linux-kernel - [PATCH 4.19 004/323] Input: elantench - fix misreporting trackpoint coordinates

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Message-Id: <20211124115718.974373122@linuxfoundation.org>
Date:   Wed, 24 Nov 2021 12:53:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Phoenix Huang <phoenix@....com.tw>,
        Yufei Du <yufeidu@...unc.edu>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>
Subject: [PATCH 4.19 004/323] Input: elantench - fix misreporting trackpoint coordinates

From: Phoenix Huang <phoenix@....com.tw>

commit be896bd3b72b44126c55768f14c22a8729b0992e upstream.

Some firmwares occasionally report bogus data from trackpoint, with X or Y
displacement being too large (outside of [-127, 127] range). Let's drop such
packets so that we do not generate jumps.

Signed-off-by: Phoenix Huang <phoenix@....com.tw>
Tested-by: Yufei Du <yufeidu@...unc.edu>
Link: https://lore.kernel.org/r/20210729010940.5752-1-phoenix@emc.com.tw
Cc: stable@...r.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/input/mouse/elantech.c |   13 +++++++++++++
 1 file changed, 13 insertions(+)

--- a/drivers/input/mouse/elantech.c
+++ b/drivers/input/mouse/elantech.c
@@ -433,6 +433,19 @@ static void elantech_report_trackpoint(s
 	case 0x16008020U:
 	case 0x26800010U:
 	case 0x36808000U:
+
+		/*
+		 * This firmware misreport coordinates for trackpoint
+		 * occasionally. Discard packets outside of [-127, 127] range
+		 * to prevent cursor jumps.
+		 */
+		if (packet[4] == 0x80 || packet[5] == 0x80 ||
+		    packet[1] >> 7 == packet[4] >> 7 ||
+		    packet[2] >> 7 == packet[5] >> 7) {
+			elantech_debug("discarding packet [%6ph]\n", packet);
+			break;
+
+		}
 		x = packet[4] - (int)((packet[1]^0x80) << 1);
 		y = (int)((packet[2]^0x80) << 1) - packet[5];