linux-kernel - RE: [PATCH] input: mt: introduce MT event slots

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Message-ID: <544AC56F16B56944AEC3BD4E3D5917712E567F0FEB@LIMKCMBX1.ad.analog.com>
Date:	Fri, 16 Apr 2010 08:40:37 +0100
From:	"Hennerich, Michael" <Michael.Hennerich@...log.com>
To:	Henrik Rydberg <rydberg@...omail.se>,
	Michael Poole <mdpoole@...ilus.org>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] input: mt: introduce MT event slots

Henrik Rydberg wrote on 2010-04-08:
> Michael Poole wrote:
> [...]
>>
>> For hardware with touch tracking support, what does a slot ID
>> provide for user-space that the tracking ID doesn't?  (TRACKING_ID
>> is already supposed to be unique for the life of the touch.)
>
> The purpose of the slot is twofold. Firstly, it reintroduces the
> ability for the kernel to filter ABS_MT events, which reduces the
> number of events emitted from the input core by a large factor.
> Secondly, it allows the driver to send partial information without
> breaking the protocol.
>
> The current MT protocol is designed for anonymous contacts, which
> dictates that all data for all fingers has to be sent between every
> synchronization point.
> Although this is fine for a handful of fingers, it does not play well
> with a larger scenario. The slot concept allows for a minimum of
> information to be emitted from the input core, without breaking
> compatibility with the current MT protocol. If a single attribute of a
> single finger of a single user is changed, the event sequence will
> simply be:
>
> SYN_MT_SLOT <slot-in-use>
> ABS_MT_ATTRIBUTE <some-value>
>
> If the contact gets destroyed and replaced by another one, there is
> not even a need to send that information explicitly, but this sequence
> would suffice:
>
> SYN_MT_SLOT <slot-in-use>
> ABS_MT_USER_ID <replacing-user>
> ABS_MT_TRACKING_ID <replacing-tracking-id>
> ABS_MT_ATTRIBUTE1 <some-value>
> ABS_MT_ATTRIBUTE2 <some-value>
> ...

Sorry, I must have missed something -
What is ABS_MT_USER_ID?

Regards,
Michael

Analog Devices GmbH      Wilhelm-Wagenfeld-Str. 6      80807 Muenchen
Sitz der Gesellschaft Muenchen, Registergericht Muenchen HRB 4036 Geschaeftsfuehrer Thomas Wessel, William A. Martin, Margaret Seif


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