[Linux-kernel-mentees] Advice on fixing the bug of MSFT0001:00 04F3:Touchpad being handled by hid_multitouch by mistake

Coiby Xu coiby.xu at gmail.com
Tue Aug 11 09:14:45 UTC 2020


I'm working on a touchpad device issue as reported on

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

         static const struct hid_device_id mt_devices[] = {
	        /* Generic MT device */

	        /* Generic Win 8 certified MT device */
	        {  .driver_data = MT_CLS_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?

Can anyone give an advice on which direction I should take? Thank you!

Best regards,

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