This prevents userspace applications from doing mmap() on /dev/hpet
even if there is no interrupt.
This seems to be the only part of the userspace interface that is
used in practice. Because of the availability of POSIX timers, it might
make sense to deprecate the HPET ioctl interface.
AFAIK it was intended to be similar to the RTC callback interface, but
that was before the generic high-precision timer stuff was introduced.
Regards,
Clemens
--