Re: Extended Addressing Mode

[Matt Sealey <matt@genesi-usa.com>]

Benjamin Herrenschmidt wrote:
> On Wed, 2008-10-22 at 08:08 -0500, Kumar Gala wrote:
>>> We are developing a board based on Freescale 8641D which can get
>> 4GB  
>>> of ram. So I need 4GB+IOs (~1GB) of physical addressing space.
>>> My plan is to put a part of this ram above of 4GB to keep accesses  
>>> to the IOs below the 4GB limit. It means non-contiguous ram  
>>> addressing and XAEN features to be working.
> 
> Why would you put the IOs below the 4G point ? It's actually easier
> to have the IOs up above, like a lot of 4xx do.

Because we're Genesi! And we have a firmware solution that 
kind of has to keep 32-bit pointers in the unlikely event that 
someone actually uses the client interface (besides yaboot!).

Having I/O in the 36-bit range could cause all sorts of 
explosions, and we're running real-mode so trapping and faking 
I/O accesses is REALLy difficult :}

-- 
Matt Sealey <matt@genesi-usa.com>
Genesi, Manager, Developer Relations