linux-kernel - Re: [PATCH 0/8] Input: atmel_mxt_ts - output raw touch diagnostic data via V4L

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Date:	Fri, 22 Apr 2016 16:07:42 +0100
From:	Nick Dyer <nick.dyer@...ev.co.uk>
To:	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Hans Verkuil <hverkuil@...all.nl>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-media@...r.kernel.org,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Benson Leung <bleung@...omium.org>,
	Alan Bowens <Alan.Bowens@...el.com>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Chris Healy <cphealy@...il.com>,
	Henrik Rydberg <rydberg@...math.org>,
	Andrew Duggan <aduggan@...aptics.com>,
	James Chen <james.chen@....com.tw>,
	Dudley Du <dudl@...ress.com>,
	Andrew de los Reyes <adlr@...omium.org>,
	sheckylin@...omium.org, Peter Hutterer <peter.hutterer@...-t.net>,
	Florian Echtler <floe@...terbrot.org>
Subject: Re: [PATCH 0/8] Input: atmel_mxt_ts - output raw touch diagnostic
 data via V4L

On 22/04/2016 15:45, Mauro Carvalho Chehab wrote:
> Em Fri, 22 Apr 2016 10:26:37 +0200
> Hans Verkuil <hverkuil@...all.nl> escreveu:
>> On 04/21/2016 11:31 AM, Nick Dyer wrote:
>>> This is a series of patches to add diagnostic data support to the Atmel
>>> maXTouch driver. It's a rewrite of the previous implementation which output via
>>> debugfs: it now uses a V4L2 device in a similar way to the sur40 driver.
>>>
>>> There are significant performance advantages to putting this code into the
>>> driver. The algorithm for retrieving the data has been fairly consistent across
>>> a range of chips, with the exception of the mXT1386 series (see patch).
>>>
>>> We have a utility which can read the data and display it in a useful format:
>>> 	https://github.com/ndyer/heatmap/commits/heatmap-v4l
>>>
>>> These patches are also available from
>>> 	https://github.com/ndyer/linux/commits/diagnostic-v4l
>>>
>>> Any feedback appreciated.  
>>
>> FYI: we're working on a new buffer type for meta data:
>>
>> https://patchwork.linuxtv.org/patch/33938/
>> https://patchwork.linuxtv.org/patch/33939/
> 
> One of the things I missed on your patchset is the content of the
> new format you added (V4L2_PIX_FMT_YS16). You should be patching
> the V4L2 docbook too, in order to add it there.

OK, will do. I also see that I forgot Kconfig changes for CONFIG_VIDEO_V4L2
etc.

> That's said, if the output is really an image, I don't think it
> should be mapped via the new V4L2_BUF_TYPE_META_CAPTURE. This type of
> buffer is meant to be used on non-image metadata, like image statistics
> to feed auto whitebalance and other similar AAA algorithms.

The output is raw touch data - i.e. a rectangular grid of nodes each having
an integer value. I think it is an image in some senses, although perhaps
it's a matter of opinion!

You can see an example of a Atmel MXT capacitive touch device here (using
this patchset):
https://www.youtube.com/watch?v=Uj4T6fUCySw

There are touch devices which can deliver much higher resolution/framerate.
For example here's the data coming from a SUR40 which is an optical touch
sensor but uses V4L in a similar way:
https://www.youtube.com/watch?v=e-JNqTY_3b0

> It could still make sense to use the new device type (VFL_TYPE_META) for
> such drivers, as we don't want applications to identify those devices as
> if they are a webcam.

I agree it may be a little confusing if things like Skype start picking up
these devices. Could we #define V4L2_INPUT_TYPE_TOUCH_SENSOR to solve that
problem?