Re: [PATCH v2 5/6] iio: light: ROHM BU27034 Ambient Light Sensor

[Matti Vaittinen]

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 :)

Yours,
	-- Matti

--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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