linux-kernel - Re: [PATCH v9 1/8] drivers:input:tsc2007: add new common binding names, pre-calibration, flipping and rotation

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Date:   Sun, 19 Feb 2017 18:04:14 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Pavel Machek <pavel@....cz>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Sebastian Reichel <sre@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Benoît Cousson <bcousson@...libre.com>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>,
        Michael Welling <mwelling@...e.org>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Javier Martinez Canillas <javier@....samsung.com>,
        Igor Grinberg <grinberg@...pulab.co.il>,
        "Andrew F. Davis" <afd@...com>, Mark Brown <broonie@...nel.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Alexander Stein <alexander.stein@...tec-electronic.com>,
        Eric Engestrom <eric@...estrom.ch>,
        Hans de Goede <hdegoede@...hat.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Petr Cvek <petr.cvek@....cz>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        Nick Dyer <nick@...anahar.org>,
        Siebren Vroegindeweij <siebren.vroegindeweij@...mail.com>,
        Michel Verlaan <michel.verl@...il.com>,
        linux-input@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        letux-kernel@...nphoenux.org, linux-iio@...r.kernel.org,
        kernel@...a-handheld.com, Aaro Koskinen <aaro.koskinen@...ia.com>,
        Pali Rohár <pali.rohar@...il.com>,
        Andrey Gelman <andrey.gelman@...pulab.co.il>,
        Haibo Chen <haibo.chen@...escale.com>
Subject: Re: [PATCH v9 1/8] drivers:input:tsc2007: add new common binding names, pre-calibration, flipping and rotation

HI Pavel,

> Am 19.02.2017 um 15:17 schrieb Pavel Machek <pavel@....cz>:
> 
> Hi!
> 
>> About loosing precision: there is already noise (jitter) in
>> real-world devices so that you can't achieve subpixel precision
>> anyways (unless your panel has a very low resolution). Please see my
>> answer to Dmitry some mails ago.
> 
> Maybe you can achieve better precision with averaging.

Can you? What do you want to average here? Multiple sequential measurements?
This makes the touch slower and hence imprecise and unuseable in another way.
Anyways, the tsc2007 chip can already do such averaging.

> 
> Anyway "input is already noisy" does not mean "so it is okay to
> degrade it more".

You have not yet said how you think it is degraded *more* than in your
example.

> Solve it properly. That means passing calibration
> data from kernel to userland.

As written before, the really proper solution would be to provide floating
or fixed point subpixel input events. Not arbitrarily scaling up in kernel
and leaving downscaling to user space (where everybody can make it worse).

But I don't think it is worth implementing subpixel touch events for real
world devices due to the jitter I mentioned.

BR,
Nikolaus


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