linux-kernel - Re: [PATCH] iio: light: Add support for Capella CM3323 color/light sensor

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Message-ID: <CAEnQRZDtkQiqxLQZ6f4SJW29sDtMvgFe55ecTFMKfi6O7rcNdg@mail.gmail.com>
Date:	Mon, 2 Mar 2015 11:57:02 +0200
From:	Daniel Baluta <daniel.baluta@...el.com>
To:	Daniel Baluta <daniel.baluta@...el.com>
Cc:	Jonathan Cameron <jic23@...nel.org>,
	Kevin Tsai <ktsai@...ellamicro.com>,
	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: light: Add support for Capella CM3323 color/light sensor

On Sun, Jan 25, 2015 at 12:50 PM, Daniel Baluta <daniel.baluta@...el.com> wrote:
> On Sun, Jan 25, 2015 at 12:27 PM, Jonathan Cameron <jic23@...nel.org> wrote:
>> On 22/01/15 10:10, Daniel Baluta wrote:
>>> Minimal implementation providing raw light intensity and illuminance
>>> readings. For illuminance user can compute lux values using raw readings
>>> and scale.
>>>
>>> This driver also supports CM3323E sensor chip.
>>>
>>> Cc: Kevin Tsai <ktsai@...ellamicro.com>
>>> Signed-off-by: Daniel Baluta <daniel.baluta@...el.com>
>>
>> Hi Daniel,
>>
>> My only real question on this one is whether using the 'green' channel
>> and pretending it is a measure of illuminance is a good idea or whether
>> we are better leaving that decision to userspace...
>>
>> I'm guessing the reason it is green rather than clear is that
>> the clear is letting infrared through and we don't have an additional
>> infrared sensor available to allow that component to be removed?
>
> Hi Jonathan,
>
> <snip>
>>> +#define CM3323_COLOR_CHANNEL(_color, _addr) {\
>>> +     .type = IIO_INTENSITY, \
>>> +     .modified = 1, \
>>> +     .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
>>> +     .info_mask_shared_by_all = BIT(IIO_CHAN_INFO_INT_TIME), \
>>> +     .channel2 = IIO_MOD_LIGHT_##_color, \
>>> +     .address = _addr, \
>>> +}
>>> +
>>> +/*
>>> + * CM3323's GREEN channel is used for reading illuminance
>> That's impressively random and unlikely to be anywhere near correct
>> pretty much all the time!
>>
>> I'd personally prefer just not providing an illuminance channel
>> and leaving it up to userspace to make the decision on whether the
>> green channel is good enough...
>
> Datasheet says that the GREEN channel should be used
> for getting illuminance readings. I'm not sure if this is
> totally random.
>
> I understand your worries, perhaps Kevin could 'enlighten' us here.
>
> I would  prefer to have the illuminance channel exported from
> IIO because there are already userspace applications/frameworks
>  written and tested for ALS that use IIO illuminance channel.
> We want to use this driver without modifying user space.
>
> Of course, one option for the moment would be to only export
> the INTENSITY channels as per your recommendation and
> to decide later what to do for the LIGHT channel.

Hi Kevin,

Could you tell us how reliable is using the GREEN channel for getting
illuminance readings?

If no objection, I will resend this driver exposing only INTENSITY channels
for the moment.

thanks,
Daniel.
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