Input: ALPS - handle 0-pressure 1F events

While a button is held SS5 hardware will give us single-finger packets
with x, y, and pressure equal to zero. This causes annoying jumps in
pointer position if a touch is released while the button is held. Handle
this by claiming zero contacts to ensure that no position events are
provided to the user.

Reviewed-by: Pali Rohár <pali.rohar@gmail.com>
Tested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Ben Gamari <ben@smart-cactus.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
index 8e15783d2932..a76e5c6fce54 100644
--- a/drivers/input/mouse/alps.c
+++ b/drivers/input/mouse/alps.c
@@ -1198,7 +1198,13 @@ static int alps_decode_ss4_v2(struct alps_fields *f,
                 f->mt[0].x = SS4_1F_X_V2(p);
                 f->mt[0].y = SS4_1F_Y_V2(p);
                 f->pressure = ((SS4_1F_Z_V2(p)) * 2) & 0x7f;
-                f->fingers = 1;
+                /*
+                 * When a button is held the device will give us events
+                 * with x, y, and pressure of 0. This causes annoying jumps
+                 * if a touch is released while the button is held.
+                 * Handle this by claiming zero contacts.
+                 */
+                f->fingers = f->pressure > 0 ? 1 : 0;
                 f->first_mp = 0;
                 f->is_mp = 0;
                 break;