Discard relative movement packets outside of [-127, 127] range to

prevent cursor jumps when using the trackpoint on some lenovo laptops.

Known affected models:
- Lenovo Thinkpad X13 Gen1
- Lenovo Thinkpad T14(s)
- Lenovo Thinkpad E15 Gen3
- Lenovo A475

With help from stsp@

OK stsp@ miod@ deraadt@ bru@

diff --git a/sys/dev/pckbc/pms.c b/sys/dev/pckbc/pms.c
index 0fc2910..4212134 100644 (file)
--- a/sys/dev/pckbc/pms.c
+++ b/sys/dev/pckbc/pms.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: pms.c,v 1.96 2022/04/06 18:59:30 naddy Exp $ */
+/* $OpenBSD: pms.c,v 1.97 2022/07/23 05:55:16 sdk Exp $ */
 /* $NetBSD: psm.c,v 1.11 2000/06/05 22:20:57 sommerfeld Exp $ */
 
 /*-
@@ -2610,6 +2610,16 @@ pms_proc_elantech_v4(struct pms_softc *sc)
 
        case ELANTECH_PKT_TRACKPOINT:
                if (sc->sc_dev_enable & PMS_DEV_SECONDARY) {
+                       /*
+                       * This firmware misreport coordinates for trackpoint
+                       * occasionally. Discard packets outside of [-127, 127] range
+                       * to prevent cursor jumps.
+                       */
+                       if (sc->packet[4] == 0x80 || sc->packet[5] == 0x80 ||
+                           sc->packet[1] >> 7 == sc->packet[4] >> 7 ||
+                           sc->packet[2] >> 7 == sc->packet[5] >> 7)
+                               return;
+
                        x = sc->packet[4] - 0x100 + (sc->packet[1] << 1);
                        y = sc->packet[5] - 0x100 + (sc->packet[2] << 1);
                        buttons = butmap[sc->packet[0] & 7];