linux-kernel - Re: Touch processing on host CPU

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Message-ID: <54468E0D.2010200@itdev.co.uk>
Date:	Tue, 21 Oct 2014 17:47:09 +0100
From:	Nick Dyer <nick.dyer@...ev.co.uk>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jonathan Cameron <jic23@...nel.org>
CC:	Greg KH <greg@...ah.com>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Touch processing on host CPU

On 21/10/14 13:22, One Thousand Gnomes wrote:
>> If you will have touch processing in a binary blob, you'll also be going
>> to ages "Works with Ubuntu 12.04 on x86_32!" (and nothing else), or
>> "Android 5.1.2 on Tegra Blah (build 78912KT)" (and nothing else).
> 
> As well as not going upstream because there is no way anyone else can
> test changes to the code, or support it. Plus of course there are those
> awkward questions around derivative work boundaries that it is best the
> base kernel keeps well clear of.
> 
> If the data format is documented to the point someone can go write their
> own touch processor for the bitstream then that really deals with it
> anyway. Given the number of these things starting to pop up it would
> probably be good if someone did produce an open source processing engine
> for touch sensor streams as it shouldn't take long before its better than
> all the non-free ones 8).

Thank you for this input, I will feed it back.

> Given how latency sensitive touch is and the continual data stream I
> would be inclined to think that the basic processing might be better in
> kernel and then as an input device - providing it can be simple enough to
> want to put kernel side.

I would think that a touch processing algorithm (including aspects such as
noise and false touch suppression, etc) would be too complex to live
in-kernel. Getting decent performance on a particular device requires a lot
of tuning/customisation.

> Otherwise I'd say your bitstream is probably something like ADC data and
> belongs in IIO (which should also help people to have one processing
> agent for multiple designs of touch, SPI controllers etc)

This sounds promising. The only sticking point I can see is that a touch
frontend has many more channels (possibly thousands), which would seem to
impose a lot of overhead when put into the IIO framework. I will certainly
take a closer look at it.
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