/proc/sys/dev

In this directory you will find subdirectories with virtual files that contain device specific parameters. The exact layout will depend on your hardware configuration and compiled in device drivers. So you might not have all subdirectories that are documented here.

Comments

HPET stands for High Precision Event Timer, and is a replacement for the RTC.

This directory contains one file: max-user-freq, which probably works the same way as /proc/sys/rtc/max-user-freq.

Documentation and example code can be found in the kernel sources: Documentation/hpet.txt

This directory contains one file: logging_level