Question on HPET timer reading from device driver?

[Samuel Xu]

HI:
I am a freshman for HPET timer. Previously, I use TSC counter, to use
rdtsc to get the time stamp. elapsed cycle can be counter from 2 time
stamps.
As a advanced replacement of TSC, I suppose HPET timer can be
conveniently to read time stamp from both kernel mode user  and user
mode apps.
While I failed to find a way to get time stamp value of HPET in Linux
kenerl (I am doing a driver and want to know elapsed cycle from driver
code).

I tried hpet_readl() from my driver code, while hit compiling error.
Is it a correct API for kernel driver to invoke?
I also read the Linux Documentation of HPET, which contain a user mode
demo app to generate a periodic timer via HPET, while missing the time
stamp reading.

Any hint?

Thanks!

Samuel
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