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

HI Pavel,

Am 20.02.2017 um 20:29 schrieb Pavel Machek [off-list ref]:

Hi!

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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?

If I draw a line in gimp, I don't expect it to have steps because of
"barely noticeable" errors.

You can't draw a line with exactly 1 pixel distance on such a touch screen.

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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).

Resistive touch is used for drawing, too.

Yes, for taking handwritten notes but not for high-precision graphics design.
For that you take a bigger screen and zoom the relevant areas.

quoted

So the discussion boils down to "what gives the better usability?":
a) getting rid of the nasty user-space calibration step (and plethora of different tools)
b) getting highest theoretical precision which has a low practical relevance

I am in favor of a). Like most users we ask. A minority is in favor of b).
Since we don't exclude b) users from reconfiguring their system to get it done
as they like. I think this is the best we can achieve.

Do you even read what I wrote?

Because I presented way to have both a) _and_ b).

I am not aware that you did this. You made a proposal for the X system but not
for others, e.g. Replicant.

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No. You have to design interface such that they _can_ be improved, and
what you propose does not work that way.

It works. Please do real world tests...

You do a real world test on N900, and propose upgrade path.

I have no N900 running. But since it uses a tsc2004/5 controller which seems
to be quite similar, you can likely copy&paste some code or add the algorithm:

ABS_X = (touchscreen-size-x * (adc_x - adc_min_x)) / (adc_max_x - adc_min_x)

Thats it.

If you set touchscreen-size-x = (adc_max_x - adc_min_x) you get maximum precision
you can achieve with integer arithmetic. And if you set adc_min_x = 0 your
user-space gets what it would have got before adding such a formula and then you
can and must do calibration there.

Taking this as the defaults if none of the new properties is specified, makes
the scaling feature completely disappear. And I don't care about 2 additional
subtractions, one multiplication and one division per axis.

So the upgrade path is:
1. introduce new optional properties, parse and store them in the struct
2. set defaults for the optional properties as described above
3. add the formula to the code (1 line for each axis)
4. deploy - nobody will notice

Good so far.

Ok!

quoted

5. update the DT and remove user-space calibration - people will be happy
  that they do not have to calibrate first any more

You can't do this. And this is fatal problem with your proposal.

If I update the DT in the kernel, my users will be very unhappy,
because their screens will now be miscalibrated.

If you tell them that they should recalibrate once, after they upgrade
to Linux 4.12 because they no longer need it I doubt they will not be very
unhappy.

And as said I do not expect or force you to take step 5 for the N900 touch
screen. Not even step 1.

I would take this more sensitive if you would use the same chip.

New kernel must not
force users to update their userland at the same time.

Yes, it shouldn't. But to be honest, this is not my experience. I have to
tweak userland a little almost every time a new kernel merge window is done.
Admittedly not in the input system. And I may be using the wrong distribution.

But if you ever want to deploy better features it is really difficult to avoid.

Nevertheless, what problem do you have to implement steps 1-4 in kernel
and step 5 outside?

BR and thanks,
Nikolaus