linux-kernel - Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev3)

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Date:	Sat, 22 May 2010 13:16:38 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Henrik Rydberg <rydberg@...omail.se>
Cc:	Rafi Rubin <rafi@...s.upenn.edu>, Ping Cheng <pinglinux@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mika Kuoppala <mika.kuoppala@...ia.com>,
	Peter Hutterer <peter.hutterer@...-t.net>,
	Benjamin Tissoires <tissoire@...a.fr>,
	Stephane Chatty <chatty@...c.fr>,
	Michael Poole <mdpoole@...ilus.org>
Subject: Re: [PATCH 2/2] input: mt: Document the MT event slot protocol (rev3)

On Sat, May 22, 2010 at 12:38:48PM +0200, Henrik Rydberg wrote:
> Rafi Rubin wrote:
> > On 05/21/10 13:49, Henrik Rydberg wrote:
> >> Dmitry Torokhov wrote:
> >>> I guess this is where our disconnect lies as when I am looking at the
> >>> event names I view all *_MT_* events as related to the multitouch
> >>> protocol handling.
> >>>
> >> Yes. It is true that slot control is MT related, but I am looking at this from
> >> the perspective of future expansions like KEY_MT,  KEY_REL, and such, finding a
> >> way to signal to user space which events are handled via slots. If we had
> >> ABS_MT_SLOT, we would most likely get applications which store ABS_MT_SLOT as an
> >> attribute of the slot together with ABS_MT_POSITION_X, ABS_MT_TOUCH_MAJOR, etc,
> >> which is just not right. So the proposal is ABS_SLOT. May we have your verdict,
> >> please. :-)
> >>
> >> Henrik
> >>
> > 
> > How many fingers can type on cap of a key?
> 
> It depends on the size of the key, does it not. :-)
> 
> Getting serious, it is anyone's guess what will happen next, but I was picturing
> a table, with a large multitouch screen and buttons along the side of the table.
> Sure, we can do "ABS_BTN_0", "ABS_BTN_1", etc, but with slots in place, it seems
> more natural to use something like "ABS_MT_BTN_X". While at it, REL_MT event
> makes sense for those touchscreen techniques which register changes, like
> acoustic pulse recognition.
> 

While I could see relative MT events I do not understand the need for
slotted key events. We already allow pressing multiple keys at once and
if a device has 2 separate keys with the same event - they either should
be treated as one logical key or 2 separate input devices.

-- 
Dmitry
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