diff options
authorDaniel Kurtz <djkurtz@chromium.org>2011-08-23 23:02:36 -0700
committerDmitry Torokhov <dmitry.torokhov@gmail.com>2011-08-23 23:08:20 -0700
commita93bd154d8571f1be84b04d7451ec72a490636d8 (patch)
parentInput: synaptics - decode AGM packet types (diff)
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 <djkurtz@chromium.org> Acked-by: Chase Douglas <chase.douglas@canonical.com> Acked-by: Henrik Rydberg <rydberg@euromail.se> Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
1 files changed, 14 insertions, 0 deletions
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