Thomas Gleixner wrote:

Simply because you _ABUSE_ timer_init_hook() to set it up. Keep it self
contained and do not impose restrictions on the kernel core code, which
we have to maintain.
  

But time_init_hook is supposed to be abused.  That is its purpose - to 
be a hook for different time devices on SGI Visual Workstation and 
Voyager.  And we don't actually abuse it anymore, we just bypass it 
because the default timer init path wants to setup the PIT or the HPET, 
neither of which should be used in paravirt.

Zach