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

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Date:   Tue, 21 Feb 2017 07:36:17 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     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>,
        Hans de Goede <hdegoede@...hat.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Petr Cvek <petr.cvek@....cz>,
        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" <linux-input@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Linux OMAP Mailing List <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>,
        Pavel Machek <pavel@....cz>,
        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,

> Am 20.02.2017 um 22:50 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
> 
> 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".

Hm. Why not touching pixel (0,0) on the touch is always pixel (0,0) on the
screen and touching pixel (639,479) is always (639,479)?

I think it is time to end this discussion.

It has show me how much a mess and half-baked area this is, which I did
not expect. I read contradicting messages from different people:

* don't break user space because it is carved in stone
* fix users space if you want to do it properly
* scaling by +/-1 and shifting by full range is ok
* scaling by ts-size/adc-range and shifting by adc_min is not ok
* full numeric ADC resolution is required but subpixel coordinates is not acceptable

I will monitor this to see if this becomes sorted out before submitting anything
new.

BR and thanks,
Nikolaus