Re: Advice on fixing the bug of MSFT0001:00 04F3:Touchpad being handled by hid_multitouch by mistake

[Benjamin Tissoires <benjamin.tissoires@redhat.com>]

Hi,

On Tue, Aug 11, 2020 at 11:15 AM Coiby Xu <coiby.xu@gmail.com> wrote:
>
> Hi,
>
> I'm working on a touchpad device issue as reported on
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1887190.
>
> This touchpad device MSFT0001:00 04F3:Touchpad should be handled by
> hid_rmi. But currently hid-core.c chooses hid_multitouch by mistake,
>
>      1. When scanning this device's report descriptor, HID_DG_CONTACTID
>         usage is found. Thus group HID_GROUP_MULTITOUCH is assigned to
>         the device.
>      2. The flag HID_SCAN_FLAG_MT_WIN_8 is also found. Thus group
>         HID_GROUP_MULTITOUCH_WIN_8 is assigned to the device.
>      3. hid-multitouch.c claims handling devices with the group of
>         HID_GROUP_MULTITOUCH_WIN_8
>
>          static const struct hid_device_id mt_devices[] = {
>                 /* Generic MT device */
>                 { HID_DEVICE(HID_BUS_ANY, HID_GROUP_MULTITOUCH, HID_ANY_ID, HID_ANY_ID) },
>
>                 /* Generic Win 8 certified MT device */
>                 {  .driver_data = MT_CLS_WIN_8,
>                         HID_DEVICE(HID_BUS_ANY, HID_GROUP_MULTITOUCH_WIN_8,
>                                 HID_ANY_ID, HID_ANY_ID) },
>                 { }
>          };
>
> There are several potential solutions,
>      - Let the device vendor fix this problem since this device's report
>        descriptor shouldn't have the HID_DG_CONTACTID usage.
>      - Make it a special case by setting the device's group to
>        HID_GROUP_RMI in hid_scan_report when vendor id and product ID
>        are matched.
>      - hid-quirks.c seems to be designed to handle special cases, is it
>        suitable for this case?

AFAIU, the touchpad doesn't work at all with hid-multitouch. So I
guess the best is to add the VID/PID to hid-quirks.c in
hid_have_special_driver[], and add it to the hid-rmi driver too.
This way, you will ensure hid-rmi will pick up the device all the time.

Cheers,
Benjamin

>
> Can anyone give an advice on which direction I should take? Thank you!
>
> --
> Best regards,
> Coiby
>