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Date:   Sat, 18 Feb 2017 12:33:34 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        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, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        letux-kernel@...nphoenux.org, linux-iio@...r.kernel.org,
        kernel@...a-handheld.com, Aaro Koskinen <aaro.koskinen@...ia.com>,
        Pali Rohár <pali.rohar@...il.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 Sebastian,

> Am 18.02.2017 um 04:22 schrieb Sebastian Reichel <sre@...nel.org>:
> 
> Hi,
> 
> On Fri, Feb 17, 2017 at 12:40:41PM -0800, Dmitry Torokhov wrote:
>>> AFAIK there is no mainline board using the DT except ours (and the upcoming
>>> OMAP5-Pyra), so we shouldn't care too much. If you prefer, you can remove this
>>> compatibility property. We don't need it for our devices.
> 
> $ cd linux.git/arch
> $ git grep -l tsc2004
> arm/boot/dts/imx6qdl-nit6xlite.dtsi
> arm/boot/dts/imx7d-nitrogen7.dts
> arm/boot/dts/logicpd-torpedo-37xx-devkit.dts
> arm/boot/dts/omap4-var-som-om44.dtsi
> $ git grep -l tsc2005
> arm/boot/dts/omap3-n900.dts

Those are not relevant since tsc2004/5 and tsc2007 are independent drivers and don't
share code. Hence the N900 is not influenced by this patch series.

If it has a similar issue, it should be fixed of course.

> $ git grep -l tsc2007
> arm/boot/dts/imx28-tx28.dts
> arm/boot/dts/imx35-eukrea-cpuimx35.dtsi
> arm/boot/dts/imx51-eukrea-cpuimx51.dtsi
> arm/boot/dts/imx53-tx53-x03x.dts
> arm/boot/dts/imx6qdl-tx6.dtsi
> arm/boot/dts/imx6ul-tx6ul.dtsi
> arm/boot/dts/omap3-gta04.dtsi
> sh/boards/mach-ecovec24/setup.c

Sorry, I was a little imprecise here, because I looked for the min/max properties.
Of course, the imx devices use the tsc2007 as well.

Maybe we should edit all these DTS and set the "ti,report-resistance" property
by default. Then, no user should notice a difference.

Is any user/maintainer of these devices following this discussion and can comment?

> 
>> You seem to be treating DT data as something very fluid, which is wrong.
>> You need to treat it as a firmware, unlikely to change once device is
>> shipped. Unlike legacy platform data, the fact that DTS files are not
>> present in mainline does not mean that we can ignore such users and
>> change behavior at will.
>> 
>> That said, if driver behavior is out of line from the subsystem
>> expectations, we need to fix it.
>> 
>> 
>>> That the function name is wrong is a second issue and this double negation might
>>> confuse a litte.
>>> 
>>> Please test on a real device if the patched driver reports pressure now (unless
>>> ti,report-resistance is specified).
>> 
>> I unfortunately can not test this driver as I do not have the hardware.
>> So all my observations are from code and data sheets.
>> 
>> That said, what is the values emitted as ABS_PRESSURE when finger is not
>> touching the device, barely touching the device, or pressing firmly?
>> It seems that between TSC2007, TSC2004, TSC2005, and ADS7846, we have
>> confusion as to what is being reported.
> 
> As far as I can see all calculate Rtouch and ADS7846 reports
> (Rmax - Rtouch), which looks sensible.

I don't see where this subtraction from Rmax takes place for the tsc2007:

http://lxr.free-electrons.com/source/drivers/input/touchscreen/tsc2007.c#L131

> 
>> I am adding a few more folks to the CC so we can try and soft this out.
>> Sebastian, Pali, Pavel, any input here?
> 
> I think tsc200x works, since usually userspace is Xorg and I think
> it only cares for x/y coordinates + boolean pressure. Since
> no-pressure is correctly reported as 0, everything works as
> expected.

No pressure is usually treated as a special case in these drivers,
so reduction to "boolean" in user-space works well by accident and
might still hide a bug.

> I currently don't have X running on my N900 due some
> omapdrm bug, so I can't test this, sorry.

I usually look with evtest if ABS_PRESSURE is monotonic.

> 
> I suggest to put the resistance vs pressure thing in its own patch,
> that also fixes tsc200x-core and merge it to linux-next after the
> merge window.
> 
> -- Sebastian

BR and thanks,
Nikolaus



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