Instruction OCM

Stephen Neuendorffer stephen.neuendorffer at
Wed May 21 07:26:15 EST 2008

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.


> -----Original Message-----
> From: at
> at] On Behalf Of Temerkhanov
> Sent: Tuesday, May 20, 2008 4:11 AM
> To: mojtaba; linuxppc-embedded at
> 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
> > this in a thesis:
> >
> > "when using the OCM buses to connect memory, we can only use virtual
> > as long as the virtual address is the same as the physical address,
> > 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"
> >
> >
> >
> > 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:
> Furthermore, if you really need to get the code running from OCM, I'd
> to setup such MMU mapping for OCM region very early - it can be done
> initial_mmu function at head_4xx.S. Look at line 936 (#if
>  - that's very good point to start.
> Regards, Sergey Temerkhanov
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