On Sat, Jul 16, 2022 at 08:26:49AM +0200, Stefan Hagen wrote:
> Hi,
>
> This is a workaround taken from Linux to mitigate sporadic cursor jumps
> due to a firmware bug. Known affected laptops are:
>
> - Lenovo Thinkpad X13 Gen1 (AMD version)
> - Lenovo Thinkpad T14s (AMD version)
> - Lenovo A475
>
> The trackpoint device is a touchpad/trackpoint combination that shows up
> in dmesg as "Elantech Clickpad, version 4".
>
> The faulty packets are reporting relative movements greater than 127 and
> cause the mouse cursor to jump into a corner of the screen. It only
> happens when the trackpoint is used. The touchpad is not affected.
>
> The bug report leading up to the fix:
> https://bugzilla.kernel.org/show_bug.cgi?id=209167
>
> The packet layout is described here:
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/drivers/input/mouse/elantech.c?h=v5.18.9#n492
>
> I'm running with this diff since r2k22 and haven't had a cursor jump or
> other negative side effects.
>
> Thanks to stsp@ for helping.
>
> Comments? OK?
ok stsp@, but I would remove the entire #ifdef DIAGNOSTIC printf block
before commit. Documenting the issue via the comment is good enough.
In general, printing messages in interrupt handlers is bad. And usually
done only under #ifdef DEBUG (code under DIAGNOSTIC is compiled in by
default). If a device ends up triggering this very often then a lot of
messages on the console could render the system unsuable.
> Index: sys/dev/pckbc/pms.c
> ===================================================================
> RCS file: /home/cvs/src/sys/dev/pckbc/pms.c,v
> retrieving revision 1.96
> diff -u -p -u -p -r1.96 pms.c
> --- sys/dev/pckbc/pms.c 6 Apr 2022 18:59:30 -0000 1.96
> +++ sys/dev/pckbc/pms.c 2 Jul 2022 20:23:45 -0000
> @@ -2610,6 +2610,22 @@ pms_proc_elantech_v4(struct pms_softc *s
>
> 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) {
> +#ifdef DIAGNOSTIC
> + printf("%s: discard faulty packet (elantech
> bug) "
> + "(state = %d,", DEVNAME(sc),
> sc->inputstate);
> + pms_print_packet(sc);
> + printf(")\n");
> +#endif
> + 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];
>
>
