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Date: Tue, 21 Feb 2017 09:29:53 +0100 From: "H. Nikolaus Schaller" <hns@...delico.com> To: Petr Cvek <petr.cvek@....cz>, Dmitry Torokhov <dmitry.torokhov@...il.com>, Pavel Machek <pavel@....cz>, Sebastian Reichel <sre@...nel.org>, Pali Rohár <pali.rohar@...il.com> Cc: 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>, 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 <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, linux-omap <linux-omap@...r.kernel.org>, Discussions about the Letux Kernel <letux-kernel@...nphoenux.org>, linux-iio@...r.kernel.org, kernel@...a-handheld.com, Aaro Koskinen <aaro.koskinen@...ia.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 Petr and all, > Am 20.02.2017 um 23:26 schrieb Petr Cvek <petr.cvek@....cz>: > > Hi > > Dne 20.2.2017 v 17:50 H. Nikolaus Schaller napsal(a): >> Hi Pavel, >> >>> Am 19.02.2017 um 23:19 schrieb Pavel Machek <pavel@....cz>: >>> >>> hi! >>> >>>>>> But as said I don't think we need float or fixed point for practical systems >>>>>> at all. >>>>> >>>>> So you are going to loose precision. And if userspace decides to >>>>> calibrate it slightly differently from kernel, lost precision will >>>>> matter. >>>> >>>> Really? >>> >>> Really. >>> >>>> Example: >>>> >>>> ADC values go 100 .. 3995 (i.e. touch margin is 100 steps in pre-calibration) >>>> >>>> This is scaled to let's say 0..640. >>> >>> Ok. Now userspace realizes that kernel alignemnt is off, and it would >>> want to scale it to 1..642. >> >> Screen coordinates are still 0..639. >> >>> That will mean that single pixel will be >>> inaccessible, right? >> >> Yes, that can happen if the additional user-space scale is > 1.0. >> >> As long as it is small (I expect <1.01 = 1% error in scale) it is >> barely noticeable. >> >> Therefore, I asked before: how big in pixels is your finger or stylus? >> Does this effect matter? >> >> A resistive touch is a man-machine-interface where people press buttons of at >> least 12x12 pixels size (or they are no longer visually recognizable). > > Smallest kernel font is 4x6 (i think) and I'm regularly using 8x8. I would like > to be able to select a single letter in the console. So you probably have exceptionally good eyes and reading a terminal on a touch screen is not a typical use case (except for us hard-core programmers). Anyways, if there is only a single pixel is not accessible due do rescaling and integer truncation effects (which is what Pavel complained) you can still select single letters in a 4x6 font. --- So, let's close commenting this patch here since in my opinion everything is said and the maintainers have decided not to accept it. I hope that I have not forgotten anyone to answer. Thank you very much to all participants for this discussion, because it was really enlightening to me and contains a lot of new perspectives. BR and thanks, Nikolaus
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