linux-kernel - [PATCH 12/12] Input: docs: add more details on the use of BTN

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Date:   Wed, 26 Jan 2022 17:18:32 +0100
From:   Benjamin Tissoires <benjamin.tissoires@...hat.com>
To:     Jiri Kosina <jikos@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jonathan Corbet <corbet@....net>,
        Ahelenia Ziemiańska 
        <nabijaczleweli@...ijaczleweli.xyz>,
        Ping Cheng <pinglinux@...il.com>,
        Aaron Armstrong Skomra <skomra@...il.com>,
        Jason Gerecke <killertofu@...il.com>,
        Peter Hutterer <peter.hutterer@...-t.net>
Cc:     linux-input@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>
Subject: [PATCH 12/12] Input: docs: add more details on the use of BTN_TOOL

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@...hat.com>
---
 Documentation/input/event-codes.rst | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Documentation/input/event-codes.rst b/Documentation/input/event-codes.rst
index b24ae7d292cc..41b1fa647dab 100644
--- a/Documentation/input/event-codes.rst
+++ b/Documentation/input/event-codes.rst
@@ -137,7 +137,10 @@ 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. It is
+    however accepted to switch tool in one EV_SYN frame by setting the old
+    BTN_TOOL_<name> at a value of 0 and the new one at 1.
 
 * BTN_TOUCH:
 
-- 
2.33.1