linux-kernel - [PATCH] input: mt: clarify the no-finger event

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Message-Id: <1269123486-2621-1-git-send-email-rydberg@euromail.se>
Date:	Sat, 20 Mar 2010 23:18:06 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Henrik Rydberg <rydberg@...omail.se>
Subject: [PATCH] input: mt: clarify the no-finger event

The current documentation does not explicitly specify how to report
zero fingers, leaving a potential problem in the driver implementations
and giving no parsing directive to userland. This patch defines two
equally valid ways.

Signed-off-by: Henrik Rydberg <rydberg@...omail.se>
---
 Documentation/input/multi-touch-protocol.txt |   16 ++++++++++++++++
 1 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/Documentation/input/multi-touch-protocol.txt b/Documentation/input/multi-touch-protocol.txt
index 8490480..eacb226 100644
--- a/Documentation/input/multi-touch-protocol.txt
+++ b/Documentation/input/multi-touch-protocol.txt
@@ -68,6 +68,22 @@ like:
    SYN_MT_REPORT
    SYN_REPORT
 
+Here is the sequence after lifting one of the fingers:
+
+   ABS_MT_POSITION_X
+   ABS_MT_POSITION_Y
+   SYN_MT_REPORT
+   SYN_REPORT
+
+And here is the sequence after lifting the remaining finger:
+
+   SYN_MT_REPORT
+   SYN_REPORT
+
+If the driver reports one of BTN_TOUCH or ABS_PRESSURE in addition to the
+ABS_MT events, the last SYN_MT_REPORT event may be omitted. Otherwise, the
+last SYN_REPORT will be dropped by the input core, resulting in no
+zero-finger event reaching userland.
 
 Event Semantics
 ---------------
-- 
1.6.3.3

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