linux-kernel - Re: [RFC] v4l2 support for thermopile devices

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Date:   Fri, 28 Oct 2016 19:59:15 -0700
From:   Matt Ranostay <matt@...ostay.consulting>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Attila Kinali <attila@...ali.ch>, Marek Vasut <marex@...x.de>
Subject: Re: [RFC] v4l2 support for thermopile devices

On Fri, Oct 28, 2016 at 2:53 PM, Hans Verkuil <hverkuil@...all.nl> wrote:
> Hi Matt,
>
> On 28/10/16 22:14, Matt Ranostay wrote:
>>
>> So want to toss a few thoughts on adding support for thermopile
>> devices (could be used for FLIR Lepton as well) that output pixel
>> data.
>> These typically aren't DMA'able devices since they are low speed
>> (partly to limiting the functionality to be in compliance with ITAR)
>> and data is piped over i2c/spi.
>>
>> My question is that there doesn't seem to be an other driver that
>> polls frames off of a device and pushes it to the video buffer, and
>> wanted to be sure that this doesn't currently exist somewhere.
>
>
> Not anymore, but if you go back to kernel 3.6 then you'll find this driver:
>
> drivers/media/video/bw-qcam.c
>
> It was for a grayscale parallel port webcam (which explains why it was
> removed in 3.7 :-) ), and it used polling to get the pixels.

Yikes parallel port, but I'll take a look at that for some reference :)

>
>> Also more importantly does the mailing list thinks it belongs in v4l2?
>
>
> I think it fits. It's a sensor, just with a very small resolution and
> infrared
> instead of visible light.
>
>> We already came up the opinion on the IIO list that it doesn't belong
>> in that subsystem since pushing raw pixel data to a buffer is a bit
>> hacky. Also could be generically written with regmap so other devices
>> (namely FLIR Lepton) could be easily supported.
>>
>> Need some input for the video pixel data types, which the device we
>> are using (see datasheet links below) is outputting pixel data in
>> little endian 16-bit of which a 12-bits signed value is used.  Does it
>> make sense to do some basic processing on the data since greyscale is
>> going to look weird with temperatures under 0C degrees? Namely a cold
>> object is going to be brighter than the hottest object it could read.
>
>
>> Or should a new V4L2_PIX_FMT_* be defined and processing done in
>> software?
>
>
> I would recommend that. It's no big deal, as long as the new format is
> documented.
>
>> Another issue is how to report the scaling value of 0.25 C
>> for each LSB of the pixels to the respecting recording application.
>
>
> Probably through a read-only control, but I'm not sure.
>
> Regards,
>
>         Hans
>
>>
>> Datasheet:
>> http://media.digikey.com/pdf/Data%20Sheets/Panasonic%20Sensors%20PDFs/Grid-EYE_AMG88.pdf
>> Datasheet:
>> https://eewiki.net/download/attachments/13599167/Grid-EYE%20SPECIFICATIONS%28Reference%29.pdf?version=1&modificationDate=1380660426690&api=v2
>>
>> Thanks,
>>
>> Matt
>> --
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>>
>