linux-kernel - Re: [PATCH v3] Documentation: Add evdev type and code definitions

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Message-ID: <20110325003602.GA14035@barra.bne.redhat.com>
Date:	Fri, 25 Mar 2011 10:36:02 +1000
From:	Peter Hutterer <peter.hutterer@...-t.net>
To:	Chase Douglas <chase.douglas@...onical.com>
Cc:	Chris Bagwell <chris@...bagwell.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Henrik Rydberg <rydberg@...omail.se>,
	Nikolai Kondrashov <spbnick@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] Documentation: Add evdev type and code definitions

On Thu, Mar 24, 2011 at 03:45:51PM -0400, Chase Douglas wrote:
> On 03/24/2011 02:44 PM, Chris Bagwell wrote:
> > Looking good.  Minor comments at end.
> > 
> > On Thu, Mar 24, 2011 at 12:44 PM, Chase Douglas
> > <chase.douglas@...onical.com> wrote:
> >> +Touchscreens:
> >> +----------
> >> +ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
> >> +used to report when a touch is active on the screen.
> >> +BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported. BTN_TOOL_<name> events
> >> +should be reported where possible.
> > 
> > Does the real button event restriction solve something?  I know
> > majority of touchscreens are not sending a button today but usually
> > there is a button on the touchscreen frame that I'd image at least
> > some devices hooking it up to touchscreen interface.
> >
> > stylus+touchscreen combo devices are surely going to want to do this.
> 
> Perhaps this should be more clearly for touchscreen-only devices (not
> tablets or a mix). The problem we end up seeing is drivers who use
> BTN_LEFT because they want a touch to generate a primary button press in
> X. I want to prevent people from doing this.

suggest that they use BTN_0 instead then?

Cheers,
  Peter

> I believe mixed devices are hard to detect between tablets and
> stylus+touchscreen right now, as evidenced by the X evdev driver not
> handling the former by default while wacom is often used for the latter.
> However, with the device properties a userspace driver should be able to
> tell the two apart.
> 
> I'll rename this guideline: Touchscreens without stylus tools. Any issues?
> 
> >> +
> >> +Trackpads:
> >> +----------
> >> +Legacy trackpads that only provide relative position information must report
> >> +events like mice described above.
> >> +
> >> +Trackpads that provide absolute touch position must report ABS_{X,Y} for the
> >> +location of the touch. BTN_TOUCH should be used to report when a touch is active
> >> +on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
> >> +be used to report the number of touches active on the trackpad.
> > 
> > How about a Tablet?
> > 
> > Something like:
> > 
> > Tablets:
> > --------
> > 
> > BTN_TOOL_<name> events must be reported when a stylus or other tool is
> > active on tablet.  ABS_{X,Y} must be reported with the location of the
> > tool. BTN_TOUCH should be used to report when the tool is in contact
> > with the tablet. BTN_{STYLUS,STLUS2} should be used to report buttons
> > on tool itself and BTN_{LEFT,MIDDLE,RIGHT,1,2,etc} should be used to
> > report buttons on tablet.
> 
> Thanks for the addition! I'll add it in and add you on a SOB line if
> that's alright with you.
> 
> > Some tablets send ABS_PRESSURE with no BTN_TOUCH (why I said should
> > instead of must).  Probably this is not worth mentioning here?
> 
> Yeah, I'd leave that off as I think we want to set the guidelines to use
> BTN_TOUCH.
> 
> Thanks,
> 
> -- Chase
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