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Input: mt - document devices reporting more touches than slots

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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>
This commit is contained in:
Daniel Kurtz 2011-08-23 23:02:36 -07:00 committed by Dmitry Torokhov
parent a6ca40c11e
commit a93bd154d8
1 changed files with 14 additions and 0 deletions
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14
Documentation/input/multi-touch-protocol.txt
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@ -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
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