Messages in this thread | | | Date | Mon, 13 Mar 2023 11:39:06 +0200 | From | Matti Vaittinen <> | Subject | Re: [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor |
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On 3/12/23 17:36, Jonathan Cameron wrote: > On Sun, 5 Mar 2023 14:22:51 +0200 > Matti Vaittinen <mazziesaccount@gmail.com> wrote: > >> On 3/4/23 22:17, Jonathan Cameron wrote: >>> On Thu, 2 Mar 2023 12:58:59 +0200 >>> Matti Vaittinen <mazziesaccount@gmail.com> 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?
That's what I did originally have. But then I noticed we can get slightly better accuracy than that. Hence I switched to mLux and added the scale.
> 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.
Ah. This makes sense then. Maybe it would be worth adding a warning to IIO-core if drivers set both the SCALE and PROCESSED info bits?
So, I need to select between the simplicity or better accuracy here? :/ I really hate ending up making choices like this without knowing all the real use-cases :( And it happens a lot for me. Well, I guess I'll drop the scale, use luxes and go with the PROCESSED data. My understanding is that the "thing" with the sensor is a wide-range for wavelengths, not the accuracy. So, maybe luxes are just good enough - and again, users needing something more accurate can utilize the raw intensity channels.
> > In the rare case where you do get SCALE and PROCESSED it's there to allow > for changes in the underlying signal measurement that are eaten up in the > computation needed to get to PROCESSED - that is they have no visible > affect (beyond range changes etc).
Oh, Ok. So there is a valid case for setting both SCALE and PROCESSED. Then we can't add teh warning I assume :(
Yours, -- Matti
-- Matti Vaittinen Linux kernel developer at ROHM Semiconductors Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
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