I wrote, and occasionally pretend to maintain, the HIL driver suite for Linux. The original version is in the 2.4 mainline, but never got merged into the 2.6 series. As there were a few problems with the original version (most noticeably a cosmetic bug that made the driver look like it was eating all available CPU cycles) I recently decided to adopt from USB the "HIDBP" idea of having a simpler driver for everyday use. So I recently wrote a 2.6-compatible version of the suite that does not include the more complicated driver (because that will take more time to port and I'd rather only do so once, after the new "driver-model" changes occur in the mainline.)
The new code is available here and this text file describing the driver is included inside the tarball. This will have to be evaluated before upload into the parisc-linux CVS and subsequent folding into the mainline, especially to fix m68k support which I undoubtably broke, and to decide on the proper positioning of the files in the linux tree (note that this driver replaces the old "hilkbd" driver which was not compatible with hp_sdc, so the new version will not be as complicated for the configuration system. As such, the tarball suggests moving hp_sdc and hp_sdc_rtc back to drivers/char rather than under drivers/input.)