Wacom

This article [[Article description::provides instructions for enabling touchscreen support for Wacom devices such as laptops, tablets, and ultrabooks, and the like.]]

Kernel
The following option is likely necessary for proper tablet functionality, even if the device is not an Intuos/Graphire tablet as it says in the description.

Recent touchscreen models may need other options like I2C_HID_ACPI:Some tablet models may also require these options:

Userspace driver
After kernel is configured, update the INPUT_DEVICES Portage variable using the wacom driver:

You should also create Xorg config file so that Xorg knows which driver should be used for the tablet. Example:

Xinput2 multitouch
The default setting of the  xinput driver has "gesture emulation".

When disabled, true multitouch events will be emitted instead and it can be used with Firefox multitouch.

Configuration
To list detected devices in the terminal, try. This command also allows tweaking things such as stylus buttons and draw space, but keep in mind that more work is necessary to make the changes persist after exiting an X session (see this discussion).