g_hid and hid-multitouch compatibility?

[Pablo Cases <pablo.cases@flatfrog.com>]

Hi all,

I have searched the net and the archives of linux-input for information on how to use the Linux g_hid kernel module on a device and the hid-multitouch kernel module on a host to communicate multitouch events. But unfortunately I can only get single touch working. 

Q: Has anyone successfully completed a g_hid <-> hid-multitouch setup? And is there a description somewhere of such setup?
Q: Is the Windows 7 multitouch USB HID descriptor the correct one to use also for Linux hid-multitouch? Or is some tweaking necessary?

DETAILED DESCRIPTION BELOW
The device is a Linux device that uses g_hid (currently 2.6.37 kernel) and a USB HID Report Descriptor for multitouch using two-touch parallel mode according to Microsoft document http://msdn.microsoft.com/en-us/windows/hardware/gg487437. 

On the host (ubuntu 11.04, 2.6.38 kernel) I register dynamically according to the description at http://lii-enac.fr/en/architecture/linux-input/multitouch-ubuntu-howto.html. Using the events/rdesc files in debugfs on Ubuntu 11.04 I have validated the parsing of the report descriptor and the input reports.

Example multitouch input report from /sys/kernel/debug/hid/0003:xxxx:yyyy.0002/events looks correct:
report (size 14) (numbered) =  05 03 00 a5 12 32 0e 03 01 99 14 32 0e 02 
Digitizers.TipSwitch = 1 
Digitizers.InRange = 1 
Digitizers.ContactID = 0 
GenericDesktop.X = 4773 
GenericDesktop.Y = 3634 
Digitizers.TipSwitch = 1 
Digitizers.InRange = 1 
Digitizers.ContactID = 1 
GenericDesktop.X = 5273 
GenericDesktop.Y = 3634 
Digitizers.ContactCount = 2

The first touch in the report is correctly presented both on Windows and on Ubuntu 11.04 (using ENAC's mtdiag tool with a minor tweak to display data from all devices not just multitouch ones). I can see in the debugfs files that the data for the second touch data is correctly transferred and interpreted (see above), but the mapping to the linux input system seems a bit strange though (see below). My guess is that I have not been correctly registered as a multitouch device. I'm assuming this also because I cannot see any activity from the hid-multitouch module other than it being initialized when I connect my device (probably another reason for the needed tweak in mtdiag above).

Example mapping from /sys/kernel/debug/hid/0003:xxxx:yyyy.0002/rdesc that does not look entirely correct for the second touch:
Digitizers.TipSwitch ---> Key.Touch
Digitizers.InRange ---> Key.ToolPen
Digitizers.ContactID ---> Absolute.Misc
GenericDesktop.X ---> Absolute.X
GenericDesktop.Y ---> Absolute.Y
Digitizers.TipSwitch ---> Key.Touch
Digitizers.InRange ---> Key.ToolRubber
Digitizers.ContactID ---> Absolute.?
GenericDesktop.X ---> Absolute.Z
GenericDesktop.Y ---> Absolute.Rx
Digitizers.ContactCount ---> Absolute.?
Button.0001 ---> Key.LeftBtn
Button.0002 ---> Key.RightBtn
Button.0003 ---> Key.MiddleBtn
GenericDesktop.X ---> Relative.X
GenericDesktop.Y ---> Relative.Y
GenericDesktop.Wheel ---> Relative.Wheel


Regards,
Pablo Cases

-------------------------
Pablo Cases, M.Sc.
Development Engineer Software
FlatFrog Laboratories AB
Magistratsvägen 10
22643 Lund
Sweden
Tel: +46 708 393816
Mail: pc@flatfrog.com
Web: www.flatfrog.com
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