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

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Message-Id: <2FB9BB18-C84F-453B-8002-71A9CC8A253D@goldelico.com>
Date:   Tue, 21 Feb 2017 07:56:14 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Petr Cvek <petr.cvek@....cz>,
        Pali Rohár <pali.rohar@...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>,
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        Siebren Vroegindeweij <siebren.vroegindeweij@...mail.com>,
        Michel Verlaan <michel.verl@...il.com>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
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        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>, linux-iio@...r.kernel.org,
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        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 Dmitry,

> Am 20.02.2017 um 23:24 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
> 
> On Mon, Feb 20, 2017 at 2:21 PM, Petr Cvek <petr.cvek@....cz> wrote:
>> Hi,
>> 
>> Dne 20.2.2017 v 22:50 Dmitry Torokhov napsal(a):
>>> On Mon, Feb 20, 2017 at 1:27 PM, H. Nikolaus Schaller <hns@...delico.com> wrote:
>>>> 
>>>>> Am 20.02.2017 um 22:08 schrieb Pali Rohár <pali.rohar@...il.com>:
>>>>> 
>>>>> On Monday 20 February 2017 20:42:15 Pali Rohár wrote:
>>>>>> Hi Nikolaus!
>>>>>> 
>>>>>> On Monday 20 February 2017 17:50:04 H. Nikolaus Schaller wrote:
>>>>>>> Hi Dmitry,
>>>>>>> 
>>>>>>>> Input driver may set resolution for given axis in units per mm
>>>>>>>> (or units per radian for rotational axis ABS_RX, ABS_RY,
>>>>>>>> ABS_RZ), and if you check the binding, you can use
>>>>>>>> "touchscreen-x-mm" and "touchscreen-y-mm" to specify the size of
>>>>>>>> entire touch surface and set resolution from it so that
>>>>>>>> userspace can calculate the proper scaling factor.
>>>>>>> 
>>>>>>> How is this information exposed by the kernel to user-space? By
>>>>>>> scanning the DT file or tree?
>>>>>> 
>>>>>> Set input_abs_set_res() from kernel. And in userspace call EVIOCGABS
>>>>>> ioctl() on input device. Look at struct input_absinfo, you should
>>>>>> have all needed information here. This is generic input interface,
>>>>>> no DT is needed.
>>>>> 
>>>>> Looking at kernel code... via EVIOCSABS ioctl() you can even set
>>>>> resolution from userspace for specified input device.
>>>>> 
>>>>> So this could be potentially used for calibrating input device from
>>>>> userspace? (In case DT data will not fully match current HW)
>>>>> 
>>>>>> I hope that XServer is already using it for evdev devices...
>>>>>> 
>>>>>> For whole implementation look at evtest program. That should be good
>>>>>> starting point for your userspace implementation.
>>>>>> 
>>>>>> While I'm watching this discussion... in my opinion kernel should
>>>>>> just invert input axes (when needed)
>>>> 
>>>> It is questionable why it should do that at all then.
>>> 
>>> Because the task of the kernel is to provide unified view of the
>>> hardware. Axis swapping and inversion is needed to that "up" is always
>>> "up" and "right" is always "right".
>> 
>> Actually my Xorg calibration 3x3 matrix is fine with both axis inverted (on TSC2046).
> 
> Yes, you can make it work for your touchscreen as long as you know
> that it inverted somehow. How you gain this knowledge is the question.

I think by letting the user calibrate the touch (calib tools can detect
inversion and rotation by the tap gesture sequence). I got the impression
that this step is wanted anyways for getting maximum precision.

Or the user-space configuration for a specific device model knows that because
the developer has gained this knowledge once and predefined the rotation matrix
for e.g. X11 correctly. If he didn't e.g. for Replicant it is Replicant's bug...

So you do not need this knowledge passed to user-space at all. Hence my proposal
to get rid of touch inversion and flipping properties and code from the touch
screen drivers.

BR and thanks,
Nikolaus