Bug 89949

Summary:	Fake finger switching bug in edge scrolling and tapping code
Product:	Wayland	Reporter:	Peter Hutterer <peter.hutterer>
Component:	libinput	Assignee:	Wayland bug list <wayland-bugs>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium	CC:	jwrdegoede, peter.hutterer
Version:	unspecified
Hardware:	Other
OS:	All
Whiteboard:
i915 platform:		i915 features:
Attachments:	evemu recording 0001-touchpad-delay-fake-finger-processing-until-the-EV_S.patch

Description Peter Hutterer 2015-04-08 05:19:03 UTC

Created attachment 114942 [details]
evemu recording

To switch from one to two fingers on a touchpad without slots, the event sequence is:
BTN_TOOL_FINGER 0
BTN_TOOL_DOUBLETAP 1
SYN_REPORT

On those touchpads, all touches are fake touches (sort-of). The above sequence will end the currently active touch and then re-start two new touches when the DOUBLETAP is seen. This triggers a bug message in the edge scrolling code - since there is no SYN_REPORT between the BTN_TOOL the touch is still in AREA state when it is re-triggered as a TOUCH_BEGIN.

This also affects the tapping code.

The sequence attached is enough to trigger it, full sequence in the bug here:
https://bugzilla.redhat.com/show_bug.cgi?id=1209151

Comment 1 Peter Hutterer 2015-04-08 07:05:53 UTC

Created attachment 114948 [details] [review]
0001-touchpad-delay-fake-finger-processing-until-the-EV_S.patch

actually, this looked easier than I thought at first. All we need to do is delay the fake touch start/end until SYN_REPORT time and that's only a few lines of shuffling around.

Comment 2 Hans de Goede 2015-04-08 08:30:10 UTC

Comment on attachment 114948 [details] [review]
0001-touchpad-delay-fake-finger-processing-until-the-EV_S.patch

Patch looks good and is:

Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Comment 3 Peter Hutterer 2015-04-08 22:58:32 UTC

commit ac0f5e799aec72ab392f6d79bbd97662000335e7
Author: Peter Hutterer <peter.hutterer@who-t.net>
Date:   Wed Apr 8 17:00:50 2015 +1000

    touchpad: delay fake finger processing until the EV_SYN

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