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    Subject[PATCH 5.15 004/917] Input: elantench - fix misreporting trackpoint coordinates
    Date
    From: Phoenix Huang <phoenix@emc.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@emc.com.tw>
    Tested-by: Yufei Du <yufeidu@cs.unc.edu>
    Link: https://lore.kernel.org/r/20210729010940.5752-1-phoenix@emc.com.tw
    Cc: stable@vger.kernel.org
    Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/input/mouse/elantech.c | 13 +++++++++++++
    1 file changed, 13 insertions(+)

    --- a/drivers/input/mouse/elantech.c
    +++ b/drivers/input/mouse/elantech.c
    @@ -517,6 +517,19 @@ 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];


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