Re: [kvm-ppc-devel] [PATCH 2 of 3] [KVM] Add DCR access information

[David Gibson <dwg@au1.ibm.com>]

On Mon, Apr 07, 2008 at 10:25:32PM -0500, Hollis Blanchard wrote:
> On Monday 07 April 2008 20:11:28 David Gibson wrote:
> > On Mon, Apr 07, 2008 at 03:53:33PM -0500, Hollis Blanchard wrote:
> > > 1 file changed, 7 insertions(+)
> > > include/linux/kvm.h |    7 +++++++
> > >
> > >
> > > Device Control Registers are essentially another address space found on
> > > PowerPC 4xx processors, analogous to PIO on x86. DCRs are always 32 bits,
> > > and are identified by a 32-bit number.
> >
> > Well... 10-bit, actually.
> 
> The mtdcrux description in the ppc440x6 user manual says the following:
> 
> 	Let the contents of register RA denote a Device Control Register.
> 	The contents of GPR[RS] are placed into the designated Device Control 
> Register.
> 
> I take that to mean that we must worry about 32 bits worth of DCR numbers. 
> Perhaps I should say "no more than" rather than "always".

I think that's less misleading.  mtdcrux is very new, anything which
only has the mtdcr instruction certainly can't take DCR numbers above
10 bits, and I would expect that even on chips with mtdcrux the DCR
bus is probably still only 10-bits, although it could be extended.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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