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Subject: Re: Unmapping pages from the linear addressing without HIGHMEM support
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Gerhard Pircher <gerhard_pircher@gmx.net>
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Date: Sun, 12 Mar 2006 11:07:41 +1100
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On Sat, 2006-03-11 at 14:28 +0100, Gerhard Pircher wrote:
> > --- Ursprüngliche Nachricht ---
> > Von: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > An: Gerhard Pircher <gerhard_pircher@gmx.net>
> > Kopie: linuxppc-dev@ozlabs.org, debian-powerpc@lists.debian.org
> > Betreff: Re: Unmapping pages from the linear addressing
> > without HIGHMEM support
> > Datum: Sat, 11 Mar 2006 10:13:30 +1100
> > 
> > > That would mean I cannot reuse the code in dma-mapping.c, right?
> > > Killing the BAT mappings or limiting the memory size covered by the
> > > BATs seems to be fairly easy, but I guess I have to setup my own page
> > > table for the reserved DMA memory area and implement my own
> > > alloc_pages() function!?
> > 
> > No, just limit the size of the BAT mapping and mark some of the top
> > pages of the address space reserved... That should be enough.
> > 
> Okay, I will try that first. Marking some of the pages as reserved sounds
> like the code you implemented for the uninorth_agp driver with this
> "agp_special_page". I guess I still have to modify the code in dma_mapping.c
> to use the reserved address space for the consistent memory allocation
> (CONSISTENT_BASE, CONSISTENT_END)?

Probably. I'm not sure about that code, I think those
CONSISTENT_BASE/END are only virtual addresses, the code still alocates
real pages below that from anywhere in memory, you may have to change
that, or maybe just 1:1 map that reserved area non-cacheable, and change
dma-mapping.c to not allocate any physical pages but just pick the one
matching the virtual ones it just allocated...;

Ben.