/dev/input/by-path/<link> unreliable with MultiTouch device

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Hello All,

I am part of development of a product that uses touchscreens extensively. We have to maintain touchscreen calibration and X Display association across boots. We support up to six screens, 3 internal to our product, 3 external to our product. All internal screens have touchscreens with cables that don't move, so using the device /dev/ input/by-path/<devicelink> I could modify xorg.conf with an InputSection and associate the screen and touchscreen, include calibration, and every time the user returned, it was already calibrated and working correctly. It has worked great until we started adding multi-touch devices. The line of multi-touch devices we are using is manufactured my MosArt.

I added the defines for the products in my local kernel tree's driver/ hid/hid-ids.h and added the quirk for HID_QUIRK_MULTI_INPUT in hid- quirks.c. With the kernel 2.6.39.4 and earlier to 2.6.32.n, there is confusion with the /dev/input/by-path/<devlink>. These multi-touch devices show up with four entries in /dev/input/<dev>. From looking at the output of lsinput, two of the entries have identical information with regards to event bits. Only one of these identical entries in / dev/input/<dev> actually work; one reports 13 axis, one reports 3 axis. When the /dev/input/by-path/<devlink> points to the 'working' / dev/input/<dev> all is fine. This only happens 50% of the time and with three screens it is not likely to get all three right on any boot.

So, is this a good place to ask this question? What other information would be beneficial? I purposely left out a bunch of debug info so not to get too noisy.

Thanks in advance,
Donald Kayser
linux at kayser dot net
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