The input (or devi-*) source base is organized as follows:
Figure 1. How the input SDK source base is organized.The lib directory contains "glue" code used by all drivers. It contains the command-line parsing code, the code used to manipulate modules and event bus lines, the code for resource manager interfaces, as well as the filter modules (rel, abs, and keyboard). In addition, the lib directory contains functions used by modules to request services of the input system (e.g., for attaching interrupts and pulse handlers, mapping device I/O space, etc.)
The hirun directory is an example of an actual input driver, devi-hirun. In this directory, you'll find various device and protocol modules.
The elo directory contains source for the "ELO" touchscreen drivers.
The sample directory contains sample code with lots of comments detailing the steps required to initialize your module, and what to put in your module's functions.
When writing your own input driver, you would create your own directory and put your new input modules there.