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

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Message-ID: <307f93f9-2a41-4704-ac4f-8d1e427e5060@tweaklogic.com>
Date:   Mon, 6 Nov 2023 22:34:40 +1030
From:   Subhajit Ghosh <subhajit.ghosh@...aklogic.com>
To:     Jonathan Cameron <jic23@...nel.org>
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 6/11/23 21:43, Jonathan Cameron wrote:
> 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?
The scale is in Lux. The output after applying is Lux.
> 
> 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.
Sure, I'll look it up.
> 
> I'm about to jump on a long haul flight (delayed - sigh) so don't have
> time to look myself!
> 
No worries. I will update notes and application in next version.
Have a good trip to where ever you are going. Are you coming to Australia
by any chance?
Thanks for the reply.

Regards,
Subhajit Ghosh