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

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Date:	Thu, 24 Mar 2011 15:45:51 -0400
From:	Chase Douglas <chase.douglas@...onical.com>
To:	Chris Bagwell <chris@...bagwell.com>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Henrik Rydberg <rydberg@...omail.se>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	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 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.

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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