1 files changed, 24 insertions, 6 deletions

diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
index 35a49bf57227..49e62201bb6b 100644
--- a/drivers/input/mouse/alps.c
+++ b/drivers/input/mouse/alps.c
@@ -938,18 +938,36 @@ static int alps_decode_packet_v7(struct alps_fields *f,
                 return 0;
         if (pkt_id == V7_PACKET_ID_UNKNOWN)
                 return -1;
+        /*
+         * NEW packets are send to indicate a discontinuity in the finger
+         * coordinate reporting. Specifically a finger may have moved from
+         * slot 0 to 1 or vice versa. INPUT_MT_TRACK takes care of this for
+         * us.
+         *
+         * NEW packets have 3 problems:
+         * 1) They do not contain middle / right button info (on non clickpads)
+         *    this can be worked around by preserving the old button state
+         * 2) They do not contain an accurate fingercount, and they are
+         *    typically send when the number of fingers changes. We cannot use
+         *    the old finger count as that may mismatch with the amount of
+         *    touch coordinates we've available in the NEW packet
+         * 3) Their x data for the second touch is inaccurate leading to
+         *    a possible jump of the x coordinate by 16 units when the first
+         *    non NEW packet comes in
+         * Since problems 2 & 3 cannot be worked around, just ignore them.
+         */
+        if (pkt_id == V7_PACKET_ID_NEW)
+                return 1;
 
         alps_get_finger_coordinate_v7(f->mt, p, pkt_id);
 
-        if (pkt_id == V7_PACKET_ID_TWO || pkt_id == V7_PACKET_ID_MULTI) {
-                f->left = (p[0] & 0x80) >> 7;
-                f->right = (p[0] & 0x20) >> 5;
-                f->middle = (p[0] & 0x10) >> 4;
-        }
+        f->left = (p[0] & 0x80) >> 7;
+        f->right = (p[0] & 0x20) >> 5;
+        f->middle = (p[0] & 0x10) >> 4;
 
         if (pkt_id == V7_PACKET_ID_TWO)
                 f->fingers = alps_get_mt_count(f->mt);
-        else if (pkt_id == V7_PACKET_ID_MULTI)
+        else /* pkt_id == V7_PACKET_ID_MULTI */
                 f->fingers = 3 + (p[5] & 0x03);
 
         return 0;