //snip
>
> >>>
> >>>> +static const struct iio_chan_spec bu27034_channels[] = {
> >>>> + {
> >>>> + .type = IIO_LIGHT,
> >>>> + .info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED) |
> >>>> + BIT(IIO_CHAN_INFO_SCALE),
> >>>
> >>> What is this scale for?
> >>
> >> The scale is to inform users that we return data using milli lux.
> >>
> >>> Given the channel is computed from various different inputs, is there a
> >>> clear definition of how it is scaled? What does a write to it mean?
> >>
> >> Nothing. writing anything else but milli lux scale fails with -EINVAL.
> >>
> >> I guess I am doing something in an unusual way here :) Do you have a
> >> suggestion for me?
> >
> > Return data in lux? Or return it as INFO_RAW - thus making it clear
> > that the reading is not in expected units and a conversion must be
> > applied by userspace. SCALE is not applied to PROCESSED by userspace.
> >
>
> I just noticed a thing. I used the iio_generic_buffer to test the
> changes - and it got the channel values scaled to luxes even for the
> PROCESSED channel. So, it seems to me the iio_generic_buffer does apply
> the scale for PROCESSED channels too. I think that is slightly
> misleading. Oh, and this is not intended to be a complaint - just a
> report that there might be some room for an improvement :)
Ah. Looks like the code doesn't have any check on whether the sysfs
read is _raw or _processed which is kind of understandable.
This may be the first case where those have both applied on a channel
that is available via buffered route.
Given processed channels are rarely IIO_VAL_INT which is kind of necessary
to poke it in the buffered route, that may well be true.
Jonathan
>
> Yours,
> -- Matti
>
