touchpad: detect and warn about kernel tracking pointer jumps

If a touch moves by more than 20mm within a single frame, reset the motion
history, effectively discarding the movement. This is a relatively common bug
and almost always needs a kernel fix, so add an explanatory page to the docs.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

diff --git a/doc/Makefile.am b/doc/Makefile.am
index 7a7c6cf17fb4aab5aa87723ddf9e11d93dc45a10..f56ed6a46337a2b64ff13622c6f10a4ef6beeb9a 100644 (file)
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -27,6 +27,7 @@ header_files = \
        $(srcdir)/tapping.dox \
        $(srcdir)/test-suite.dox \
        $(srcdir)/tools.dox \
+       $(srcdir)/touchpad-jumping-cursors.dox \
        $(srcdir)/touchpads.dox
 
 diagram_files = \

diff --git a/doc/page-hierarchy.dox b/doc/page-hierarchy.dox
index 1351a5eee847dd343b2976e5d9351dbeb37b0859..e47e98edcabf31d12562fa390d9a01b816ad7934 100644 (file)
--- a/doc/page-hierarchy.dox
+++ b/doc/page-hierarchy.dox
@@ -7,6 +7,7 @@
 - @subpage gestures
 - @subpage palm_detection
 - @subpage t440_support
+- @subpage touchpad_jumping_cursor
 
 @page touchscreens Touchscreens
 

diff --git a/doc/touchpad-jumping-cursors.dox b/doc/touchpad-jumping-cursors.dox
new file mode 100644 (file)
index 0000000..e581eb1
--- /dev/null
+++ b/doc/touchpad-jumping-cursors.dox
@@ -0,0 +1,54 @@
+/**
+@page touchpad_jumping_cursor Touchpad jumping cursor bugs
+
+A common bug encountered on touchpads is a cursor jump when alternating
+between fingers on a multi-touch-capable touchpad. For example, after moving
+the cursor a user may use a second finger in the software button area to
+physically click the touchpad. Upon setting the finger down, the cursor
+exhibits a jump towards the bottom left or right, depending on the finger
+position.
+
+When libinput detects a cursor jump it prints a bug warning to the log with
+the text <b>"Touch jump detected and discarded."</b> and a link to this page.
+
+In most cases, this is a bug in the kernel driver and to libinput it appears
+that the touch point moves from its previous position. The pointer jump can
+usually be seen in the evemu-record output for the device:
+
+<pre>
+ E: 249.206319 0000 0000 0000    # ------------ SYN_REPORT (0) ----------
+ E: 249.218008 0003 0035 3764    # EV_ABS / ABS_MT_POSITION_X    3764
+ E: 249.218008 0003 0036 2221    # EV_ABS / ABS_MT_POSITION_Y    2221
+ E: 249.218008 0003 003a 0065    # EV_ABS / ABS_MT_PRESSURE      65
+ E: 249.218008 0003 0000 3764    # EV_ABS / ABS_X                3764
+ E: 249.218008 0003 0001 2216    # EV_ABS / ABS_Y                2216
+ E: 249.218008 0003 0018 0065    # EV_ABS / ABS_PRESSURE         65
+ E: 249.218008 0000 0000 0000    # ------------ SYN_REPORT (0) ----------
+ E: 249.230881 0003 0035 3752    # EV_ABS / ABS_MT_POSITION_X    3752
+ E: 249.230881 0003 003a 0046    # EV_ABS / ABS_MT_PRESSURE      46
+ E: 249.230881 0003 0000 3758    # EV_ABS / ABS_X                3758
+ E: 249.230881 0003 0018 0046    # EV_ABS / ABS_PRESSURE         46
+ E: 249.230881 0000 0000 0000    # ------------ SYN_REPORT (0) ----------
+ E: 249.242648 0003 0035 1640    # EV_ABS / ABS_MT_POSITION_X    1640
+ E: 249.242648 0003 0036 4681    # EV_ABS / ABS_MT_POSITION_Y    4681
+ E: 249.242648 0003 003a 0025    # EV_ABS / ABS_MT_PRESSURE      25
+ E: 249.242648 0003 0000 1640    # EV_ABS / ABS_X                1640
+ E: 249.242648 0003 0001 4681    # EV_ABS / ABS_Y                4681
+ E: 249.242648 0003 0018 0025    # EV_ABS / ABS_PRESSURE         25
+ E: 249.242648 0000 0000 0000    # ------------ SYN_REPORT (0) ----------
+ E: 249.254568 0003 0035 1648    # EV_ABS / ABS_MT_POSITION_X    1648
+ E: 249.254568 0003 003a 0027    # EV_ABS / ABS_MT_PRESSURE      27
+ E: 249.254568 0003 0000 1644    # EV_ABS / ABS_X                1644
+ E: 249.254568 0003 0018 0027    # EV_ABS / ABS_PRESSURE         27
+</pre>
+
+In this recording, the pointer jumps from its position 3752/2216 to
+1640/4681 within a single frame. On this particular touchpad, this would
+represent a physical move of almost 50mm. libinput detects some of these
+jumps and discards the movement but otherwise continues as usual. However,
+the bug should be fixed at the kernel level.
+
+When you encounter the warning in the log, please generate an evemu
+recording of your touchpad and file a bug. See @ref reporting_bugs for more
+details.
+*/

