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@xxxxxxxxxx>
---
changes in v2:
- changed to explain that switching tool in one EV_SYN report
is not nice for userspace
---
Documentation/input/event-codes.rst | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/Documentation/input/event-codes.rst b/Documentation/input/event-codes.rst
index b24ae7d292cc..8741d390b184 100644
--- a/Documentation/input/event-codes.rst
+++ b/Documentation/input/event-codes.rst
@@ -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:
--
2.33.1
