linux-kernel - Re: ALPS Trackpoint & pressure

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Date:   Tue, 6 Feb 2018 10:29:47 +1000
From:   Peter Hutterer <peter.hutterer@...-t.net>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Pali Rohár <pali.rohar@...il.com>,
        Masaki Ota <masaki.ota@...alps.com>,
        linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: ALPS Trackpoint & pressure

On Mon, Feb 05, 2018 at 02:49:55PM -0800, Dmitry Torokhov wrote:
> On Sun, Feb 04, 2018 at 04:08:39PM +0100, Pali Rohár wrote:
> > Hi! Now playing again with trackpoint connected to ALPS rushmore
> > touchpad and I'm seeking a nice feature. Via ALPS PS/2 protocol it
> > reports pressure of trackpoint. Parser for it is already implemented in
> > alps.c and value is assigned to variable "z". When I just move
> > trackpoint z is zero, when I push trackpoint while moving, then z is
> > number higher, maximally 32. Variable "z" is set, but unused.
> > 
> > Do we have some input interface which can be used to report this
> > pressure of trackpoint to userspace? I can use this feature e.g. as
> > additional button...
> 
> We could either do the conversion in kernel and emit BTN_LEFT, or
> report ABS_PRESSURE and see if userspace will be able to handle
> REL_X/REL_Y/ABS_PRESSURE device.
> 
> Adding Peter.

judging by trackpoint history, I'd leave the pressure->click conversion to
userspace because every trackpoint may need a different threshold setting.
"easier" to have this in userspace with dmi matches etc. plus, converting to
BTN_LEFT in the kernel means we cannot use it as a separate interaction
anymore.

That aside, I think exporting ABS_PRESSURE is fine, that's what it's there
for. Nothing will use it for now though, tbh not sure yet how that would be
exported from libinput. but worth filing a bug for, please assign it to me.

Cheers,
   Peter