Comment 3 for bug 1433444

Notes:
This touch screen reports itself as a Wacom USB device. This should be handled by the wacom_wac.c driver in the kernel. The 0x5010 Product ID is still not explicitly listed in wacom_wac.c as of the latest Linux kernel v4.0-rc4. However, it appears that a catch-all entry, USB_DEVICE_WACOM(HID_ANY_ID), was added to wacom_wac.c beginning in Linux kernel v3.18. This catch-all entry allows for basic touch support.

Solution Needed:
In order to get full support (e.g., multitouch), the wacom_wac.c needs to be updated with a description of the ThinkPad T550's Wacom device with Product ID 0x5010.

Semi-functional workaround:
Use a 3.18 or newer kernel.

I used a v4.0-rc4 mainline kernel (https://wiki.ubuntu.com/Kernel/MainlineBuilds; http://kernel.ubuntu.com/~kernel-ppa/mainline/v4.0-rc4-vivid/) to workaround the issue on my Thinkpad T550, but I believe a kernel as early as 3.18 would work. My T550's screen accepts basic touches at least. Each touch is treated the same way it would be if it was a mouse cursor left-clicking at that spot (or left-button dragging if I do a drag).

Workaround Note for Thinkpad T550 users:
When I first booted the v4.0-rc4 kernel, my Wi-Fi stopped working. The newer kernel was looking for a newer iwlwifi-7065D-*.ucode firmware binary than what was installed in /lib/firmware in 14.04. To resolve this, I downloaded https://wireless.wiki.kernel.org/_media/en/users/drivers/iwlwifi-7265-ucode-23.15.10.0.tgz, unpacked it, and copied the iwlwifi*.ucode files into /lib/firmware.