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

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Message-ID: <4BF7B438.8000001@euromail.se>
Date:	Sat, 22 May 2010 12:38:48 +0200
From:	Henrik Rydberg <rydberg@...omail.se>
To:	Rafi Rubin <rafi@...s.upenn.edu>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	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)

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.

> Seems to me like part of the problem here is still the overlap between tracking
> id and slot id.

Would you care to elaborate?

Cheers,
Henrik

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