How the linux use BAT

[Noah yan]

I am studying source code for power mac. I am curious how linux use the BAT
MMU.
The address translation of BAT MMU is parallel with that of segment/page
MMU. BAT MMU is known as superpages in other architecture.
I am not good at the kernel coding part, hope that my questions share the
common fundermental with you and no stupid.

Here is my questions:
Is the kernel turn BAT MMU on? if so, a BAT array have been setup for that,
which part of the kernel code does this?
If BAT MMU is used, how about segment/page address translation in kernel, is
this also enabled and page table is setup?

If both BAT and seg/page are enabled, how the kernel make sure that the
correct one is used in adress translation?
  Is kernel really use the segment MMU of the powerpc, I have an impression
that most kernel only use the page MMU?


Thanks in advance.
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