Write combining for PowerPC processors?

[Benjamin Herrenschmidt]

> Would mprotect() also support enabling write combining on PPC systems? 
> Does X.org doe something similar to the MTRR stuff on PPC systems or is 
> it supposed to be entirely up to the kernel.

I told you that there is no CPU based write combining thing. Or rather,
the CPU itself doesn't care. It has to be dealt at the northbridge
level, and so is far from what mprotect() can do. PPCs have no MTRR
neither. So you'll have to look at your northbridge documentation and
see if you can do something like write combining.