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Input: docs: add more details on the use of BTN_TOOL

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The HID core stack used to be very relaxed considering the BTN_TOOL_*
usage. With the recent commits, we should now enforce to have only one
tool at a time, meaning that we can now express that requirement in the
docs.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
This commit is contained in:
Benjamin Tissoires 2022-02-03 15:32:26 +01:00 committed by Jiri Kosina
parent 5c20000a47
commit 42764f97e6
1 changed files with 5 additions and 1 deletions
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6
Documentation/input/event-codes.rst
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@ -137,7 +137,11 @@ A few EV_KEY codes have special meanings:
code should be set to a value of 1. When the tool is no longer interacting
with the input device, the BTN_TOOL_<name> code should be reset to 0. All
trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
code when events are generated.
code when events are generated. Likewise all trackpads, tablets, and
touchscreens should export only one BTN_TOOL_<name> at a time. To not break
existing userspace, it is recommended to not switch tool in one EV_SYN frame
but first emitting the old BTN_TOOL_<name> at 0, then emit one SYN_REPORT
and then set the new BTN_TOOL_<name> at 1.
* BTN_TOUCH: