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

From: Petr Cvek <petr.cvek@tul.cz>
To: "H. Nikolaus Schaller" <hns@goldelico.com>, Pavel Machek <pavel@ucw.cz>
Cc: "Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
	"Sebastian Reichel" <sre@kernel.org>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Benoît Cousson" <bcousson@baylibre.com>,
	"Tony Lindgren" <tony@atomide.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Michael Welling" <mwelling@ieee.org>,
	"Mika Penttilä" <mika.penttila@nextfour.com>,
	"Javier Martinez Canillas" <javier@osg.samsung.com>,
	"Igor Grinberg" <grinberg@compulab.co.il>,
	"Andrew F. Davis" <afd@ti.com>, "Mark Brown" <broonie@kernel.org>,
	"Jonathan Cameron" <jic23@kernel.org>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Alexander Stein" <alexander.stein@systec-electronic.com>,
	"Eric Engestrom" <eric@engestrom.ch>,
	"Hans de Goede" <hdegoede@redhat.com>,
	"Benjamin Tissoires" <benjamin.tissoires@redhat.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Hans Verkuil" <hans.verkuil@cisco.com>,
	"Nick Dyer" <nick@shmanahar.org>,
	"Siebren Vroegindeweij" <siebren.vroegindeweij@hotmail.com>,
	"Michel Verlaan" <michel.verl@gmail.com>,
	linux-input@vger.kernel.org,
	devicetree <devicetree@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-omap <linux-omap@vger.kernel.org>,
	"Discussions about the Letux Kernel"
	<letux-kernel@openphoenux.org>,
	linux-iio@vger.kernel.org, kernel@pyra-handheld.com,
	"Aaro Koskinen" <aaro.koskinen@nokia.com>,
	"Pali Rohár" <pali.rohar@gmail.com>,
	"Andrey Gelman" <andrey.gelman@compulab.co.il>,
	"Haibo Chen" <haibo.chen@freescale.com>
Subject: Re: [PATCH v9 1/8] drivers:input:tsc2007: add new common binding names, pre-calibration, flipping and rotation
Date: Mon, 20 Feb 2017 23:26:59 +0100	[thread overview]
Message-ID: <e3dd020e-8590-6e65-9151-b5f1492debcb@tul.cz> (raw)
In-Reply-To: <6610D852-4717-47A7-BFDE-52C8E9E614BB@goldelico.com>

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@ucw.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.

cheers,
Petr