From a93bd154d8571f1be84b04d7451ec72a490636d8 Mon Sep 17 00:00:00 2001 From: Daniel Kurtz Date: Tue, 23 Aug 2011 23:02:36 -0700 Subject: [PATCH] Input: mt - document devices reporting more touches than slots Some devices are capable of identifying and/or tracking more contacts than they can report to the driver. Document how a driver should handle this, and what userspace should expect. Signed-off-by: Daniel Kurtz Acked-by: Chase Douglas Acked-by: Henrik Rydberg Signed-off-by: Dmitry Torokhov --- Documentation/input/multi-touch-protocol.txt | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/Documentation/input/multi-touch-protocol.txt b/Documentation/input/multi-touch-protocol.txt index 71536e78406f..543101c5bf26 100644 --- a/Documentation/input/multi-touch-protocol.txt +++ b/Documentation/input/multi-touch-protocol.txt @@ -65,6 +65,20 @@ the full state of each initiated contact has to reside in the receiving end. Upon receiving an MT event, one simply updates the appropriate attribute of the current slot. +Some devices identify and/or track more contacts than they can report to the +driver. A driver for such a device should associate one type B slot with each +contact that is reported by the hardware. Whenever the identity of the +contact associated with a slot changes, the driver should invalidate that +slot by changing its ABS_MT_TRACKING_ID. If the hardware signals that it is +tracking more contacts than it is currently reporting, the driver should use +a BTN_TOOL_*TAP event to inform userspace of the total number of contacts +being tracked by the hardware at that moment. The driver should do this by +explicitly sending the corresponding BTN_TOOL_*TAP event and setting +use_count to false when calling input_mt_report_pointer_emulation(). +The driver should only advertise as many slots as the hardware can report. +Userspace can detect that a driver can report more total contacts than slots +by noting that the largest supported BTN_TOOL_*TAP event is larger than the +total number of type B slots reported in the absinfo for the ABS_MT_SLOT axis. Protocol Example A ------------------ -- 2.20.1