diff --git a/src/evdev-mt-touchpad.c b/src/evdev-mt-touchpad.c
index 1974e2a06ae2ed0489fc0be3fb8a3c33d780bcda..4c8c3a3a1735ddb9b537bac68eb6c1cc6747871e 100644 (file)
--- a/src/evdev-mt-touchpad.c
+++ b/src/evdev-mt-touchpad.c
@@ -906,6 +906,25 @@ tp_need_motion_history_reset(struct tp_dispatch *tp)
        return rc;
 }
 
+static bool
+tp_detect_jumps(const struct tp_dispatch *tp, struct tp_touch *t)
+{
+       struct device_coords *last;
+       double dx, dy;
+       const int JUMP_THRESHOLD_MM = 20;
+
+       if (t->history.count == 0)
+               return false;
+
+       /* called before tp_motion_history_push, so offset 0 is the most
+        * recent coordinate */
+       last = tp_motion_history_offset(t, 0);
+       dx = fabs(t->point.x - last->x) / tp->device->abs.absinfo_x->resolution;
+       dy = fabs(t->point.y - last->y) / tp->device->abs.absinfo_y->resolution;
+
+       return hypot(dx, dy) > JUMP_THRESHOLD_MM;
+}
+
 static void
 tp_process_state(struct tp_dispatch *tp, uint64_t time)
 {
@@ -937,6 +956,14 @@ tp_process_state(struct tp_dispatch *tp, uint64_t time)
                if (t->pressure_delta < -7)
                        tp_motion_history_reset(t);
 
+               if (tp_detect_jumps(tp, t)) {
+                       log_bug_kernel(tp_libinput_context(tp),
+                                      "Touch jump detected and discarded.\n"
+                                      "See %stouchpad_jumping_cursor for details\n",
+                                      HTTP_DOC_LINK);
+                       tp_motion_history_reset(t);
+               }
+
                tp_thumb_detect(tp, t, time);
                tp_palm_detect(tp, t, time);
 

diff --git a/test/touchpad.c b/test/touchpad.c
index 6f483ee68f8ceba67e172c92b28a8e557f6e2d62..2dbb3463702f995d6f614514ed2e89561783eef2 100644 (file)
--- a/test/touchpad.c
+++ b/test/touchpad.c
@@ -4024,6 +4024,43 @@ START_TEST(touchpad_time_usec)
 }
 END_TEST
 
+START_TEST(touchpad_jump_finger_motion)
+{
+       struct litest_device *dev = litest_current_device();
+       struct libinput *li = dev->libinput;
+       struct libinput_event *event;
+       struct libinput_event_pointer *ptrev;
+
+       litest_touch_down(dev, 0, 20, 30);
+       litest_touch_move_to(dev, 0, 20, 30, 90, 30, 10, 0);
+       litest_drain_events(li);
+
+       litest_disable_log_handler(li);
+       litest_touch_move_to(dev, 0, 90, 30, 20, 80, 1, 0);
+       litest_assert_empty_queue(li);
+       litest_restore_log_handler(li);
+
+       litest_touch_move_to(dev, 0, 20, 80, 21, 81, 10, 0);
+       litest_touch_up(dev, 0);
+
+       /* expect lots of little events, no big jump */
+       libinput_dispatch(li);
+       event = libinput_get_event(li);
+       do {
+               double dx, dy;
+
+               ptrev = litest_is_motion_event(event);
+               dx = libinput_event_pointer_get_dx(ptrev);
+               dy = libinput_event_pointer_get_dy(ptrev);
+               ck_assert_int_lt(abs(dx), 20);
+               ck_assert_int_lt(abs(dy), 20);
+
+               libinput_event_destroy(event);
+               event = libinput_get_event(li);
+       } while (event != NULL);
+}
+END_TEST
+
 void
 litest_setup_tests(void)
 {
@@ -4144,4 +4181,6 @@ litest_setup_tests(void)
        litest_add_for_device("touchpad:bugs", touchpad_t450_motion_drops, LITEST_SYNAPTICS_TRACKPOINT_BUTTONS);
 
        litest_add("touchpad:time", touchpad_time_usec, LITEST_TOUCHPAD, LITEST_ANY);
+
+       litest_add_for_device("touchpad:jumps", touchpad_jump_finger_motion, LITEST_SYNAPTICS_CLICKPAD);
 }