The current debouncing code monitors events and switches on when events are
too close together. From then on, any event can be delayed.
Vicente Bergas provided an algorithm that avoids most of these delays:
on a button state change we now forward the change without delay but start a
timer. If the button changes state during that timer, the changes are
ignored. On timer expiry, events are sent to match the hardware state
with the client's view of the device. This is only done if needed.
Thus, a press-release sequence of: PRP sends a single press event, a sequence of
PRPR sends press and then the release at the end of the timeout. The timeout
is short enough that the delay should not be noticeable.
This new mode is called the 'bounce' mode. The old mode is now referred to as
'spurious' mode and only covers the case of a button held down that loses
contact. It works as before, monitoring a button for these spurious contact
losses and switching on. When on, button release events are delayed as before.
The whole button debouncing moves to a state machine which makes debugging a
lot easier. See the accompanying SVG for the diagram.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
The previous approach was to remember the last event and flush it at the right
time. The new approach is to update the device state during the frame and send
out the events at EV_SYN time.
This gives us two advantages: we are not dependent on the kernel order of how
events come in and we can process events depending on other events in the same
frame. This will come in handy later for button debouncing.
This is also the approach we have in the touchpad and tablet backends.
Two FIXMEs are left in place, the button debouncing code and the lid switch
code. Both need to be handled in future patches.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
