linux-kernel - Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light Sensor

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Date:   Mon, 6 Nov 2023 11:13:55 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Subhajit Ghosh <subhajit.ghosh@...aklogic.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Matti Vaittinen <mazziesaccount@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Paul Gazzillo <paul@...zz.com>,
        Matt Ranostay <matt@...ostay.sg>,
        Stefan Windfeldt-Prytz <stefan.windfeldt-prytz@...s.com>,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] iio: light: Add support for APDS9306 Light
 Sensor

On Tue, 31 Oct 2023 19:08:08 +1030
Subhajit Ghosh <subhajit.ghosh@...aklogic.com> wrote:

> >   
> >> +static struct iio_event_spec apds9306_event_spec_als[] = {
> >> +	{
> >> +		.type = IIO_EV_TYPE_THRESH,
> >> +		.dir = IIO_EV_DIR_RISING,
> >> +		.mask_shared_by_all = BIT(IIO_EV_INFO_VALUE),
> >> +	}, {
> >> +		.type = IIO_EV_TYPE_THRESH,
> >> +		.dir = IIO_EV_DIR_FALLING,
> >> +		.mask_shared_by_all = BIT(IIO_EV_INFO_VALUE),
> >> +	}, {
> >> +		.type = IIO_EV_TYPE_THRESH,
> >> +		.mask_shared_by_all = BIT(IIO_EV_INFO_PERIOD),
> >> +	}, {
> >> +		.type = IIO_EV_TYPE_THRESH_ADAPTIVE,
> >> +		.mask_shared_by_all = BIT(IIO_EV_INFO_VALUE) |
> >> +			BIT(IIO_EV_INFO_ENABLE),
> >> +	}, {
> >> +		.type = IIO_EV_TYPE_THRESH,
> >> +		.mask_separate = BIT(IIO_EV_INFO_ENABLE),  
> > This matches an entry above for type. Don't have separate entries.  
> >> +	},
> >> +};
> >> +
> >> +static struct iio_event_spec apds9306_event_spec_clear[] = {
> >> +	{
> >> +		.type = IIO_EV_TYPE_THRESH,
> >> +		.mask_separate = BIT(IIO_EV_INFO_ENABLE),
> >> +	},
> >> +};
> >> +
> >> +#define APDS9306_CHANNEL(_type) \
> >> +	.type = _type, \
> >> +	.info_mask_shared_by_all = BIT(IIO_CHAN_INFO_INT_TIME) | \
> >> +		BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_SAMP_FREQ), \
> >> +	.info_mask_shared_by_all_available = BIT(IIO_CHAN_INFO_INT_TIME) | \
> >> +		BIT(IIO_CHAN_INFO_SCALE) | BIT(IIO_CHAN_INFO_SAMP_FREQ), \  
> > 
> > Scale on the intensity channel is interesting...  What are the units?
> > There tend not to be any well defined units for intensity (as opposed
> > to illuminance).  There may be gain on the signal, but it won't be in untils
> > that map directly to a scale userspace should apply.  This is one of the
> > rare reasons for using the HARDWARE_GAIN element of the ABI.
> > 
> > A tricky corner however as relationship between raw value and hardwaregain
> > is not tightly defined (as it can be really weird!)  
> Hi Jonathan,
> 
> Thank you for taking time for reviewing and clearing all my tiny doubts and
> queries especially for the dt and versioning part. Much appreciated.
> 
> In the above case, should I not expose scale for the "clear" channel? Rather,
> how should I expose the "clear" channel to userspace?
What is the scale?  What units to you get after applying it?

I suspect it's not well defined.

Not sure what we've done in similar cases in the past.  Perhaps have
a look at those.  There may be precedence for still using scale.

I'm about to jump on a long haul flight (delayed - sigh) so don't have
time to look myself!

Jonathan

> 
> Regards,
> Subhajit Ghosh
> 
> >   
> >> +
> >> +static struct iio_chan_spec apds9306_channels_without_events[] = {
> >> +	{
> >> +		APDS9306_CHANNEL(IIO_LIGHT)
> >> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> >> +	}, {
> >> +		APDS9306_CHANNEL(IIO_INTENSITY)
> >> +		.channel2 = IIO_MOD_LIGHT_CLEAR,
> >> +		.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
> >> +		.modified = 1,
> >> +	},
> >> +};  
> >   
> 
>