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

Hi

Dne 20.2.2017 v 17:50 H. Nikolaus Schaller napsal(a):

Hi Pavel,

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Am 19.02.2017 um 23:19 schrieb Pavel Machek [off-list ref]:

hi!

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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.

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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.

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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