Instruction OCM

[Stephen Neuendorffer]

Ah yes, I forgot about that little detail with the OCM.

It would be slick if these mappings were generated based on memory nodes
in the device tree for ARCH=powerpc.

Steve

> -----Original Message-----
> From: linuxppc-embedded-bounces+stephen=neuendorffer.name at ozlabs.org
[mailto:linuxppc-embedded-
> bounces+stephen=neuendorffer.name at ozlabs.org] On Behalf Of Temerkhanov
> Sent: Tuesday, May 20, 2008 4:11 AM
> To: mojtaba; linuxppc-embedded at ozlabs.org
> Subject: Re: Instruction OCM
> 
> On Tuesday 20 May 2008 13:19:26 mojtaba wrote:
> > Thank you for your email. But what is the solution to that? I have
seen
> > this in a thesis:
> >
> > "when using the OCM buses to connect memory, we can only use virtual
memory
> > as long as the virtual address is the same as the physical address,
which
> > is conceptually
> > the same as using a system without MMU. Therefore porting Linux to a
> > system based on an OCM memory system is not possible"
> >
> > http://ce.et.tudelft.nl/publicationfiles/1367_700_thesis.pdf
> >
> > Is that right? What do you suggest?
> >
> 
> 
> Getting OCM-based devices (and even memory) to work in Linux is
possible. All
> you need is to setup a mapping with virtual addresses equal to
physical (some
> info can be found here:
>
http://courses.ece.uiuc.edu/ece412/MP_Files/mp2/20060623-XUP-Linux-Tutor
ial-REVISION-FINAL.pdf)
> 
> Furthermore, if you really need to get the code running from OCM, I'd
suggest
> to setup such MMU mapping for OCM region very early - it can be done
in
> initial_mmu function at head_4xx.S. Look at line 936 (#if
> defined(CONFIG_SERIAL_TEXT_DEBUG) && defined(SERIAL_DEBUG_IO_BASE))
>  - that's very good point to start.
> 
> Regards, Sergey Temerkhanov
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