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Re: [Xen-devel] [PATCH V2 3/4] xen/arm: Add support for Broadcom 7445D0 A15 platform.

On Fri, 2014-10-03 at 15:15 +0000, Jonathan Fraser wrote:
> On Fri, 2014-10-03 at 11:44 +0100, Julien Grall wrote:
> > Hello Jon,
> > 
> > On 02/10/2014 23:16, Jon Fraser wrote:
> > > This code supports the Broadcom 7445D0 32-bit A15 based platform.
> > 
> > While this patch has been acked and applied. Did you check that the (by 
> > default mapped 0xb0000000-0xb0020000) doesn't overlap to the RAM or 
> > another device on your platform?
> > 
> > Regards,
> > 
> I had a question about that.  This is a guest physical address, not the
> machine physical address?

It's guest physical but dom0 is mapped 1:1 so that is somewhat the same
as machine physical in this instance.

>   What are the restrictions?

It just needs to be a hole in the address space which isn't used for
anything else, so not RAM and not MMIO.

Since dom0 is 1:1 mapped for MMIO this means a hole in the machine
address map, or as a last resort an address used by something which
isn't given to dom0.

In 4.6 we are going to sort out a way of finding these addresses
automatically, so the suckitude of having to figure one out will go

> On our current platforms, memory always starts at 0 and we currently
> support between 1 and 6 GB.  There's always a 1GB hole at 0xc0000000.

I suppose this is an MMIO hole? Any free space in thatregion would do.

> However in the future, memory will start at 0x40000000 and extend
> contiguously past 32-bit space for up to 4GB of memory, then segmented
> in 36-bit address space.

In this case I guess the MMIO has moved to 0...0x40000000? Might need to
move the gnttab then too, or maybe we'll have fixed this in the core by
then (fingers crossed!)

> I haven't tried a guest with much more than 1GB of memory, but will
> try that today.
> Thanks,
> Jon

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