Hi Paul,
I'm not following as to why you are patching the descriptor for the DFP,
my understanding is that this is fully supported at the moment (as
USB_DEVICE_ID_LOGITECH_DFP_WHEEL in the line after your patch).

Ah... you said 'Driving Force'.. not 'Driving Force Pro', but given the
confusing naming schemes I think I can be excused :-)
http://en.wikipedia.org/wiki/Gran_Turismo_official_steering_wheel#Model_comparison


However I do remember that there's a quirk with the logitech wheels that
they all pretend to be the same device, but some can be sent a magic
command which makes them disconnect and re-connect with a different USB ID
and with the larger steering range.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=blob;f=drivers/hid/hid-lg4ff.c;h=d7947c701f3063ac6c3683c29d3eca333b7ca1b0;hb=8b31849a113a8868eb2de692be5c9ecadae93ac9#l549


So in summary we need to be careful with "046d:c294 Logitech, Inc. Driving
Force"

Personally I have a Driving Force Pro, Driving Force Wireless and a G27
which all start with reporting this ID.

So a couple of questions:
1) Are you sure you have a "Driving Force"?
2) Does the ForceFeedback work for you?

Just for reference we moved the FF for the logitech wheels to hid-lg4ff
back in Aug 2011, I'm not sure which mainline kernel that was...

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=history;f=drivers/hid/hid-lg4ff.c;h=d7947c701f3063ac6c3683c29d3eca333b7ca1b0;hb=8b31849a113a8868eb2de692be5c9ecadae93ac9

Simon