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Re: [Xen-devel] [RFC 15/19] xen/arm: Reserve region in guest memory for device passthrough

On Wed, 2014-06-18 at 19:33 +0100, Julien Grall wrote:
> On 18/06/14 19:14, Stefano Stabellini wrote:
> >> For non-PCI passthrough this size will unlikely happen. We always map a
> >> matter of few pages per-device.
> >>
> >> I think this size is enough for the time being. I plan to revisit it for
> >> PCI passthrough where we will be able to allocate some of them after 4G.
> >
> > Modern GPUs can easily exceed 512MB and they work on ARM.
> If it's like on x86, passthrough GPUs may also require firmware. At 
> least it looks like the case with some configuration on the Arndale, 
> which doesn't have any SMMU.
> I'd like to make this series as simple as possible so we can get 
> "quickly" a working solution to passthrough device with small amount of 
> MMIO region.
> So if you don't mind I suggest to bump the amount of MMIO region to 1GB, 
> I may need to shrink the first RAM bank, and think about bigger region 
> support in a follow-up series.

I think so long as we aren't painting ourselves into any ABI corners (I
don't think we are) then defering the handling of large devices is fine.

> Regards,

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